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Causes of Canine External Otitis
PA G E 4
A D VA N C E S
CAUSES OF CANINE EXTERNAL OTITIS Background Otitis externa in the dog is among the most common medical disorders in the dog. Causative factors of external otitis are classified as predisposing, primary, secondary, and perpetuating. Predisposing factors, such as ear conformation, increased moisture, trauma, and obstruction increase the risk. Primary causes, such as ectoparasites, foreign bodies, allergies, and keratinization disorders, initiate ear canal inflammation that is subsequently
A D VA N C E S
intensified by secondary factors (bacterial and yeast infections). Perpetuating factors are progressive pathological changes of the ear canal, tympanic membrane, and middle ear due to chronic inflammation. Successful treatment of external otitis requires identification and elimination of all causative factors. Elimination of predisposing, primary, and secondary causes are necessary for acute and chronic diseases. Chronic or recurrent external otitis must also have perpetuating factors eliminated.
factors. Ear canal stenosis (38% of dogs) and tympanic membrane perforation-otitis media (25%) were the most frequent perpetuating factors. Atopic dermatitis and adverse food reactions-associated external otitis were more common in females and dogs with pruritus. Grass awn-induced external otitis occurred in cocker spaniels and acute cases. Cocci overgrowth was positively associated with ear canal stenosis.
Author Conclusion Objectives To investigate the possible associations between signalment, history, clinical and laboratory findings and the various primary, secondary, and perpetuating causative factors of external otitis.
Procedure The medical records of 100 dogs with external otitis were reviewed irrespective of whether it was a primary or secondary complaint or just discovered during the physical examination. The review of dogs’ histories involved gathering information on signalment, the dog’s type of home environment, the primary purpose of the dog, its contact with other dogs or cats, the chance of water entering the ear canal from swimming or bathing, and the presence of pruritus on other areas of the body than the ears. Review of the physical findings included whether unilateral or bilateral external otitis was found and finding of the various primary, secondary, and perpetuating factors. Otitis externa less than 2 months in duration was considered acute. Durations of more than 2 months or more than 1 episode per year were categorized as chronic-recurrent.
Results Dogs were affected between 3 months to 14 years of age with a median of 4.75 years. Gender distribution was 45 males and 55 females. Cocker spaniels, Jura des Alpes, and Brittany spaniels were significantly at higher than average risk. External otitis was most commonly chronic-recurrent (63%) or bilateral (93%). Allergic dermatitis (43% of dogs), grass awns (12%), and otoacariasis (7%) were the most common primary causative factors. A primary cause was not found in 32 cases, but more than 1 cause was found in 3 dogs. Malassezia yeasts (66% of dogs), cocci (38%), and rods (22%) were the secondary causative
There is a higher incidence of atopic dermatitis and adverse food reactionsassociated external otitis in females and in dogs with pruritic skin disease. Grass awn-induced external otitis is found more frequently in cocker spaniels and acute cases. Tympanic membrane perforation is negatively associated with atopic dermatitis or adverse food reactions-associated external otitis and positively associated with the presence of grass awns and rods. A positive association exists between cocci overgrowth and ear canal stenosis.
Inclusions One table, 33 references.
Editor Annotation Otitis externa is very common in clinical practice. It is important to identify all the factors contributing to development of otitis externa in a patient. The authors of this report evaluated 100 dogs to look for associations between signalment, history, clinical and laboratory findings, and the various causes of ear inflammation. They classified factors into 1 of 4 categories: predisposing, primary, secondary, and perpetuating. Predisposing causes are factors such as conformation of the ear pinnae and ear canal, moisture from swimming, bathing or high environmental humidity, and trauma which increase the risk for otitis but do not cause it directly. Primary causes (ectoparasites, foreign bodies, allergies, keratinization disorders, immune-mediated diseases, and drug reactions) can initiate inflammation of the ear canals. Secondary factors include bacterial and yeast infections that intensify inflammation. Perpetuating factors include progressive hyperplasia of the epithelium of the ear canal, mineralization of cartilage, loss of epithelial migration, and otitis media. Many other classification schemes include bacterial and yeast infec-
PAG E 5
tions as perpetuating factors instead of secondary factors. Regardless of the classification scheme adopted, each of these factors needs to be evaluated and corrected, if possible. This study found cocker spaniels, Jura des Alpes, and Brittany spaniels as the breeds with highest risk of developing otitis externa. Cocker spaniels have also been reported at increased risk in other studies. Cocker spaniels lead the list as the most common breed to be referred to specialists for evaluation of otitis externa because of their propensity to develop marked hyperplasia of ceruminous gland hyperplasia-ectasia, which perpetuates ear inflammation, resulting in chronic or recurrent otitis externa. In the present study, Cocker spaniels had a high incidence of grass awns which may be due to trapping of grass awns in the hair of their large hanging ear pinnae. This study found an association between the presence of cocci on ear cytology and ear canal stenosis. This suggests that aggressive therapy with both corticosteroids and antibiotics may be warranted for patients with cocci on ear cytology. Gram-negative organisms were associated with the presence of grass awns. Thus, it is particularly important to do a thorough otoscopic examination for grass awns when gram negative organisms are found on ear cytology. Additionally, gram negative organisms were associated with ear canal ulceration and perforation of the tympanic membrane. This may be due to proteases produced by these bacteria. It may be wise to avoid the use of agents with high potential for ototoxicity when gram-negative agents are identified on ear cytology. Nearly half of the dogs in this study (43 of 100 dogs) had a history of pruritic dermatitis. This study found that allergies were more common in female dogs and that the dogs with allergic causes of otitis externa had a lower incidence of tympanic membrane rupture. However, the diagnosis of allergic dermatitis was only confirmed in 10 dogs (8 with atopy and 2 with food allergies) despite a presumptive diagnosis of allergies in 33 other dogs. (KLC) Saridomichelakis MN, Farmaki R, Leontides LS, et al. Aetiology of canine otitis externa: a retrospective study of 100 cases. Vet Derm 2007;18:341-347.
A D VA N C E S
CAUSES OF CANINE EXTERNAL OTITIS Background Otitis externa in the dog is among the most common medical disorders in the dog. Causative factors of external otitis are classified as predisposing, primary, secondary, and perpetuating. Predisposing factors, such as ear conformation, increased moisture, trauma, and obstruction increase the risk. Primary causes, such as ectoparasites, foreign bodies, allergies, and keratinization disorders, initiate ear canal inflammation that is subsequently
A D VA N C E S
intensified by secondary factors (bacterial and yeast infections). Perpetuating factors are progressive pathological changes of the ear canal, tympanic membrane, and middle ear due to chronic inflammation. Successful treatment of external otitis requires identification and elimination of all causative factors. Elimination of predisposing, primary, and secondary causes are necessary for acute and chronic diseases. Chronic or recurrent external otitis must also have perpetuating factors eliminated.
factors. Ear canal stenosis (38% of dogs) and tympanic membrane perforation-otitis media (25%) were the most frequent perpetuating factors. Atopic dermatitis and adverse food reactions-associated external otitis were more common in females and dogs with pruritus. Grass awn-induced external otitis occurred in cocker spaniels and acute cases. Cocci overgrowth was positively associated with ear canal stenosis.
Author Conclusion Objectives To investigate the possible associations between signalment, history, clinical and laboratory findings and the various primary, secondary, and perpetuating causative factors of external otitis.
Procedure The medical records of 100 dogs with external otitis were reviewed irrespective of whether it was a primary or secondary complaint or just discovered during the physical examination. The review of dogs’ histories involved gathering information on signalment, the dog’s type of home environment, the primary purpose of the dog, its contact with other dogs or cats, the chance of water entering the ear canal from swimming or bathing, and the presence of pruritus on other areas of the body than the ears. Review of the physical findings included whether unilateral or bilateral external otitis was found and finding of the various primary, secondary, and perpetuating factors. Otitis externa less than 2 months in duration was considered acute. Durations of more than 2 months or more than 1 episode per year were categorized as chronic-recurrent.
Results Dogs were affected between 3 months to 14 years of age with a median of 4.75 years. Gender distribution was 45 males and 55 females. Cocker spaniels, Jura des Alpes, and Brittany spaniels were significantly at higher than average risk. External otitis was most commonly chronic-recurrent (63%) or bilateral (93%). Allergic dermatitis (43% of dogs), grass awns (12%), and otoacariasis (7%) were the most common primary causative factors. A primary cause was not found in 32 cases, but more than 1 cause was found in 3 dogs. Malassezia yeasts (66% of dogs), cocci (38%), and rods (22%) were the secondary causative
There is a higher incidence of atopic dermatitis and adverse food reactionsassociated external otitis in females and in dogs with pruritic skin disease. Grass awn-induced external otitis is found more frequently in cocker spaniels and acute cases. Tympanic membrane perforation is negatively associated with atopic dermatitis or adverse food reactions-associated external otitis and positively associated with the presence of grass awns and rods. A positive association exists between cocci overgrowth and ear canal stenosis.
Inclusions One table, 33 references.
Editor Annotation Otitis externa is very common in clinical practice. It is important to identify all the factors contributing to development of otitis externa in a patient. The authors of this report evaluated 100 dogs to look for associations between signalment, history, clinical and laboratory findings, and the various causes of ear inflammation. They classified factors into 1 of 4 categories: predisposing, primary, secondary, and perpetuating. Predisposing causes are factors such as conformation of the ear pinnae and ear canal, moisture from swimming, bathing or high environmental humidity, and trauma which increase the risk for otitis but do not cause it directly. Primary causes (ectoparasites, foreign bodies, allergies, keratinization disorders, immune-mediated diseases, and drug reactions) can initiate inflammation of the ear canals. Secondary factors include bacterial and yeast infections that intensify inflammation. Perpetuating factors include progressive hyperplasia of the epithelium of the ear canal, mineralization of cartilage, loss of epithelial migration, and otitis media. Many other classification schemes include bacterial and yeast infec-
PAG E 5
tions as perpetuating factors instead of secondary factors. Regardless of the classification scheme adopted, each of these factors needs to be evaluated and corrected, if possible. This study found cocker spaniels, Jura des Alpes, and Brittany spaniels as the breeds with highest risk of developing otitis externa. Cocker spaniels have also been reported at increased risk in other studies. Cocker spaniels lead the list as the most common breed to be referred to specialists for evaluation of otitis externa because of their propensity to develop marked hyperplasia of ceruminous gland hyperplasia-ectasia, which perpetuates ear inflammation, resulting in chronic or recurrent otitis externa. In the present study, Cocker spaniels had a high incidence of grass awns which may be due to trapping of grass awns in the hair of their large hanging ear pinnae. This study found an association between the presence of cocci on ear cytology and ear canal stenosis. This suggests that aggressive therapy with both corticosteroids and antibiotics may be warranted for patients with cocci on ear cytology. Gram-negative organisms were associated with the presence of grass awns. Thus, it is particularly important to do a thorough otoscopic examination for grass awns when gram negative organisms are found on ear cytology. Additionally, gram negative organisms were associated with ear canal ulceration and perforation of the tympanic membrane. This may be due to proteases produced by these bacteria. It may be wise to avoid the use of agents with high potential for ototoxicity when gram-negative agents are identified on ear cytology. Nearly half of the dogs in this study (43 of 100 dogs) had a history of pruritic dermatitis. This study found that allergies were more common in female dogs and that the dogs with allergic causes of otitis externa had a lower incidence of tympanic membrane rupture. However, the diagnosis of allergic dermatitis was only confirmed in 10 dogs (8 with atopy and 2 with food allergies) despite a presumptive diagnosis of allergies in 33 other dogs. (KLC) Saridomichelakis MN, Farmaki R, Leontides LS, et al. Aetiology of canine otitis externa: a retrospective study of 100 cases. Vet Derm 2007;18:341-347.