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The Clinical Approach to the Pruritic Dog
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Pruritus
The Clinical Approach to the Pruritic Dog
Susan I. Reinke, DVM*
In approaching any dermatologic problem, a clinician must follow a systematic procedure to obtain the information necessary in establishing a correct diagnosis. Due to the similarity in the appearance of many skin diseases, usually one cannot take a cursory glance and then proceed to an appropriate therapeutic regimen that will yield long-term satisfactory results. Unfortunately, the handling of a dermatologic case is very time consuming. It is necessary to obtain a thorough history and perform a complete physical examination with special emphasis on the skin. Often in evaluating a chronic case, about one half of the office visit will be spent obtaining a complete and accurate history. The remaining time is divided between a complete physical examination, appropriate diagnostic tests, making a diagnosis or list of differential diagnoses, explaining the findings to the client, prescribing medication, and giving directions to the client regarding the therapeutic regimen that he or she is to follow.
HISTORY
Obtaining a complete history can help rule in or rule out many different diseases. It is very useful to have the client fill out a questionnaire regarding the dermatologic history prior to the examination. 1 The client has a chance to remember pertinent details and hopefully provide concise answers to such questions as "What do you feed your pet?" which can be very time consuming if asked orally. The veterinarian can then quickly go over the questionnaire and rephrase certain important questions to see that the answers have been a correct interpretation of what was being asked. Many times a client's perception or reporting of the facts is inaccurate, and approaching a subject from several different angles will improve accuracy. The client may have responded that the animal itches, but further ques*Diplomate, American College of Veterinary Dermatology; Staff Dermatologist, Madera Pet Hospital, Corte Madera, California Veterinary Clinics of North America: Small Animal Practice- Vol. 18, No. 5, September 1988
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tioning may reveal that the animal is pruritic for only a few minutes when it awakes each morning, a fairly common occurrence (in the author's experience) in many "normal" dogs. The clinician must be careful not to ask misleading questions so that a false emphasis results. When atopy or food allergy dermatitis is suspected, it is common to ask the client if the face and feet are pruritic. The client's positive response may mislead the veterinarian if the questioning does not also include frequency, what other areas are pruritic, and how the amount of pruritus in other ;:treas compares to the degree of facial/pedal pruritus. A dermatology history form may be obtained from Allerderm, Inc. (P.O. Drawer 277, Hurst, Texas 76053).
SIGNALMENT Age The signalment may provide important information. Some diseases characteristically begin at a certain range of ages. Food allergy has been reported to occur most commonly between 4 months and 4 years of age, 2 but in the author's experience it can occur at any age. Atopy most commonly develops from 2 to 4 years of age but may be seen from 1 to 8 years. Flea allergy may begin any time after 4 months of age. Allergy developing after age 8 is considered uncommon unless an older animal is moved from one area of the country to another, thus exposing the dog to a new group of potential allergens. Scabies, Cheyletiella, or dermatophytosis may be present in the very young dog coming from an infested kennel. Localized demodicosis occurs most commonly in the 3- to 6-month-old puppy. Generalized demodicosis, including demodicosis limited to the feet, can occur at any age. Endoparasitic migration, although rare, occurs in young puppies.
Breed Certain diseases tend to have a breed predilection such as the increased incide nce of atopy in the terrier breeds, Dalmatian, Irish Setter, Miniature Schnauzer, Boston Terrier, and Lhasa Apso. Pruritic superficial pyodermas (short-haired dog pyoderma) and pruritic interdigital dermatoses tend to occur in shorthaired breeds such as Boxers, Dalmatians, Dachshunds, Great Danes, Doberman Pinschers , Weimaraners, English Bulldogs, and Mastiffs. Breeds with deep cutaneous folds such as the Chinese Shar Pei, Pekingese, English Bulldog, and Pug tend to develop irritations in their skin folds that often are pruritic. Nasal pyodermas occur in long-nosed breeds such as the Collie, Doberman Pinscher, German Shepherd, and setter/retriever breeds. Acute, moist, pyotraumatic dermatitis (hot spots) occurs commonly in the Golden Retriever and Saint Bernard as well as other breeds. However, one has to be careful not to assume a diagnosis just because of the dog's breed. The underlying problem of all pruritic, seborrheic West Highland White Terriers or Cocker Spaniels is not necessarily their genes. These animals deserve a complete dermatologic workup before they are assigned to that discouraging category of idiopathic
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seborrhea and before one merely attempts to control a disease with a probable genetic basis. Sex The sex of the dog may also point to certain diseases related to each sex's respective sex hormones. It should be noted if females are spayed, cycling normally if not spayed, or are prone to having false pregnancies. Pruritic seborrheic conditions that respond to ovariohysterectomy are seen in females associated with cystic ovaries or functional ovarian tumors. Sexual characteristics such as normal interest in females, mounting behavior, and lifting the leg to urinate should be noted in the intact male. Functional Sertoli cell tumor with its classic clinical signs may be pruritic if seborrhea is present. Severe, pruritic, seborrheic skin disease is described (in addition to other clinical signs) in the so-called male feminizing syndrome. 3
HISTORY
Basic Problem The client should be asked to briefly describe what he or she views as the current problem-itching, hair loss, red bumps, and so on. An animal may present with multiple problems, yet the client is concerned about one of them and is only interested in pursuing that problem. A dog may present with an acute otitis that is concerning the owner, and he or she may be totally unconcerned and disinterested in the dog's chronic flea allergy. Successful treatment requires client cooperation and especially so in dermatologic cases that often require frequent medicated baths, dips, flea powdering, medicating, and so forth in order to achieve any degree of success. Otherwise; the veterinarian's carefully written instruction sheet along with the prescribed medications and shampoos may be disregarded. Because of the many secondary problems that can occur, it is important to try to determine the nature of the initial problem. The client should be asked to describe what the lesions originally looked like and where they began. Was there hair loss, redness, pimples, itching? Primary lesions may be obscured .in the chronic, pruritic dermatologic case by excoriation, crusts, lichenification, and hyperpigmentation. When presented with a dermatologic case, one of the first things to determine is the presence of pruritus by asking if the dog scratches, chews, rubs, or licks. Using these specific words is necessary when referring to pruritus because using only one may elicit answers that give a wrong impression- that is, if asked if the patient scratches, the owner may respond with a dear "no" and yet fail to add that the dog does chew or lick. The presence or absence of pruritus immediately classifies the condition into one of two basic categories of skin disease-pruritic and nonpruritic. However, it must be remembered that there can be "cross-overs" such as hypothyroidism, a usually nonpruritic endocrine disease, which when present with a secondary pyoderma may be very pruritic. Where did the dog begin itching? Where is it itchy now? (Later,
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during the physical examination, the client can actually point out the pruritic areas.) Does the dog scatch and chew enough to justify the degree of alopecia or did the hair seem to just fall out? A dog with obvious flea allergy dermatitis with excessive alopecia and seborrhea might also have concurrent hypothyroidism. The degree of pruritus needs to be established. When and how often does the pet scratch, chew, or lick? A situation in which a dog sleeps in the bedrool)) with an owner who is a light sleeper may elicit exaggerated complaints of severe pruritus. It is useful to describe a setting of the owner and the dog spending a quiet evenirig while the owner reads or watches television, and then ask how often and. with what ihterisity does the pet chew, scratch, rub, or lick the skin in a period of an hour. Another useful technique to aid in determining the degree of pruritus is to leave the dog loose on the examination room floor while the history is being obtained from the owner. The veterinarian can casually observe if the dog is pruritic enough to continue scratching even in the stress cif an examination room. Onset When did the problem begin? How old was the dog when it began? Did it begin after the dog was boarded during summer vacation, after an improperly diluted flea dip was applied, after a dry carpet cleaner was used in the house, after a new kitten was obtained from the pound? Was the onset . gradual or sudden? Acute pyotraumatic dermatitis, insect bite hypersensitivities, autoimmune disease, skin fold dermatitis, and nasal pyoderma in long-nosed breeds tend to develop rapidly. In addition, the owner rhay describe other conditions as having a very rapid onset when, in fact, the disease was present for some time but suddenly seemed much worse and of concern to the owner. For example, the alopecia and pruritus from flea allergy dermatitis might not garner much attention until a hot spot develops, seemingly overnight. Other diseases have a slower onset, with the symptomatology gradually building to a crescendo. The first year that atopy or flea allergy is symptomatic, the signs may be minimal, but in subsequent years, the signs may become more intense with a quicker onset during the "allergy" season. Did the dog have the problem when the owner first obtained it? Contagious diseases such as those caused by external parasites (fleas, Sarcoptes, Cheyletiella, Otodectes) and dermatophytes (Microsporum, Trichophyton) may be present in a breeding situation or humane soCiety where an animal may have originated. Has the condition occurred previously with any seasonality or periodicity? Diseases such as atopy, thrombiculiasis (chiggers), and fleas tend to be seasonal. The irritation and subsequent licking of the feet during the winter months where streets are icy and/or salted is a seasonal condition in cold weather climates. Also, some dogs tend to develop irritation and licking during rainy, moist seasons of the year when the interdigital areas are constantly moist. This can be further complicated by feet with long, thick interdigital hair.
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Clinical Progression How has the condition progressed? An observant owner may be able to trace the classic progression of superficial pyoderma from an erythematous papule to pustule to crusted papule to epidermal collarette with central hyperpigmentation. Pyodermas often occur secondary to pruritus. An observant client may be able to state that the papules and pustules that are present currently were not present when the pruritus began. An important but difficult-to-answer question when dealing with allergic disease is: Which came first, the itch or the rash? In allergic diseases such as atopy, pruritus precedes the skin lesions, whereas pruritis may occur just as the papules and pustules are forming in pyoderma. The owner may report that the disease was initially seasonal but now isn't. Atopy often begins as a spring/summer disease of short duration (6 to 8 weeks). As the years progress, the period of pruritus gradually lengthens until it may be year round. However, the sudden lengthening of a formerly short pruritic season should be viewed with caution. A secondary pruritic pyoderma or the development of an unrelated condition such as scabies may cause a regularly occurring 6-week seasonal duration of pruritus in an atopic dog to suddenly lengthen dramatically. In handling the continued care of any chronic dermatologic case, the clinician should always be alert to details that may indicate that this is not just another recurrence of the previously diagnosed condition. Heredity The role of heredity may be important. A client who casually mentions that her pet now smells just like its mother did should alert the veterinarian to direct attention to the family medical history. Certain diseases such as idiopathic seborrhea in the Cocker Spaniel, German Shepherd, Brittany Spaniel, and West Highland White Terrier tend to have a familial tendency. Generalized demodicosis and atopy are both regarded as hereditary diseases. Contagion What other animals live in the same household or visit with any regularity? Asking how many pets a client owns may not provide the kind of information needed when a client shares a dwelling with other people who also own pets. In flea-endemic areas, multi-pet households cause flea allergy dermatitis to be included on the differential list if the lesions and distribution pattern are at all suggestive, whether or not fleas or flea excrement are present on the dog. Are any of the other household animals scratching or do they have skin problems? Contagious conditions involving ectoparasites (Sarcoptes, Cheyletiella, Otodectes, fleas) or dermatophytosis may be present on the other housemates. However, the lack of skin disease in these other animals does not rule out contagious disease. Sarcoptic mange may occur in only one dog in a multi-pet household (asymptomatic carrier phenomenon). 3 Recent exposure to other animals should be investigated. Was the dog groomed, boarded, at a pet show, picked up by the pound, in someone else's home, or was there a recent canine visitor at its home?
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Do any of the people living in the household have skin lesions and/or itching? Flea bites tend to occur on the lower legs of people. Canine scabies and Cheyletiella mites may cause lesions on the arms, trunk, and under tight areas of clothing such as under elastic bands. Dermatophytosis lesions tend to be located on exposed areas of skin. Environment What is the pet's environment? Is it inside only, inside/outside, or outside only? Is it allowed to roam free? Does it regularly go to another home to be "dog-sat"? These questions are particularly important when considering flea allergy and when instructing the owner about flea control. Where is the dog during the day? Where and on what does it sleep? Knowledge of the dog's physical environment is important when considering contact dermatitis. Are the symptoms worse when the dog is inside or outside? Dogs allergic to trees, grasses, and weeds may be noticeably worse when outside; conversely, dogs allergic to house dust, feathers , tobacco, or wool may be worse inside. Are the other household pets inside or inside/outside animals? The current patient might be an inside pet, but there may be others who are allowed to go outside and bring fleas or other contagious disease back inside. Do other pets come to visit? Skin Hygiene and Flea Control The general skin care should also be considered. What shampoos, rinses, or deodorizers are used on the dog? Some of the most extraordinary preparations have been used in canine hygiene. In his or her determination to clear up a skin condition, a client may have greatly increased the concentration of fleas dips or applied strong products that further irritate the skin. How often is the dog bathed? When was the last bath? A recent bath may have removed evidence of fleas as well as scales and crusts. Is the dog better or worse after bathing? Seborrheic animals, in particular, seem to have some relief from pruritus following bathing. However, some severely allergic dogs with very erythematous skin are more pruritic after a bath. Specific questions regarding fleas and flea control are very important in flea-endemic areas. When did the client last see fleas? What type of flea control is used-shampoo, powder, spray, dip, collar, systemic insecticides? Is it oral or topical? How often is it applied? Is the same flea control used and as vigorously on the other unaffected household animals? Is environmental control used? Inside and outside? How often? What methods and what brands? Taking time to get complete answers to these questions and then following up with proper flea control education is of utmost importance in handling the dermatologic patient. In the author's experience, failure to consider the effects that a few fleas can cause leads to one of the more common reasons for dermatologic referrals. Diet When discussing the animal's diet, clients will often volunteer their opinion that the pruritus could not be from the food because the diet has
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been switched several times between various commercial brands. Or they say that it couldn't be the food because the dog has been on the same diet for months. Both comments are in error. Most commercial diets contain the same basic ingredients, so switching from one to another will not cause any improvement in the patient with food allergy. Most food allergies occur after the pet has been on the food for a period of months to 2 years. Drug History Drug eruption has been documented in the dog and always has to be considered if the pet has been on any type of medication not only in recent days but also in the past weeks to months. 3 Food additives need also to be considered as a source of drug eruption. Previous Dermatologic Treatment What drugs are currently being used? What drugs have been used in the past for the skin condition? What was the response? These questions are important and can be very time consuming unless the owner has filled out a history sheet and hopefully brought treatment information from previous veterinarians. Even then, laboriously reading through copies of someone else's records can be slow and frustrating. A brief summary of the dermatologic history containing pertinent diagnostic testing results and treatments given by the previous veterinarian is much more useful. It is usually expeditious if the client brings the various medications, shampoos, dips, and so forth to the office. The client can then point to the various products and comment on the response to them. The clinician can also note whether the medication was finished or that only 5 tablets out of 30 were missing from the bottle that "didn't work." Lack of client compliance may account for lack of response when the previous diagnosis and prescribed treatment seem appropriate. Knowledge of the specifics regarding previous corticosteroid and antibiotic therapy is important. Previous correct use of the appropriate antibiotics used to empirically treat pyodermas (lincomycin, clindamycin, erythromycin, oxacillin, chloramphenicol, trimethoprim-sulfa combinations, clavulonated amoxicillin, or cephalosporins) may alert the clinician that this apparent pyoderma may contain resistant organisms or may be one of the other pustular skin diseases (demodicosis, dermatophytosis, pemphigus, subcorneal pustular dermatosis, and so on). At this point, it might be best to culture and/or biopsy rather than just do cytology of the pustule contents and empirically choose an appropriate antibiotic. Conversely, noting that inappropriate antibiotics (ampicillin, tetracycline, penicillin) have been used for an apparent pyoderma will direct the clinician toward selection of a more appropriate empirical antibiotic. Also, an appropriate antibiotic may have been chosen to treat an apparent pyoderma, but the previous veterinarian may have used an incorrect dosage or prescribed it for an inadequate length of time. In recurring pyodermas, the client may report that the drug did not work. On closer questioning, the truth may be that the lesions disappeared while the animal was taking the drug but recurred sometime after the antibiotic was withdrawn. Or the lesions may have disappeared, but the pruritus was still significant. Pursuing tests for
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underlying causes of pyoderma such as hypothyroidism and allergic disease as well as educating the client to the problem of pyoderma recurrence will yield better long-term results than just selecting another antibiotic. Dates of administration and dosages of corticosteroids in the last year should be obtained if possible. This knowledge is necessary for planning intradermal skin testing for inhaled allergies because long withdrawal periods may be necessary for the animal on continuous corticosteroid therapy. Also, recent corticosteroid use may have altered the lesions, resulting in an inaccurate picture of the true disease. The animal's response to previous corticosteroid therapy should be noted. Was the response complete or incomplete? How did the lesions and the amount and degree of scratching and so forth change during and after the therapy? Some conditions, such as atopy and contact dermatitis, may be completely responsive to minimal doses of corticosteroids (prednisone given at 1 mg per kg body weight). In other common conditions, such as flea allergy and pyoderma, the pruritus may be only decreased. In addition, the lesions of such diseases as pyoderma are usually still present even though slightly improved in appearance. Questions on previous therapy should also include what type of home therapy has been used on the pet and with what success. Tactful, nonjudgmental questions are always desirable, but they are apt to be especially rewarding here. It can be embarrassing for a client to admit some of the - home remedies that have been tried, especially if the dog's condition became worse after their use.
PHYSICAL EXAMINATION It is desirable to request that the client refrain from bathing the dog and stop all medications (except heartworm preventative, thyroid supplementation, and cardiac drugs) 2 weeks prior to the examination in order to present the condition in its most natural state. A routine physical examination should be performed and correlations determined, if they exist, between any abnormalities and the findings of the subsequent dermatologic examination. A thorough and systematic dermatologic examination, performed in adequate lighting, is mandatory. The general condition of the coat and skin should be noted. Is the hair shiny? Is the hair of normal thickness, texture, and length? Is the skin smooth and of normal thickness and elasticity, or is it greasy or excessively dry and scaly? Does the hair epilate easily? Easily epilated hair is associated with endocrine skin diseases but may also occur in localized areas as a result of excoriation and/or inflammation. A general distribution pattern of lesions should be noted. The client at this time can point out the pruritic areas and be questioned specifically as to the predominant areas of pruritus. Then a systematic examination can begin, usually starting with the head and proceeding distally, emphasizing the ears, ear margins, mucocutaneous junctions, mucosa, all aspects of the feet, nails and pads, genitalia, and lymph nodes. Going against the lay of the hair with the fingers may allow
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adequate visualization of the skin and hair, but shaving small areas may be necessary in heavily haired animals. It is essential for the clinician to become familiar with the different types of morphologic lesions and be able to recognize both primary and secondary lesions and what they represent. Primary lesions occur as the direct result of the disease process. Secondary lesions are a result of self~ trauma or of the progression of primary lesions. Failure to recognize that a papule might represent folliculitis and failure to identify epidermal collarettes are two common mistakes made by practitioners. Superficial pyodermas, which may be represented by papules, crusted papules, and epidermal collarettes and located on the ventral-lateral trunk, are very common in pn.iribc animals. The challenge then becomes to determine whether the pyoderma is secondary to a pruritic condition and only contributing to the pruritus or whether it is a primary condition that will respond fully to . antibiotic therapy. A progression of lesions may be present on the animal, which may help the clinician diagnostically. Papules often progress to pustules that rupture to leave an erosion. A crust forms, and eventually an epidermal collarette with subsequent central hyperpigmentation is evident. Lesions should be closely examined for their relationship to hair follicles. A papule with a hair emerging froin the center indicates a folliculitis for which the etiology will have to be determined. Distribution Pattern The distribution pattern is very important in ruling in or ruling out various pruritic diseases. Is it generalized or localized or occurring in specific regions such as the ventral abdomen? Symmetric or asymmetric? Symmetric lesions are not necessarily the classic indication of hormonal disease but can occur in allergic, ectoparasitic, and autoimmune diseases. 2 Many skin diseases have a characteristic distribution pattern of lesions and/or pruritus. Noting the pattern in conjunction with the history and types of lesions may lead to at least a list of differential diagnoses if not the diagnosis itself. Generalized Pruritus Many conditions may present with generalized pruritus or as generalized pruritus with emphasis in certain areas. The parasitic diseases [sarcoptic, demodectic, Cheyletiella mange; flea allergy dermatitis, thrombiculiasis (chiggers), pelode ra dermatitis, e ndoparasitic migration in puppies] may be generalized. However, the lesions and pruritus of sarcoptic mange tend to be concentrated on the ears and ear margins, elbows, and ventral thorax. Demodectic marlge usually begins on the head. The predominant areas of flea allergy dermatitis tend to be the lumbosacraVtail head/posteromedial aspects of the rear legs. Chiggers are usualiy found on the face, ears, and head but can also be found on the ventral body surfaces. Pelodera terids to cause pruritus in areas where the ground and skin come into contact. Pyodermas may be locaiized or generalized. Skin-fold pyodermas and the lesions of acute pyotraumatic dermatitis are usually localized. Superficial pruritic pyodermas may be generalized but most commonly occur along
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the ventral lateral trunk. Deep pyodermas have a similar distribution pattern that may also include the feet, legs, and face. Affected dogs tend to lick their feet, which may be a manifestation of pain and/or pruritus. Dogs with food allergy dermatitis may have generalized to regionally localized pruritus with erythema and papules, or the condition may mimic diseases such as flea allergy dermatitis, seborrhea, recurrent moist, pyotraumatic dermatitis, and otitis externa. 3 Dogs with atopy may present with generalized pruritus or with a facial/pedal/ventral distribution pattern. Contact dermatitis may be generalized if the irritant has been directly applied to the dog or localized if it is something in which the dog has been lying or walking. Autoimmune diseases may be pruritic and generalized, often having lesions on the head with some mucocutaneous orientation. Dogs with seborrhea often present with generalized pruritus. The lesions and pruritus tend to be more severe in fold and intertriginous areas, particularly neck folds, cranial tarsal areas, interdigital areas, and axillae. These animals often have a secondary superficial pyoderma. Treatment with appropriate antibiotics arid frequent shampooing will often alleviate much of the discomfort, odor, and lesions of a chronic seborrhea of unknown etiology. Several endocrine-related dermatoses may be associated with generalized, or at least regional, pruritus. The pruritus in these traditionally nonpruritic diseases is usually due to seborrheic changes or secondary pyoderma. Hypothyroidism may present with seborrhea and/or pyoderma, - both of which may be pruritic. So-called type I ovarian imbalance in unspayed females may have generalized seborrhea arid/or seborrhea with licheq.ificatibn and hyperpigmentation of the perivulvar area. 3 Functional Sertoli cell tumors may be pruritic if sufficient seborrhea is present. Socalled male feminizing syndrome (which may actually be due to a nondiagnosed Sertoli cell tumor) presents with seborrhea and pruritus. 3 Calcinosis cutis (calcium deposits in the skin) that can occur with hyperadrenocorticism (Cushing's disease) tends to occur on the trunk and can be very pruritic, particularly when secondarily infected. Mycosis fungoides, a T-cell lymphocytic neoplasia of the skin, may begin as a generalized, erythematous, scaling pruritic condition. It progresses to plaque and nodular stages. Mastocytomas, especially when diffuse, may produce marked pruritus. 4 Other cutaneous neoplasms or cysts are not generally regarded as pruritic, although at times a dog may scratch or chew at them. Facial Pruritus Demodectic mange (sometimes pruritic), sarcoptic rriange, atopy, and food allergy usually present with facial lesions and/or pruritus. Contact dermatitis, especially of the muzzle region, can occur through rooting or contact with certain vinyl food dishes (rarely seen in recent years). The autoimmune diseases (pemphigus, pemphigoid, lupus erythematosus) often begin ori the head and rriay be pruritic. Breeds with prominent facial folds may have pruritic irritations in those areas either as a continual problem or sporadically. Diseases of the eyelid margins may lead to pruritus related to the orbital and periorbital area.
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Long-nosed breeds may present with a relatively acute onset of lesions on the bridge of the nose including erythema, scaling, papules to crusted papules, alopecia, excoriation, erosion, and ulceration. The differential diagnoses to consider are demodicosis, dermatophytosis, nasal pyoderma; autoimmune disease (pemphigus and lupus erythematosus), and acute insect bite hypersensitivity. Nasal solar dermatitis was previously considered a differential diagnosis, but recently most biopsies of these cases have been diagnosed histologically as lupus erythematosus. Foreign bodies of the mouth, nose, eye, and ear should also be considered in any acute onset of facial rubbing, scratching, or pawing. Pinnal Pruritus Pruritus of the pinnae may occur in atopy and food allergy, contact allergy from an otic preparation, chiggers, and fly strike. Sarcoptic mange classically involves the pinnae, especially the margins, but similar scaling and crusting of the pinnal margin can occur in certain dogs with seborrhea, particularly spaniel-type breeds. Leishmaniasis, not normally a pruritic disease, may present with slightly pruritic, excoriated, nodular lesions on the pinnae (as well as the typical scaling lesions of the ears, face , pressure points, and/or entire body.) Diseases of the external ear canal, of course, may cause localized scratching and rubbing with resultant excoriation and alopecia of the pinnae. Pedal Pruritus When a dog is presented with pruritus and/or lesions related to the feet, a skin scraping is mandatory to rule out demodectic mange. Other conditions to consider in the differential diagnosis of pedal pruritus are atopy, food allergy dermatitis, allergic or irritant contact dermatitis, interdigital pyoderma, sterile interdigital pyogranuloma, autoimmune disease, Pelodera dermatitis, foreign bodies, and other digital and interdigital inflammatory diseases. Some dogs, especially Poodles and Miniature Schnauzers, tend to display neurotic licking of one or more feet. FaCial/Pedal Pruritus Facial/pedal (with often axillary or generalized) pruritus is commonly associated with atopy and food allergy. The dog may rub its muzzle and/or scratch at the face and ears. Caution must be exercised in interpreting client's reports of facial rubbing. Frequency is important. It is the author's observation that some dogs normally rub their faces after eating. The allergic animal will usually have signs of excoriation and alopecia involving the periocular, pe rioral, and pinnal areas. Lumbosacral and Tailhead Pruritus In appropriate climates, lumbosacral and tailhead pruritus, alopecia, and excoriation are classically interpreted as flea allergy dermatitis. However, this distribution pattern has also been seen in atopy and food allergy dermatitis. 5
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Axillary and Inguinal Pruritus Pruritic diseases commonly involving the axillary/inguinal regions are flea allergy dermatitis, sarcoptic mange, pyoderma (superficial and deep), atopy, food allergy, and contact dermatitis. Most of these diseases, of course, present with pruritus and lesions elsewhere on the body. DIFFERENTIAL DIAGNOSES After the history and physical examination are completed, a list of differential diagnoses should be made. By careful consideration of the information now at hand, the clinician can hopefully limit this list to a reasonable, workable number. Unfortunately, it is often not possible to make an absolute diagnosis without having to resort to differential diagnoses and diagnostic testing to rule in or rule out each diagnosis. In order to gain the client's confidence and cooperation, the clinician must now explain why this is the appropriate approach to making a dermatologic diagnosis. It is helpful to say that the skin can only respond in a certain number of ways (it can become erythematous, scaly, papular/pustular, and so on), and many different diseases can cause each of those signs. Therefore, a certain number of tests are required to (hopefully) reach a diagnosis through the systematic process of eliminating the various differential diagnoses. Depending on the ease of future visits (due to distance travelled or job requirements), financial limitations, severity and chronicity of the condition, client motivation and frustration, the tests may be completed at the first visit; more likely, a tiine table will be set up, and tests for the more likely diseases will be scheduled first. If the results are negative, further testing can then be scheduled. Unfortunately, in the general practice situation, many clients are unwilling to pursue a diagnosis involving many tests. Many tiines, the general practitioner is faced with "Oh, just give him a cortisone shot, Doc." When the veterinarian is faced with lack of interest for diagnostic testing, the client will often accept trial therapy, which will be discussed later. Trial therapy is important in the elimination of several important differential diagnoses of pruritic canine skin disease. DIAGNOSTIC TESTING Skin Scraping and Fungal Culture In the majority of cases, the mm1mum database includes properly performed skin scrapings and fungal culture. Wood's light examination is fraught with so many false-positives that it should not be done unless a fungal culture is done concurrently. Even in the hands of experienced mycologists, potassium hydroxide preparations of hair shafts are considered very difficult to evaluate for evidence of dermatophytes. Cytology and Bacterial Culture and Sensitivity
If a vesicle or pustule is present, cytologic examination of the contents smeared on a glass slide and stained with an appropriate stain such as Diff
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Quik should be made. Rod or coccoid bacteria can be visualized as well as types of white blood cells. Bacteria located within white blood cells is an indication that the bacteria seen are part of a disease process and are not just bystanders. Also it is an indication that at least one part of the immune system (phagocytosis) is functioning. Significant numbers of acantholytic cells (large, rounded, dark-staining epithelial cells) are indicative of pemphigus. Cytology is a more appropriate test than bacterial culture and sensitivity in the initial presentation of a pustular disease. Because the vast majority of canine pyodermas are caused by coagulase-positive Staphylococcus species, the presence of cocci in the smear will direct the clinician towards choosing one of the several known effective drugs against Staphylococcus species. If a mixed bacterial population is seen or if the pustular disease is recurrent or nonresponsive to antibiotics or is a deep pyoderma, a bacterial culture and sensitivity are indicated. Blood Screens A chemical profile and/or complete blood count may be indicated if systemic illness or endocrine disease is suspected. A minimum level of 1,000 lymphocytes per ml is considered necessary for basic immune competence. These blood tests are often overused in the dermatologic patient. The client's money is often better spent on other tests or trial therapies. Thyroid and adrenal evaluation may be performed at the initial visit if the clinical signs are indicative. The antinuclear antibody test may be performed when autoimmune disease is suspected. Biopsy Biopsy for routine histologic examination is usually not one of the initial tests performed unless the lesions appear to be something that the clinician has never seen before, a diagnosed condition not responding to appropriate therapy, a suspected neoplasia, or a suspected autoimmune disease. Although they do not always provide a diagnosis, the results can often rule out some of the proposed differential diagnoses. Taking multiple sections of primary lesions is preferred. If autoimmune disease is suspected, a section should be saved in Michele's medium for immunofluorescent testing. Biopsying appropriate lesions and providing adequate history and physical examination findings to the histopathologist will result in much more useful information. Also, care should be taken in selecting a histopathologist. A veterinary dermatopathologist, a dermatologist with special training in dermatopathology, or a general veterinary pathologist with special interest in the skin is preferred. A discussion of biopsy techniques as well as pertinent information on other diagnostic tests is available in various veterinary texts. 2· 3 Skin Testing Intradermal skin testing for atopy is best performed by a specialist or other clinician seeing enough dermatologic cases to enable frequent testing. Intradermal skin testing has an element of art as well as science that is best developed with frequent practice. As a general practice, this test is often
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performed after other differential diagnoses have been ruled out unless the history and clinical signs are classic for this condition.
TRIAL THERAPY Response to therapy can be an important method of ruling in or ruling out various differential diagnoses. It is also one type of "test" that usually has good client acceptance. However, the client must be educated as to what changes he or she is to observe from the trial therapy, such as healing of lesions and cessation of pruritus. The client must also be aware of what to watch for once the trial therapy is discontinued. Paracitacidals Response to paracitacidals is almost always included as a diagnostic consideration in flea-endemic climates. A full explanation of the steps necessary to control fleas on all the household animals as well as the pet's environment is essential in ruling out fleas as a source of pruritus. Client cooperation can be best obtained by explaining that all possible sources of pruritus must be eliminated, the most obvious of which is often fleas. Often the client is anxious to go on to more "glamorous" etiologies of pruritus. It must be explained, for example, that it is impossible to know if the dog is responding to a food elimination diet that is manifested by decreased pruritus if fleas, which are known to cause pruritus, are still on the dog. A client will often agree to a set period of time such as 3 to 4 weeks for doing maximum flea control as a "flea allergy test." Because sarcoptic mange is difficult to diagnose via skin scraping, it is often diagnosed in retrospect after a positive response to appropriate paracitacidals (lime sulfur, amitraz, ivermectin, certain organophosphates). Antibiotics Pyoderma is one of the most underdiagnosed conditions in veterinary dermatology. When presented with a papular or crusted papular condition, a trial period of an appropriate empirically chosen antibiotic may be indicated. Having the client closely observe the pet during and after the antibiotic treatment may help determine not only if the lesions are antibiotic responsive and thus probably a pyoderma but also whether the pyoderma is a pruritic pyoderma or a pyoderma that has occurred secondary to pruritus from another condition. In the first instance, the pruritus will disappear as the lesions heal. In the second, the pruritus will persist even after the lesions are healed. It could be argued that biopsy is a more reliable method of diagnosing pyoderma. Perhaps that is true, but the use of antibiotics answers two questions: Are the lesions antibiotic responsive and is the pruritus antibiotic responsive? In addition, a trial period of antibiotic treatment is generally less expensive than biopsying. Also, it is sometimes difficult to locate an appropriate lesion that will result in a clear-cut diagnosis.
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Food Elimination Diet The only accepted method for diagnosing food allergy dermatitis is with a specific food elimination diet. A 3-week diet consisting of lamb and brown rice or potatoes is commonly used. The client must be instructed to observe the level of pruritus while the animal is on the diet as well as when the diet is terminated. Care must be taken to be sure that other concurrent sources of pruritus (fleas, pyoderma) are not present. Antihistamines Antihistamines are not generally regarded as widely useful in the diagnosis or treatment of atopy. However, because skin testing is not widely available to the practitioner or is sometimes rejected by the client, a trial period of antihistamines may be indicated in certain patients as a limited diagnostic test and, if successful, as a subsequent palliative treatment. It is recommended to try a series of antihistamines such as diphenhydramine, chlorpheniramine, and hydroxyzine for a period of l week each to see if any is effective in limiting or controlling pruritus. It should be remembered that one of the side effects of antihistamines is increased sleepiness, which may account for any lessening of pruritus. Corticosteroids Corticosteroids tend to eliminate or lessen the pruritus of a wide variety of conditions. Therefore, they are generally not considered useful as a diagnostic tool. However, some conditions such as atopy, contact dermatitis, and endoparasitic migration are known to respond to antipruritic doses of corticosteroids (prednisone given at l mg per kg body weight). Most of the other pruritic conditions are only partially responsive to this dose. This crude test could be used when atopy is suspected and intradermal skin testing is not available.
SUMMARY Diagnosis of pruritic skin disease can be a time-consuming process. Careful attention must be paid to history, clinical examination, laboratory and clinical testing, methodical elimination of the differential diagnoses, and client communication in order to achieve success. REFERENCES l. August JR: Taking a dermatologic history. Compend Contin Ed Pract Vet 8:510--518, 1986 2. Griffin CE : Diagnostic approach to dermatologic disease. In Nesbitt GH (ed): Dermatology. New York, Churchill Livingstone, 1987, pp 1-19
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3. Muller GH, Kirk RW, Scott DW: Small Animal Dermatology. Edition 3. Philadelphia, WB Saunders Co, 1983 4. Reedy L: Pruritus in small animals. Compend Contin Ed Pract Vet 6:95-106, 1984 5. White SD: Mimicry in veterinary dermatology. In Proceedings of the American Animal Hospital Association, 1986, pp 178-179 Madera Pet Hospital 5796 Paradise Drive Corte Madera, California 94925
Pruritus
The Clinical Approach to the Pruritic Dog
Susan I. Reinke, DVM*
In approaching any dermatologic problem, a clinician must follow a systematic procedure to obtain the information necessary in establishing a correct diagnosis. Due to the similarity in the appearance of many skin diseases, usually one cannot take a cursory glance and then proceed to an appropriate therapeutic regimen that will yield long-term satisfactory results. Unfortunately, the handling of a dermatologic case is very time consuming. It is necessary to obtain a thorough history and perform a complete physical examination with special emphasis on the skin. Often in evaluating a chronic case, about one half of the office visit will be spent obtaining a complete and accurate history. The remaining time is divided between a complete physical examination, appropriate diagnostic tests, making a diagnosis or list of differential diagnoses, explaining the findings to the client, prescribing medication, and giving directions to the client regarding the therapeutic regimen that he or she is to follow.
HISTORY
Obtaining a complete history can help rule in or rule out many different diseases. It is very useful to have the client fill out a questionnaire regarding the dermatologic history prior to the examination. 1 The client has a chance to remember pertinent details and hopefully provide concise answers to such questions as "What do you feed your pet?" which can be very time consuming if asked orally. The veterinarian can then quickly go over the questionnaire and rephrase certain important questions to see that the answers have been a correct interpretation of what was being asked. Many times a client's perception or reporting of the facts is inaccurate, and approaching a subject from several different angles will improve accuracy. The client may have responded that the animal itches, but further ques*Diplomate, American College of Veterinary Dermatology; Staff Dermatologist, Madera Pet Hospital, Corte Madera, California Veterinary Clinics of North America: Small Animal Practice- Vol. 18, No. 5, September 1988
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tioning may reveal that the animal is pruritic for only a few minutes when it awakes each morning, a fairly common occurrence (in the author's experience) in many "normal" dogs. The clinician must be careful not to ask misleading questions so that a false emphasis results. When atopy or food allergy dermatitis is suspected, it is common to ask the client if the face and feet are pruritic. The client's positive response may mislead the veterinarian if the questioning does not also include frequency, what other areas are pruritic, and how the amount of pruritus in other ;:treas compares to the degree of facial/pedal pruritus. A dermatology history form may be obtained from Allerderm, Inc. (P.O. Drawer 277, Hurst, Texas 76053).
SIGNALMENT Age The signalment may provide important information. Some diseases characteristically begin at a certain range of ages. Food allergy has been reported to occur most commonly between 4 months and 4 years of age, 2 but in the author's experience it can occur at any age. Atopy most commonly develops from 2 to 4 years of age but may be seen from 1 to 8 years. Flea allergy may begin any time after 4 months of age. Allergy developing after age 8 is considered uncommon unless an older animal is moved from one area of the country to another, thus exposing the dog to a new group of potential allergens. Scabies, Cheyletiella, or dermatophytosis may be present in the very young dog coming from an infested kennel. Localized demodicosis occurs most commonly in the 3- to 6-month-old puppy. Generalized demodicosis, including demodicosis limited to the feet, can occur at any age. Endoparasitic migration, although rare, occurs in young puppies.
Breed Certain diseases tend to have a breed predilection such as the increased incide nce of atopy in the terrier breeds, Dalmatian, Irish Setter, Miniature Schnauzer, Boston Terrier, and Lhasa Apso. Pruritic superficial pyodermas (short-haired dog pyoderma) and pruritic interdigital dermatoses tend to occur in shorthaired breeds such as Boxers, Dalmatians, Dachshunds, Great Danes, Doberman Pinschers , Weimaraners, English Bulldogs, and Mastiffs. Breeds with deep cutaneous folds such as the Chinese Shar Pei, Pekingese, English Bulldog, and Pug tend to develop irritations in their skin folds that often are pruritic. Nasal pyodermas occur in long-nosed breeds such as the Collie, Doberman Pinscher, German Shepherd, and setter/retriever breeds. Acute, moist, pyotraumatic dermatitis (hot spots) occurs commonly in the Golden Retriever and Saint Bernard as well as other breeds. However, one has to be careful not to assume a diagnosis just because of the dog's breed. The underlying problem of all pruritic, seborrheic West Highland White Terriers or Cocker Spaniels is not necessarily their genes. These animals deserve a complete dermatologic workup before they are assigned to that discouraging category of idiopathic
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seborrhea and before one merely attempts to control a disease with a probable genetic basis. Sex The sex of the dog may also point to certain diseases related to each sex's respective sex hormones. It should be noted if females are spayed, cycling normally if not spayed, or are prone to having false pregnancies. Pruritic seborrheic conditions that respond to ovariohysterectomy are seen in females associated with cystic ovaries or functional ovarian tumors. Sexual characteristics such as normal interest in females, mounting behavior, and lifting the leg to urinate should be noted in the intact male. Functional Sertoli cell tumor with its classic clinical signs may be pruritic if seborrhea is present. Severe, pruritic, seborrheic skin disease is described (in addition to other clinical signs) in the so-called male feminizing syndrome. 3
HISTORY
Basic Problem The client should be asked to briefly describe what he or she views as the current problem-itching, hair loss, red bumps, and so on. An animal may present with multiple problems, yet the client is concerned about one of them and is only interested in pursuing that problem. A dog may present with an acute otitis that is concerning the owner, and he or she may be totally unconcerned and disinterested in the dog's chronic flea allergy. Successful treatment requires client cooperation and especially so in dermatologic cases that often require frequent medicated baths, dips, flea powdering, medicating, and so forth in order to achieve any degree of success. Otherwise; the veterinarian's carefully written instruction sheet along with the prescribed medications and shampoos may be disregarded. Because of the many secondary problems that can occur, it is important to try to determine the nature of the initial problem. The client should be asked to describe what the lesions originally looked like and where they began. Was there hair loss, redness, pimples, itching? Primary lesions may be obscured .in the chronic, pruritic dermatologic case by excoriation, crusts, lichenification, and hyperpigmentation. When presented with a dermatologic case, one of the first things to determine is the presence of pruritus by asking if the dog scratches, chews, rubs, or licks. Using these specific words is necessary when referring to pruritus because using only one may elicit answers that give a wrong impression- that is, if asked if the patient scratches, the owner may respond with a dear "no" and yet fail to add that the dog does chew or lick. The presence or absence of pruritus immediately classifies the condition into one of two basic categories of skin disease-pruritic and nonpruritic. However, it must be remembered that there can be "cross-overs" such as hypothyroidism, a usually nonpruritic endocrine disease, which when present with a secondary pyoderma may be very pruritic. Where did the dog begin itching? Where is it itchy now? (Later,
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during the physical examination, the client can actually point out the pruritic areas.) Does the dog scatch and chew enough to justify the degree of alopecia or did the hair seem to just fall out? A dog with obvious flea allergy dermatitis with excessive alopecia and seborrhea might also have concurrent hypothyroidism. The degree of pruritus needs to be established. When and how often does the pet scratch, chew, or lick? A situation in which a dog sleeps in the bedrool)) with an owner who is a light sleeper may elicit exaggerated complaints of severe pruritus. It is useful to describe a setting of the owner and the dog spending a quiet evenirig while the owner reads or watches television, and then ask how often and. with what ihterisity does the pet chew, scratch, rub, or lick the skin in a period of an hour. Another useful technique to aid in determining the degree of pruritus is to leave the dog loose on the examination room floor while the history is being obtained from the owner. The veterinarian can casually observe if the dog is pruritic enough to continue scratching even in the stress cif an examination room. Onset When did the problem begin? How old was the dog when it began? Did it begin after the dog was boarded during summer vacation, after an improperly diluted flea dip was applied, after a dry carpet cleaner was used in the house, after a new kitten was obtained from the pound? Was the onset . gradual or sudden? Acute pyotraumatic dermatitis, insect bite hypersensitivities, autoimmune disease, skin fold dermatitis, and nasal pyoderma in long-nosed breeds tend to develop rapidly. In addition, the owner rhay describe other conditions as having a very rapid onset when, in fact, the disease was present for some time but suddenly seemed much worse and of concern to the owner. For example, the alopecia and pruritus from flea allergy dermatitis might not garner much attention until a hot spot develops, seemingly overnight. Other diseases have a slower onset, with the symptomatology gradually building to a crescendo. The first year that atopy or flea allergy is symptomatic, the signs may be minimal, but in subsequent years, the signs may become more intense with a quicker onset during the "allergy" season. Did the dog have the problem when the owner first obtained it? Contagious diseases such as those caused by external parasites (fleas, Sarcoptes, Cheyletiella, Otodectes) and dermatophytes (Microsporum, Trichophyton) may be present in a breeding situation or humane soCiety where an animal may have originated. Has the condition occurred previously with any seasonality or periodicity? Diseases such as atopy, thrombiculiasis (chiggers), and fleas tend to be seasonal. The irritation and subsequent licking of the feet during the winter months where streets are icy and/or salted is a seasonal condition in cold weather climates. Also, some dogs tend to develop irritation and licking during rainy, moist seasons of the year when the interdigital areas are constantly moist. This can be further complicated by feet with long, thick interdigital hair.
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Clinical Progression How has the condition progressed? An observant owner may be able to trace the classic progression of superficial pyoderma from an erythematous papule to pustule to crusted papule to epidermal collarette with central hyperpigmentation. Pyodermas often occur secondary to pruritus. An observant client may be able to state that the papules and pustules that are present currently were not present when the pruritus began. An important but difficult-to-answer question when dealing with allergic disease is: Which came first, the itch or the rash? In allergic diseases such as atopy, pruritus precedes the skin lesions, whereas pruritis may occur just as the papules and pustules are forming in pyoderma. The owner may report that the disease was initially seasonal but now isn't. Atopy often begins as a spring/summer disease of short duration (6 to 8 weeks). As the years progress, the period of pruritus gradually lengthens until it may be year round. However, the sudden lengthening of a formerly short pruritic season should be viewed with caution. A secondary pruritic pyoderma or the development of an unrelated condition such as scabies may cause a regularly occurring 6-week seasonal duration of pruritus in an atopic dog to suddenly lengthen dramatically. In handling the continued care of any chronic dermatologic case, the clinician should always be alert to details that may indicate that this is not just another recurrence of the previously diagnosed condition. Heredity The role of heredity may be important. A client who casually mentions that her pet now smells just like its mother did should alert the veterinarian to direct attention to the family medical history. Certain diseases such as idiopathic seborrhea in the Cocker Spaniel, German Shepherd, Brittany Spaniel, and West Highland White Terrier tend to have a familial tendency. Generalized demodicosis and atopy are both regarded as hereditary diseases. Contagion What other animals live in the same household or visit with any regularity? Asking how many pets a client owns may not provide the kind of information needed when a client shares a dwelling with other people who also own pets. In flea-endemic areas, multi-pet households cause flea allergy dermatitis to be included on the differential list if the lesions and distribution pattern are at all suggestive, whether or not fleas or flea excrement are present on the dog. Are any of the other household animals scratching or do they have skin problems? Contagious conditions involving ectoparasites (Sarcoptes, Cheyletiella, Otodectes, fleas) or dermatophytosis may be present on the other housemates. However, the lack of skin disease in these other animals does not rule out contagious disease. Sarcoptic mange may occur in only one dog in a multi-pet household (asymptomatic carrier phenomenon). 3 Recent exposure to other animals should be investigated. Was the dog groomed, boarded, at a pet show, picked up by the pound, in someone else's home, or was there a recent canine visitor at its home?
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Do any of the people living in the household have skin lesions and/or itching? Flea bites tend to occur on the lower legs of people. Canine scabies and Cheyletiella mites may cause lesions on the arms, trunk, and under tight areas of clothing such as under elastic bands. Dermatophytosis lesions tend to be located on exposed areas of skin. Environment What is the pet's environment? Is it inside only, inside/outside, or outside only? Is it allowed to roam free? Does it regularly go to another home to be "dog-sat"? These questions are particularly important when considering flea allergy and when instructing the owner about flea control. Where is the dog during the day? Where and on what does it sleep? Knowledge of the dog's physical environment is important when considering contact dermatitis. Are the symptoms worse when the dog is inside or outside? Dogs allergic to trees, grasses, and weeds may be noticeably worse when outside; conversely, dogs allergic to house dust, feathers , tobacco, or wool may be worse inside. Are the other household pets inside or inside/outside animals? The current patient might be an inside pet, but there may be others who are allowed to go outside and bring fleas or other contagious disease back inside. Do other pets come to visit? Skin Hygiene and Flea Control The general skin care should also be considered. What shampoos, rinses, or deodorizers are used on the dog? Some of the most extraordinary preparations have been used in canine hygiene. In his or her determination to clear up a skin condition, a client may have greatly increased the concentration of fleas dips or applied strong products that further irritate the skin. How often is the dog bathed? When was the last bath? A recent bath may have removed evidence of fleas as well as scales and crusts. Is the dog better or worse after bathing? Seborrheic animals, in particular, seem to have some relief from pruritus following bathing. However, some severely allergic dogs with very erythematous skin are more pruritic after a bath. Specific questions regarding fleas and flea control are very important in flea-endemic areas. When did the client last see fleas? What type of flea control is used-shampoo, powder, spray, dip, collar, systemic insecticides? Is it oral or topical? How often is it applied? Is the same flea control used and as vigorously on the other unaffected household animals? Is environmental control used? Inside and outside? How often? What methods and what brands? Taking time to get complete answers to these questions and then following up with proper flea control education is of utmost importance in handling the dermatologic patient. In the author's experience, failure to consider the effects that a few fleas can cause leads to one of the more common reasons for dermatologic referrals. Diet When discussing the animal's diet, clients will often volunteer their opinion that the pruritus could not be from the food because the diet has
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been switched several times between various commercial brands. Or they say that it couldn't be the food because the dog has been on the same diet for months. Both comments are in error. Most commercial diets contain the same basic ingredients, so switching from one to another will not cause any improvement in the patient with food allergy. Most food allergies occur after the pet has been on the food for a period of months to 2 years. Drug History Drug eruption has been documented in the dog and always has to be considered if the pet has been on any type of medication not only in recent days but also in the past weeks to months. 3 Food additives need also to be considered as a source of drug eruption. Previous Dermatologic Treatment What drugs are currently being used? What drugs have been used in the past for the skin condition? What was the response? These questions are important and can be very time consuming unless the owner has filled out a history sheet and hopefully brought treatment information from previous veterinarians. Even then, laboriously reading through copies of someone else's records can be slow and frustrating. A brief summary of the dermatologic history containing pertinent diagnostic testing results and treatments given by the previous veterinarian is much more useful. It is usually expeditious if the client brings the various medications, shampoos, dips, and so forth to the office. The client can then point to the various products and comment on the response to them. The clinician can also note whether the medication was finished or that only 5 tablets out of 30 were missing from the bottle that "didn't work." Lack of client compliance may account for lack of response when the previous diagnosis and prescribed treatment seem appropriate. Knowledge of the specifics regarding previous corticosteroid and antibiotic therapy is important. Previous correct use of the appropriate antibiotics used to empirically treat pyodermas (lincomycin, clindamycin, erythromycin, oxacillin, chloramphenicol, trimethoprim-sulfa combinations, clavulonated amoxicillin, or cephalosporins) may alert the clinician that this apparent pyoderma may contain resistant organisms or may be one of the other pustular skin diseases (demodicosis, dermatophytosis, pemphigus, subcorneal pustular dermatosis, and so on). At this point, it might be best to culture and/or biopsy rather than just do cytology of the pustule contents and empirically choose an appropriate antibiotic. Conversely, noting that inappropriate antibiotics (ampicillin, tetracycline, penicillin) have been used for an apparent pyoderma will direct the clinician toward selection of a more appropriate empirical antibiotic. Also, an appropriate antibiotic may have been chosen to treat an apparent pyoderma, but the previous veterinarian may have used an incorrect dosage or prescribed it for an inadequate length of time. In recurring pyodermas, the client may report that the drug did not work. On closer questioning, the truth may be that the lesions disappeared while the animal was taking the drug but recurred sometime after the antibiotic was withdrawn. Or the lesions may have disappeared, but the pruritus was still significant. Pursuing tests for
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underlying causes of pyoderma such as hypothyroidism and allergic disease as well as educating the client to the problem of pyoderma recurrence will yield better long-term results than just selecting another antibiotic. Dates of administration and dosages of corticosteroids in the last year should be obtained if possible. This knowledge is necessary for planning intradermal skin testing for inhaled allergies because long withdrawal periods may be necessary for the animal on continuous corticosteroid therapy. Also, recent corticosteroid use may have altered the lesions, resulting in an inaccurate picture of the true disease. The animal's response to previous corticosteroid therapy should be noted. Was the response complete or incomplete? How did the lesions and the amount and degree of scratching and so forth change during and after the therapy? Some conditions, such as atopy and contact dermatitis, may be completely responsive to minimal doses of corticosteroids (prednisone given at 1 mg per kg body weight). In other common conditions, such as flea allergy and pyoderma, the pruritus may be only decreased. In addition, the lesions of such diseases as pyoderma are usually still present even though slightly improved in appearance. Questions on previous therapy should also include what type of home therapy has been used on the pet and with what success. Tactful, nonjudgmental questions are always desirable, but they are apt to be especially rewarding here. It can be embarrassing for a client to admit some of the - home remedies that have been tried, especially if the dog's condition became worse after their use.
PHYSICAL EXAMINATION It is desirable to request that the client refrain from bathing the dog and stop all medications (except heartworm preventative, thyroid supplementation, and cardiac drugs) 2 weeks prior to the examination in order to present the condition in its most natural state. A routine physical examination should be performed and correlations determined, if they exist, between any abnormalities and the findings of the subsequent dermatologic examination. A thorough and systematic dermatologic examination, performed in adequate lighting, is mandatory. The general condition of the coat and skin should be noted. Is the hair shiny? Is the hair of normal thickness, texture, and length? Is the skin smooth and of normal thickness and elasticity, or is it greasy or excessively dry and scaly? Does the hair epilate easily? Easily epilated hair is associated with endocrine skin diseases but may also occur in localized areas as a result of excoriation and/or inflammation. A general distribution pattern of lesions should be noted. The client at this time can point out the pruritic areas and be questioned specifically as to the predominant areas of pruritus. Then a systematic examination can begin, usually starting with the head and proceeding distally, emphasizing the ears, ear margins, mucocutaneous junctions, mucosa, all aspects of the feet, nails and pads, genitalia, and lymph nodes. Going against the lay of the hair with the fingers may allow
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adequate visualization of the skin and hair, but shaving small areas may be necessary in heavily haired animals. It is essential for the clinician to become familiar with the different types of morphologic lesions and be able to recognize both primary and secondary lesions and what they represent. Primary lesions occur as the direct result of the disease process. Secondary lesions are a result of self~ trauma or of the progression of primary lesions. Failure to recognize that a papule might represent folliculitis and failure to identify epidermal collarettes are two common mistakes made by practitioners. Superficial pyodermas, which may be represented by papules, crusted papules, and epidermal collarettes and located on the ventral-lateral trunk, are very common in pn.iribc animals. The challenge then becomes to determine whether the pyoderma is secondary to a pruritic condition and only contributing to the pruritus or whether it is a primary condition that will respond fully to . antibiotic therapy. A progression of lesions may be present on the animal, which may help the clinician diagnostically. Papules often progress to pustules that rupture to leave an erosion. A crust forms, and eventually an epidermal collarette with subsequent central hyperpigmentation is evident. Lesions should be closely examined for their relationship to hair follicles. A papule with a hair emerging froin the center indicates a folliculitis for which the etiology will have to be determined. Distribution Pattern The distribution pattern is very important in ruling in or ruling out various pruritic diseases. Is it generalized or localized or occurring in specific regions such as the ventral abdomen? Symmetric or asymmetric? Symmetric lesions are not necessarily the classic indication of hormonal disease but can occur in allergic, ectoparasitic, and autoimmune diseases. 2 Many skin diseases have a characteristic distribution pattern of lesions and/or pruritus. Noting the pattern in conjunction with the history and types of lesions may lead to at least a list of differential diagnoses if not the diagnosis itself. Generalized Pruritus Many conditions may present with generalized pruritus or as generalized pruritus with emphasis in certain areas. The parasitic diseases [sarcoptic, demodectic, Cheyletiella mange; flea allergy dermatitis, thrombiculiasis (chiggers), pelode ra dermatitis, e ndoparasitic migration in puppies] may be generalized. However, the lesions and pruritus of sarcoptic mange tend to be concentrated on the ears and ear margins, elbows, and ventral thorax. Demodectic marlge usually begins on the head. The predominant areas of flea allergy dermatitis tend to be the lumbosacraVtail head/posteromedial aspects of the rear legs. Chiggers are usualiy found on the face, ears, and head but can also be found on the ventral body surfaces. Pelodera terids to cause pruritus in areas where the ground and skin come into contact. Pyodermas may be locaiized or generalized. Skin-fold pyodermas and the lesions of acute pyotraumatic dermatitis are usually localized. Superficial pruritic pyodermas may be generalized but most commonly occur along
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the ventral lateral trunk. Deep pyodermas have a similar distribution pattern that may also include the feet, legs, and face. Affected dogs tend to lick their feet, which may be a manifestation of pain and/or pruritus. Dogs with food allergy dermatitis may have generalized to regionally localized pruritus with erythema and papules, or the condition may mimic diseases such as flea allergy dermatitis, seborrhea, recurrent moist, pyotraumatic dermatitis, and otitis externa. 3 Dogs with atopy may present with generalized pruritus or with a facial/pedal/ventral distribution pattern. Contact dermatitis may be generalized if the irritant has been directly applied to the dog or localized if it is something in which the dog has been lying or walking. Autoimmune diseases may be pruritic and generalized, often having lesions on the head with some mucocutaneous orientation. Dogs with seborrhea often present with generalized pruritus. The lesions and pruritus tend to be more severe in fold and intertriginous areas, particularly neck folds, cranial tarsal areas, interdigital areas, and axillae. These animals often have a secondary superficial pyoderma. Treatment with appropriate antibiotics arid frequent shampooing will often alleviate much of the discomfort, odor, and lesions of a chronic seborrhea of unknown etiology. Several endocrine-related dermatoses may be associated with generalized, or at least regional, pruritus. The pruritus in these traditionally nonpruritic diseases is usually due to seborrheic changes or secondary pyoderma. Hypothyroidism may present with seborrhea and/or pyoderma, - both of which may be pruritic. So-called type I ovarian imbalance in unspayed females may have generalized seborrhea arid/or seborrhea with licheq.ificatibn and hyperpigmentation of the perivulvar area. 3 Functional Sertoli cell tumors may be pruritic if sufficient seborrhea is present. Socalled male feminizing syndrome (which may actually be due to a nondiagnosed Sertoli cell tumor) presents with seborrhea and pruritus. 3 Calcinosis cutis (calcium deposits in the skin) that can occur with hyperadrenocorticism (Cushing's disease) tends to occur on the trunk and can be very pruritic, particularly when secondarily infected. Mycosis fungoides, a T-cell lymphocytic neoplasia of the skin, may begin as a generalized, erythematous, scaling pruritic condition. It progresses to plaque and nodular stages. Mastocytomas, especially when diffuse, may produce marked pruritus. 4 Other cutaneous neoplasms or cysts are not generally regarded as pruritic, although at times a dog may scratch or chew at them. Facial Pruritus Demodectic mange (sometimes pruritic), sarcoptic rriange, atopy, and food allergy usually present with facial lesions and/or pruritus. Contact dermatitis, especially of the muzzle region, can occur through rooting or contact with certain vinyl food dishes (rarely seen in recent years). The autoimmune diseases (pemphigus, pemphigoid, lupus erythematosus) often begin ori the head and rriay be pruritic. Breeds with prominent facial folds may have pruritic irritations in those areas either as a continual problem or sporadically. Diseases of the eyelid margins may lead to pruritus related to the orbital and periorbital area.
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Long-nosed breeds may present with a relatively acute onset of lesions on the bridge of the nose including erythema, scaling, papules to crusted papules, alopecia, excoriation, erosion, and ulceration. The differential diagnoses to consider are demodicosis, dermatophytosis, nasal pyoderma; autoimmune disease (pemphigus and lupus erythematosus), and acute insect bite hypersensitivity. Nasal solar dermatitis was previously considered a differential diagnosis, but recently most biopsies of these cases have been diagnosed histologically as lupus erythematosus. Foreign bodies of the mouth, nose, eye, and ear should also be considered in any acute onset of facial rubbing, scratching, or pawing. Pinnal Pruritus Pruritus of the pinnae may occur in atopy and food allergy, contact allergy from an otic preparation, chiggers, and fly strike. Sarcoptic mange classically involves the pinnae, especially the margins, but similar scaling and crusting of the pinnal margin can occur in certain dogs with seborrhea, particularly spaniel-type breeds. Leishmaniasis, not normally a pruritic disease, may present with slightly pruritic, excoriated, nodular lesions on the pinnae (as well as the typical scaling lesions of the ears, face , pressure points, and/or entire body.) Diseases of the external ear canal, of course, may cause localized scratching and rubbing with resultant excoriation and alopecia of the pinnae. Pedal Pruritus When a dog is presented with pruritus and/or lesions related to the feet, a skin scraping is mandatory to rule out demodectic mange. Other conditions to consider in the differential diagnosis of pedal pruritus are atopy, food allergy dermatitis, allergic or irritant contact dermatitis, interdigital pyoderma, sterile interdigital pyogranuloma, autoimmune disease, Pelodera dermatitis, foreign bodies, and other digital and interdigital inflammatory diseases. Some dogs, especially Poodles and Miniature Schnauzers, tend to display neurotic licking of one or more feet. FaCial/Pedal Pruritus Facial/pedal (with often axillary or generalized) pruritus is commonly associated with atopy and food allergy. The dog may rub its muzzle and/or scratch at the face and ears. Caution must be exercised in interpreting client's reports of facial rubbing. Frequency is important. It is the author's observation that some dogs normally rub their faces after eating. The allergic animal will usually have signs of excoriation and alopecia involving the periocular, pe rioral, and pinnal areas. Lumbosacral and Tailhead Pruritus In appropriate climates, lumbosacral and tailhead pruritus, alopecia, and excoriation are classically interpreted as flea allergy dermatitis. However, this distribution pattern has also been seen in atopy and food allergy dermatitis. 5
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Axillary and Inguinal Pruritus Pruritic diseases commonly involving the axillary/inguinal regions are flea allergy dermatitis, sarcoptic mange, pyoderma (superficial and deep), atopy, food allergy, and contact dermatitis. Most of these diseases, of course, present with pruritus and lesions elsewhere on the body. DIFFERENTIAL DIAGNOSES After the history and physical examination are completed, a list of differential diagnoses should be made. By careful consideration of the information now at hand, the clinician can hopefully limit this list to a reasonable, workable number. Unfortunately, it is often not possible to make an absolute diagnosis without having to resort to differential diagnoses and diagnostic testing to rule in or rule out each diagnosis. In order to gain the client's confidence and cooperation, the clinician must now explain why this is the appropriate approach to making a dermatologic diagnosis. It is helpful to say that the skin can only respond in a certain number of ways (it can become erythematous, scaly, papular/pustular, and so on), and many different diseases can cause each of those signs. Therefore, a certain number of tests are required to (hopefully) reach a diagnosis through the systematic process of eliminating the various differential diagnoses. Depending on the ease of future visits (due to distance travelled or job requirements), financial limitations, severity and chronicity of the condition, client motivation and frustration, the tests may be completed at the first visit; more likely, a tiine table will be set up, and tests for the more likely diseases will be scheduled first. If the results are negative, further testing can then be scheduled. Unfortunately, in the general practice situation, many clients are unwilling to pursue a diagnosis involving many tests. Many tiines, the general practitioner is faced with "Oh, just give him a cortisone shot, Doc." When the veterinarian is faced with lack of interest for diagnostic testing, the client will often accept trial therapy, which will be discussed later. Trial therapy is important in the elimination of several important differential diagnoses of pruritic canine skin disease. DIAGNOSTIC TESTING Skin Scraping and Fungal Culture In the majority of cases, the mm1mum database includes properly performed skin scrapings and fungal culture. Wood's light examination is fraught with so many false-positives that it should not be done unless a fungal culture is done concurrently. Even in the hands of experienced mycologists, potassium hydroxide preparations of hair shafts are considered very difficult to evaluate for evidence of dermatophytes. Cytology and Bacterial Culture and Sensitivity
If a vesicle or pustule is present, cytologic examination of the contents smeared on a glass slide and stained with an appropriate stain such as Diff
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Quik should be made. Rod or coccoid bacteria can be visualized as well as types of white blood cells. Bacteria located within white blood cells is an indication that the bacteria seen are part of a disease process and are not just bystanders. Also it is an indication that at least one part of the immune system (phagocytosis) is functioning. Significant numbers of acantholytic cells (large, rounded, dark-staining epithelial cells) are indicative of pemphigus. Cytology is a more appropriate test than bacterial culture and sensitivity in the initial presentation of a pustular disease. Because the vast majority of canine pyodermas are caused by coagulase-positive Staphylococcus species, the presence of cocci in the smear will direct the clinician towards choosing one of the several known effective drugs against Staphylococcus species. If a mixed bacterial population is seen or if the pustular disease is recurrent or nonresponsive to antibiotics or is a deep pyoderma, a bacterial culture and sensitivity are indicated. Blood Screens A chemical profile and/or complete blood count may be indicated if systemic illness or endocrine disease is suspected. A minimum level of 1,000 lymphocytes per ml is considered necessary for basic immune competence. These blood tests are often overused in the dermatologic patient. The client's money is often better spent on other tests or trial therapies. Thyroid and adrenal evaluation may be performed at the initial visit if the clinical signs are indicative. The antinuclear antibody test may be performed when autoimmune disease is suspected. Biopsy Biopsy for routine histologic examination is usually not one of the initial tests performed unless the lesions appear to be something that the clinician has never seen before, a diagnosed condition not responding to appropriate therapy, a suspected neoplasia, or a suspected autoimmune disease. Although they do not always provide a diagnosis, the results can often rule out some of the proposed differential diagnoses. Taking multiple sections of primary lesions is preferred. If autoimmune disease is suspected, a section should be saved in Michele's medium for immunofluorescent testing. Biopsying appropriate lesions and providing adequate history and physical examination findings to the histopathologist will result in much more useful information. Also, care should be taken in selecting a histopathologist. A veterinary dermatopathologist, a dermatologist with special training in dermatopathology, or a general veterinary pathologist with special interest in the skin is preferred. A discussion of biopsy techniques as well as pertinent information on other diagnostic tests is available in various veterinary texts. 2· 3 Skin Testing Intradermal skin testing for atopy is best performed by a specialist or other clinician seeing enough dermatologic cases to enable frequent testing. Intradermal skin testing has an element of art as well as science that is best developed with frequent practice. As a general practice, this test is often
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performed after other differential diagnoses have been ruled out unless the history and clinical signs are classic for this condition.
TRIAL THERAPY Response to therapy can be an important method of ruling in or ruling out various differential diagnoses. It is also one type of "test" that usually has good client acceptance. However, the client must be educated as to what changes he or she is to observe from the trial therapy, such as healing of lesions and cessation of pruritus. The client must also be aware of what to watch for once the trial therapy is discontinued. Paracitacidals Response to paracitacidals is almost always included as a diagnostic consideration in flea-endemic climates. A full explanation of the steps necessary to control fleas on all the household animals as well as the pet's environment is essential in ruling out fleas as a source of pruritus. Client cooperation can be best obtained by explaining that all possible sources of pruritus must be eliminated, the most obvious of which is often fleas. Often the client is anxious to go on to more "glamorous" etiologies of pruritus. It must be explained, for example, that it is impossible to know if the dog is responding to a food elimination diet that is manifested by decreased pruritus if fleas, which are known to cause pruritus, are still on the dog. A client will often agree to a set period of time such as 3 to 4 weeks for doing maximum flea control as a "flea allergy test." Because sarcoptic mange is difficult to diagnose via skin scraping, it is often diagnosed in retrospect after a positive response to appropriate paracitacidals (lime sulfur, amitraz, ivermectin, certain organophosphates). Antibiotics Pyoderma is one of the most underdiagnosed conditions in veterinary dermatology. When presented with a papular or crusted papular condition, a trial period of an appropriate empirically chosen antibiotic may be indicated. Having the client closely observe the pet during and after the antibiotic treatment may help determine not only if the lesions are antibiotic responsive and thus probably a pyoderma but also whether the pyoderma is a pruritic pyoderma or a pyoderma that has occurred secondary to pruritus from another condition. In the first instance, the pruritus will disappear as the lesions heal. In the second, the pruritus will persist even after the lesions are healed. It could be argued that biopsy is a more reliable method of diagnosing pyoderma. Perhaps that is true, but the use of antibiotics answers two questions: Are the lesions antibiotic responsive and is the pruritus antibiotic responsive? In addition, a trial period of antibiotic treatment is generally less expensive than biopsying. Also, it is sometimes difficult to locate an appropriate lesion that will result in a clear-cut diagnosis.
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Food Elimination Diet The only accepted method for diagnosing food allergy dermatitis is with a specific food elimination diet. A 3-week diet consisting of lamb and brown rice or potatoes is commonly used. The client must be instructed to observe the level of pruritus while the animal is on the diet as well as when the diet is terminated. Care must be taken to be sure that other concurrent sources of pruritus (fleas, pyoderma) are not present. Antihistamines Antihistamines are not generally regarded as widely useful in the diagnosis or treatment of atopy. However, because skin testing is not widely available to the practitioner or is sometimes rejected by the client, a trial period of antihistamines may be indicated in certain patients as a limited diagnostic test and, if successful, as a subsequent palliative treatment. It is recommended to try a series of antihistamines such as diphenhydramine, chlorpheniramine, and hydroxyzine for a period of l week each to see if any is effective in limiting or controlling pruritus. It should be remembered that one of the side effects of antihistamines is increased sleepiness, which may account for any lessening of pruritus. Corticosteroids Corticosteroids tend to eliminate or lessen the pruritus of a wide variety of conditions. Therefore, they are generally not considered useful as a diagnostic tool. However, some conditions such as atopy, contact dermatitis, and endoparasitic migration are known to respond to antipruritic doses of corticosteroids (prednisone given at l mg per kg body weight). Most of the other pruritic conditions are only partially responsive to this dose. This crude test could be used when atopy is suspected and intradermal skin testing is not available.
SUMMARY Diagnosis of pruritic skin disease can be a time-consuming process. Careful attention must be paid to history, clinical examination, laboratory and clinical testing, methodical elimination of the differential diagnoses, and client communication in order to achieve success. REFERENCES l. August JR: Taking a dermatologic history. Compend Contin Ed Pract Vet 8:510--518, 1986 2. Griffin CE : Diagnostic approach to dermatologic disease. In Nesbitt GH (ed): Dermatology. New York, Churchill Livingstone, 1987, pp 1-19
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3. Muller GH, Kirk RW, Scott DW: Small Animal Dermatology. Edition 3. Philadelphia, WB Saunders Co, 1983 4. Reedy L: Pruritus in small animals. Compend Contin Ed Pract Vet 6:95-106, 1984 5. White SD: Mimicry in veterinary dermatology. In Proceedings of the American Animal Hospital Association, 1986, pp 178-179 Madera Pet Hospital 5796 Paradise Drive Corte Madera, California 94925