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radiography of joints as ancillary aids to clinical diagnosis and treatment in small ruminant practice
Small Ruminant Research 110 (2013) 82–87
Contents lists available at SciVerse ScienceDirect
Small Ruminant Research journal homepage: www.elsevier.com/locate/smallrumres
Analysis of samples of cerebrospinal fluid, thoracic ultrasonography and arthrocentesis/radiography of joints as ancillary aids to clinical diagnosis and treatment in small ruminant practice夽 P.R. Scott University of Edinburgh, Royal (Dick) School of Veterinary Studies, Easter Bush Veterinary Centre, Roslin, Midlothian, United Kingdom
a r t i c l e
i n f o
Article history: Available online 11 December 2012 Keywords: Arthritis Cerebrospinal fluid Radiography Respiratory disease Sheep Ultrasonography
a b s t r a c t Two useful ancillary tests for the busy small ruminant practitioner are analysis of samples of lumbar cerebrospinal fluid, collected from unusual and/or problematic cases, and thoracic ultrasonography in suspected chronic respiratory disease of adult sheep. In contrast, arthrocentesis and radiography of joint lesions in adult sheep can prove misleading and should be interpreted with caution. © 2012 Elsevier B.V. All rights reserved.
1. Introduction There is a wide range of ancillary aids that can be employed by the small ruminant practitioner, to help confirm the provisional diagnosis reached during the clinical examination. This article reviews those clinical presentations, where analysis of samples of cerebrospinal fluid, thoracic ultrasonography and arthrocentesis/radiography of joints may prove useful in clinical practice. 2. Collection and analysis of cerebrospinal fluid samples Collection and analysis of lumbar cerebrospinal fluid samples is particularly useful to confirm the presence of an inflammatory lesion involving the leptomeninges, such as bacterial meningo-encephalitis, and to investigate potential compressive lesions of the spinal cord (Fig. 1) and less
夽 This paper is part of the special issue entitled “Lectures of the 1st European Conference on Small Ruminant Health Management”, held in Athens, Greece, October 2011. Guest Edited by G.C. Fthenakis. E-mail address: [email protected] 0921-4488/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.smallrumres.2012.11.009
common neurological conditions (e.g., sarcocystosis; Fig. 2) (Scott, 1992, 2004, 2010a). 2.1. Method for sample collection Collection of lumbar cerebrospinal fluid (CSF) is facilitated when the sheep is positioned in sternal recumbency, with the hips flexed and the pelvic limbs extended alongside the abdomen. The sheep’s head is averted against the animal’s flank (Scott, 1993a, 1994). Sedation of the animal is not usually necessary, but intramuscular xylazine (0.05 mg kg−1 bodyweight) or diazepam (0.04 mg kg−1 bodyweight) can be used to aid restraint and facilitate positioning of the animal. The site for lumbar CSF collection is the midpoint of the lumbosacral space identified as the midline depression between the last palpable dorsal lumbar spine (L6) and the first palpable sacral dorsal spine (S2). This site is approximately 1–2 cm caudal to an imaginary line joining the wings of the ilium. The needle is slowly advanced over 10 s at a right angle to the plane of the vertebral column or with the hub directed 5–10◦ caudally. It is essential to appreciate the changes in tissue resistance as the needle
P.R. Scott / Small Ruminant Research 110 (2013) 82–87
Fig. 1. Lumbar cerebrospinal fluid collection is particularly useful in the investigation of compressive lesions of the spinal cord.
point passes sequentially through the subcutaneous tissue, interarcuate ligament then the sudden ‘pop’, due to the loss of resistance as the needle point exits the ligamentum flavum into the extradural space. Once the needle has been advanced fractionally further and its point has penetrated the dorsal subarachnoid space, CSF will well up in the needle hub within 2–3 s. A CSF quantity of 1–2 mL is sufficient for laboratory analysis and, although the sample can be collected by free flow over 1–2 min, it is more convenient to employ very gentle syringe aspiration over 20 s. There is no justification to collect from the ventral subarachnoid space. 2.2. Analysis Cerebrospinal fluid is clear and colourless. It is noteworthy that agitation of the sample will cause damage to cell morphology. Stable foam is indicative of increased protein concentration, whilst cloudy or turbid CSF is indicative of a markedly elevated (>100-fold) white cell concentration. The normal value of CSF protein concentration is <0.4 g L−1 . Normal CSF contains less than 10 cells L−1 ,
Fig. 2. Lumbar cerebrospinal fluid collection is particularly useful in the investigation of less common neurological conditions, such as sarcocystosis.
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predominantly lymphocytes with an occasional neutrophil. As a general rule, a predominantly polymorphonuclear intrathecal inflammatory response is found in acute bacterial infections of the central nervous system, whereas a mononuclear response is seen in viral infections. Macrophages are seen following destruction of cerebral tissue or following haemorrhage and are variably seen in polioencephalomalacia (Tvedten, 1987; Scott, 1992). Finally, there are several reports of an association between an increased CSF eosinophil concentration and parasitic infection of the central nervous system in affected sheep. Red blood cells may be present in the CSF following haemorrhage into the subarachnoid space. Pathological haemorrhage within the CSF is most confidently diagnosed by the presence of phagocytosed red blood cells within macrophages (Tvedten, 1987). A yellow discoloration of the CSF, referred to as xanthochromia, appears within a few hours after subarachnoid haemorrhage and may persist for 2–6 weeks. Haemorrhage caused by the sampling technique appears as streaking of blood in clear fluid, which may gradually disappear as more CSF is allowed to flow freely from the needle hub. Turbidity caused by recent haemorrhage into the CSF will clear after centrifugation to leave a transparent supernatant. Alternatively, if the sample is left to stand for approximately two hours, the red blood cells gravitate and form a small plug at the bottom of the collection tube. In practical terms, bacteriology results do little to further assist the clinician in the immediate diagnosis and selection of treatments and culture of lumbar CSF can be useful only in lambs with bacterial meningo-encephalitis. Neonates with bacterial meningo-encephalitis have a CSF protein concentration over 1.0 g L−1 and usually even over 2.0 g L−1 (Scott, 1993b). In that case, there is also a marked increase in CSF total while cell count in the order of 100- to 1000-fold, giving a turbid appearance and a change in the predominant white cell type from lymphocytes to almost exclusively neutrophils, commonly referred to as a neutrophilic pleiocytosis. A moderate to marked increase in CSF protein concentration in the range 0.8–4.0 g L−1 is observed in cases of meningo-encephalitis caused by Listeria monocytogenes. Mean CSF protein concentration was found to be lower for those sheep which recovered (0.9 g L−1 ) after aggressive penicillin therapy (Scott, 1993b) compared to those that were euthanased (2.2 g L−1 ). Sheep that failed to recover, had a significantly increased total leucocyte numbers, indicative of greater meningeal inflammation; neutrophils were the predominant cell type (Scott, 1993b). A large range of findings has been reported in sheep with brain abscesses. Median protein concentration was 0.6 g L−1 (range: 0.2–2.5) and median number of cells was 400 L−1 (range: 13–1300), depending upon the site of the lesion(s) and meningeal involvement (Scott, 1995). The demonstration of increased lumbar CSF protein concentration in sheep with pelvic limb and/or thoracic limb dysfunction most often indicates effusion of protein from an inflammatory lesion either impinging on the meninges or to a much lesser degree from spinal cord swelling (Scott, 1992). Both types of lesions cause disruption to the craniad
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P.R. Scott / Small Ruminant Research 110 (2013) 82–87
Fig. 3. Thoracic ultrasonography is useful in cases of suspected chronic respiratory disease of adult sheep, such as focal pleural abscesses.
Fig. 4. Confirmation of unilateral pyothorax using thoracic ultrasonography.
flow of CSF with a higher protein concentration in the caudal compartment (Scott and Will, 1991; Scott et al., 1991). Sheep with polioencephalomalacia have normal protein concentrations (Scott, 1992). There are no specific changes in CSF composition in animals with peripheral vestibular lesions.
3.1. Auscultation findings
3. Thoracic ultrasonography The presumptive clinical diagnosis of acute respiratory disease caused by Mannheimia haemolytica or Bibersteinia trehalosi (pasteurellosis) in lambs and adult sheep is based upon findings of sudden severe illness, inappetance, pyrexia, marked toxaemia and tachypnoea consistent with endotoxaemia (Donachie, 2007), but many other infectious diseases can have a similar clinical presentation, thus not permitting a definitive diagnosis. Furthermore, the response of ‘pasteurellosis’ to antibiotic and non-steroidal anti-inflammatory drug (NSAID) administration does not necessarily support the diagnosis, because many bacterial infections that present with profound endotoxaemia (Tzora et al., 2002; Jiménez et al., 2007) may also recover. Therefore, at the farm level, efforts should be directed towards prompt detection of all sick sheep (Mavrogianni and Brozos, 2008) rather than concentrate upon identifying respiratory disease. Chronic bacterial infection of the respiratory tract is altogether different and affected sheep are usually presented with weight loss over several weeks/months. Auscultation fails to identify/define specific lesions, but diagnosis can be readily achieved using ultrasonography (Scott, 2010b). Trueperella (Arcanobacterium) pyogenes is the most common bacterial isolate and such chronic infections are treated with a 4–6 weeks’ course of procaine penicillin with reasonable success. Ultrasonographic investigation of the ovine chest is not commonly used in practice and, as a consequence, many chronic ovine respiratory infections are not accurately diagnosed, hence such sheep do not receive the correct treatment (Figs. 3 and 4) (Scott, 2011).
Increased audibility of normal breath sounds over the entire lung field can reflect tachypnoea, which increases the amplitude of breath sounds by increasing the velocity of airflow in the large airways. The common causes of tachypnoea, excluding respiratory diseases, are transport and handling stresses in sheep with a full fleece during hot weather and endotoxaemia from infection of another organ system. Adventitious lung sounds are noises superimposed upon normal lung sounds (Cugell, 1987) and tend to occur consistently at the same stage of the breath cycle, over many consecutive breaths. The wide range of descriptors used in the clinical literature for abnormal (adventitious) lung sounds in sheep includes increased vesicular sounds, for a ram with severe chronic suppurative pleuropneumonia (Braun et al., 1995), and wheezing, rubbing vesicular and murmuring sounds in sheep with bacterial respiratory infections, followed by absence of residual bronchial catarrh in the same sheep during recovery (Naccari et al., 2001). However, authors in more recent papers on ovine respiratory disease (Mavrogianni and Fthenakis, 2005; Skoufos et al., 2007) have not described auscultation findings, but have referred to their distribution; no abnormal sounds recorded (score 0), abnormal sounds audible predominantly anteroventrally (score 1), abnormal sounds audible throughout the entire lung field (score 2), or, alternatively, have only commented in a more general sense on the presence of ‘loud and prolonged respiratory sounds’ (Donachie, 2007). Reference textbooks on clinical examination describe abnormal lower respiratory sounds in ruminants as clicking, popping or bubbling sounds, crackling sounds, wheezes and pleuritic friction rubs (Jackson and Cockcroft, 2002). Recent studies have highlighted the lack of correlation between lungs sounds and distribution of pathology in ‘wheel-barrow test negative’ cases of ovine pulmonary adenocarcinoma (Cousens et al., 2008). A recent publication describing adventitious lung sounds (McGorum and Dixon, 2007) presents definitions
P.R. Scott / Small Ruminant Research 110 (2013) 82–87
for wheezes and crackles as follows. Wheezes are prolonged musical sounds that occur usually during inspiration and occasionally throughout the breath cycle. They result from vibration of airway walls caused by air turbulence in narrowed airways. Wheezes are musical adventitious lung sounds, also called ‘continuous’, since their duration is much longer than that of ‘discontinuous’ crackles. Typically, they last over 80–100 ms. Two types of wheezes are recognised: monophonic wheezes, which are a single note of constant pitch, location of origin and timing within the breath cycle, and polyphonic wheezes, which comprise several different notes of different pitch and timing and represent obstruction of multiple airways. Crackles are short-duration, interrupted, non-musical sounds. Two types of crackles may be recognised. Coarse crackles are loud, explosive, of short duration (typically 10–30 ms), non-musical, ‘rattling or bubbling’ sounds. Coarse crackles are possibly caused by air bubbling through, and causing vibrations of, respiratory secretions within the larger intrathoracic airways, including those that are pooling within the dependent part of the rostral thoracic trachea. Fine crackles are of shorter duration (typically 1–10 ms), lower amplitude and have a higher pitch. Routine interpretation of auscultated sounds did not allow the presence of superficial lung pathology or its distribution to be accurately defined in the respiratory diseases represented in a recent study (Scott et al., 2010). Focal pleural abscesses could not be detected on auscultation alone, which may explain why there are no clinical descriptions of this condition in textbooks on ovine respiratory disease. Attenuation of lung sounds was recorded in cases of pleural effusion, pyothorax and extensive fibrinous pleurisy (Scott et al., 2010). No sounds resembling the description of pleural friction rubs were heard in cases of marked fibrinous pleurisy or associated with pleural abscesses. Moderate to severe coarse crackles detected in advanced ovine pulmonary adenocarcinoma cases were audible over a larger area than lesion distribution identified during ultrasound examination. 3.2. Ultrasonographic examination of the thorax Ultrasonographic examination of the ovine chest is inexpensive, non-invasive and, unlike radiography, has no special health and safety procedures or restrictions (Scott, 2008). An air interface, created by normal aerated lung parenchyma reflects sound waves and appears as a bright white (hyperechoic) linear echo (Scott and Gessert, 1998). Superficial areas of consolidated lung parenchyma or fluid within an abscess transmit sound waves and appear more hypoechoic than surrounding lung tissue. Pleural fluid transmits sound waves readily and appears as an anechoic (black) area. Gas-filled pockets within pleural fluid or abscess capsule appear as bright hyperechoic spots within the anechoic area (‘snowstorm appearance’). Ultrasonographic examination of fibrinous pleurisy reveals separation of the pleurae and lung lobes by a hypoechoic area with acoustic enhancement of the visceral pleura. In more severe cases’ the fibrin deposits have a hyperechoic latticework appearance containing hypoechoic areas extending for up to 8–10 cm. Pleural abscesses appear
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Fig. 5. Chronic bacterial infection of the elbow joint, leading to destruction of the articular surfaces and loss of the joint space; in this case, radiography can add little to the diagnostic plan.
as uniform hypoechoic areas extending containing many hyperechoic spots and extend up to 16 cm deep, involving one side of the chest containing up to 2–3 l of purulent material (pyothorax). Lung abscesses are common in adult sheep, especially rams, but are difficult to diagnose by clinical examination alone (Scott, 2007). Affected sheep present with chronic weight loss over several weeks to months and are often dull, although appetite may appear normal. The rectal temperature is only slightly elevated (up to 40.0 ◦ C). At rest, affected sheep are tachypnoeic, cough occasionally and there may be a scant mucopurulent nasal discharge. T. pyogenes is a common isolate from lung abscesses (Barbour et al., 1997), where penicillin is the antibiotic of choice (Scott and Gessert, 1998; Scott, 2007; Scott et al., 2010). 4. Arthrocentesis and radiography of joint lesions Diagnosis of a septic joint in adult sheep is based upon findings of severe lameness (defined as intense and of long duration), with thickening of the joint capsule due to delays between infection and presentation. There is usually no significant joint effusion and most joints contain only small amounts of fibrin/pannus. A pannus is defined as a membrane of granulation tissue (fibroblasts and neo-vascularisation) and bone marrowderived cells (macrophages). Formation of the pannus stimulates the release of IL-1, platelet-derived growth factor, prostaglandins and substance P by macrophages and release of collagenases by fibroblasts, which ultimately cause cartilage destruction and bone erosion encountered in neglected sheep. Osteophyte formation occurs initially at the insertion of the joint capsule, because that area has the greatest blood supply. Neo-vascularisation that occurs within the pannus, stimulates new bone formation, which may progress to ankylosis, if the lameness is ignored and the pathological process allowed to continue. Samples collected from chronically affected ovine joints frequently fail to yield bacteria. Direct smears of the aspirate can be made onto a glass slide and stained with Gram stain or DiffQuik, in order to gain some information of
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P.R. Scott / Small Ruminant Research 110 (2013) 82–87
Conflict of interest statement The author knows of no conflict of interest in the preparation of this manuscript.
References
Fig. 6. Joint infection of the elbow joint revealing only slight widening of the joint space. Radiography of acute joint infections in small ruminants can prove misleading and should be interpreted with caution.
the potential pathogen(s) involved. Smears of the synovial membrane at necropsy may yield better results. Radiography adds little additional information, except to reveal infections acquired via the growth plate and neglected cases, where sheep had been lame for over 3 months with considerable osteophyte formation (Fig. 5). A field study of 39 sheep older than 9 months reported that radiography provided useful information in only five sheep with growth plate infections and in the four sheep with a suspected hip infection (Scott and Sargison, 2012). There was no obvious disruption of the joint space (widening due to accumulation of inflammatory exudate) in cases with a septic joint of less than 1 week’s duration (Fig. 6). There was a poor response to joint lavage under general anaesthesia in this study with only one of four sheep affected for less than five days becoming sound (Scott and Sargison, 2012).
5. Concluding remarks Lumbar cerebrospinal fluid analysis is indicated for those samples collected from small ruminants with evidence of a spinal cord lesion and those animals which are presented with uncommon clinical signs, where there is no conclusive diagnosis based upon the neurological examination alone. Thoracic ultrasonography should be used in cases of suspected chronic respiratory disease of adult sheep and is most useful in the diagnosis of pleural abscess and early lesion of ovine pulmonary adenocarcinoma, which are not detected during auscultation of the chest. Radiography of acute joint infections in small ruminants can prove misleading and should be interpreted with caution; osteophyte formation associated with chronic joint infections may not be detectable on radiographic examination, until at least 3 months after joint infection, therefore this ancillary aid has little clinical application for investigation joint infections in clinical practice.
Barbour, E.K., Nabbut, N.H., Hamadeh, S.K., Al-Nakhli, H.M., 1997. Bacterial identity and characteristics in healthy and unhealthy respiratory tracts of sheep and calves. Vet. Res. Commun. 21, 421–430. Braun, U., Flukiger, M., Sicher, D., Theil, D., 1995. Suppurative pleuropneumonia and apulmonary abscess in a ram: ultrasonographic and radiographic findings. Schweiz. Archiv. Tierh. 137, 272–278. Cousens, C., Graham, M., Sales, J., Dagleish, M.P., 2008. Evaluation of the efficacy of clinical diagnosis of ovine pulmonary adenocarcinoma. Vet. Rec. 162, 88–90. Cugell, D.W., 1987. Lung sound nomenclature. American Review of Respiratory Disease 136, 1016. Donachie, W., 2007. Pasteurellosis. In: Aitken, I.D. (Ed.), Diseases of Sheep. Blackwell, Oxford, UK, pp. 224–235. Jackson, P.G.G., Cockcroft, P.D.,2002. Clinical examination of the respiratory system. In: Clinical Examination of Farm Animals. Blackwell, Oxford, UK, pp. 65–80. Jiménez, A., Sánchez, J., Andrés, S., Alonso, J.M., Gómez, L., López, F., Rey, J., 2007. Evaluation of endotoxaemia in the prognosis and treatment of scouring Merino lambs. J. Vet. Med. A 54, 103–106. Mavrogianni, V.S., Brozos, C., 2008. Reflections on the causes and the diagnosis of peri-parturient losses of ewes. Small Rumin. Res. 76, 77–82. Mavrogianni, V.S., Fthenakis, G.C., 2005. Efficacy of difloxacin against respiratory infections of lambs. J. Vet. Pharmacol. Therap. 28, 325–328. McGorum, B.C., Dixon, P.M., 2007. Clinical examination of the respiratory tract. In: McGorum, B.C., Dixon, P.M., Robinson, N.E., Schumacher, J. (Eds.), Equine respiratory medicine and surgery. Saunders, London, UK, pp. 103–119. Naccari, F., Giofrè, F., Pellegrino, M., Calò, M., Licata, P., Carli, S., 2001. Effectiveness and kinetic behaviour of tilmicosin in the treatment of respiratory infections in sheep. Vet. Rec. 148, 773–776. Scott, P.R., 1992. Cerebrospinal fluid collection and analysis in some common ovine neurological conditions. Br. Vet. J. 148, 15–22. Scott, P.R., 1993a. Cerebrospinal fluid collection in ruminant neurological disease. In Practice 15, 298–300. Scott, P.R., 1993b. A field study of ovine listerial meningo-encephalitis with particular reference to cerebrospinal fluid analysis as an aid to diagnosis and prognosis. Br. Vet. J. 149, 165–170. Scott, P.R., 1994. Practical application of cerebrospinal fluid analysis in the differential diagnosis of spinal cord lesions in ruminants. In Practice 16, 301–303. Scott, P.R., 1995. The collection and analysis of cerebrospinal fluid as an aid to diagnosis in ruminant neurological disease. Br. Vet. J. 151, 603–614. Scott, P.R., 2004. Diagnostic techniques and clinicopathological findings in ruminant neurological disease. Vet. Clin. N. Am. Food Anim. Pract. 20, 215–230. Scott, P.R., 2007. Sheep Medicine. Manson, London, UK, pp. 336. Scott, P.R., 2008. The role of ultrasonography as an adjunct to clinical examination in sheep practice. Irish Vet. J. 61, 474–480. Scott, P.R., 2010a. Cerebrospinal fluid collection and analysis in suspected sheep neurological disease. Small Rumin. Res. 92, 96–103. Scott, P.R., 2010b. Lung auscultation recordings from normal sheep and from sheep with well-defined respiratory tract pathology. Small Rumin. Res. 92, 104–107. Scott, P.R., 2011. Treatment and control of respiratory disease in sheep. Vet. Clin. N. Am. Food Anim. Pract. 27, 175–186. Scott, P.R., Collie, D.D.S., McGorum, B.C., Sargison, N.D., 2010. Relationship between thoracic auscultation and lung pathology detected by ultrasonography in sheep. Vet. J. 186, 53–57. Scott, P.R., Gessert, M.E., 1998. Ultrasonographic examination of the ovine thorax. Vet. J. 155, 305–310. Scott, P.R., Murray, L.M., Penny, C.D., 1991. A field study of eight ovine vertebral body abscess cases. N. Z. Vet. J. 39, 105–107. Scott, P.R., Sargison, N.D., 2012. Diagnosis and treatment of joint infections in 39 adult sheep. Small Rumin. Res. 106, 16–20. Scott, P.R., Will, R.G., 1991. Froin’s syndrome in five cases of ovine epidural abscess. Br. Vet. J. 147, 582–584.
P.R. Scott / Small Ruminant Research 110 (2013) 82–87 Skoufos, J., Christodoulopoulos, G., Fragkou, I.A., Tzora, A., Gougoulis, D.A., Orfanou, D.C., Tsiolaki, K., Fthenakis, G.C., 2007. Efficacy of marbofloxacin against respiratory infections of lambs. Small Rumin. Res. 71, 304–309. Tvedten, H.W., 1987. Clinical pathology of bovine neurologic disease. Vet. Clin. N. Am. Food Anim. Pract. 3, 25–44.
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Tzora, A., Leontides, L.S., Amiridis, G.S., Manos, G., Fthenakis, G.C., 2002. Bacteriological and epidemiological findings during examination of the uterine content of ewes with retention of fetal membranes. Theriogenology 57, 1809–1817.
Contents lists available at SciVerse ScienceDirect
Small Ruminant Research journal homepage: www.elsevier.com/locate/smallrumres
Analysis of samples of cerebrospinal fluid, thoracic ultrasonography and arthrocentesis/radiography of joints as ancillary aids to clinical diagnosis and treatment in small ruminant practice夽 P.R. Scott University of Edinburgh, Royal (Dick) School of Veterinary Studies, Easter Bush Veterinary Centre, Roslin, Midlothian, United Kingdom
a r t i c l e
i n f o
Article history: Available online 11 December 2012 Keywords: Arthritis Cerebrospinal fluid Radiography Respiratory disease Sheep Ultrasonography
a b s t r a c t Two useful ancillary tests for the busy small ruminant practitioner are analysis of samples of lumbar cerebrospinal fluid, collected from unusual and/or problematic cases, and thoracic ultrasonography in suspected chronic respiratory disease of adult sheep. In contrast, arthrocentesis and radiography of joint lesions in adult sheep can prove misleading and should be interpreted with caution. © 2012 Elsevier B.V. All rights reserved.
1. Introduction There is a wide range of ancillary aids that can be employed by the small ruminant practitioner, to help confirm the provisional diagnosis reached during the clinical examination. This article reviews those clinical presentations, where analysis of samples of cerebrospinal fluid, thoracic ultrasonography and arthrocentesis/radiography of joints may prove useful in clinical practice. 2. Collection and analysis of cerebrospinal fluid samples Collection and analysis of lumbar cerebrospinal fluid samples is particularly useful to confirm the presence of an inflammatory lesion involving the leptomeninges, such as bacterial meningo-encephalitis, and to investigate potential compressive lesions of the spinal cord (Fig. 1) and less
夽 This paper is part of the special issue entitled “Lectures of the 1st European Conference on Small Ruminant Health Management”, held in Athens, Greece, October 2011. Guest Edited by G.C. Fthenakis. E-mail address: [email protected] 0921-4488/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.smallrumres.2012.11.009
common neurological conditions (e.g., sarcocystosis; Fig. 2) (Scott, 1992, 2004, 2010a). 2.1. Method for sample collection Collection of lumbar cerebrospinal fluid (CSF) is facilitated when the sheep is positioned in sternal recumbency, with the hips flexed and the pelvic limbs extended alongside the abdomen. The sheep’s head is averted against the animal’s flank (Scott, 1993a, 1994). Sedation of the animal is not usually necessary, but intramuscular xylazine (0.05 mg kg−1 bodyweight) or diazepam (0.04 mg kg−1 bodyweight) can be used to aid restraint and facilitate positioning of the animal. The site for lumbar CSF collection is the midpoint of the lumbosacral space identified as the midline depression between the last palpable dorsal lumbar spine (L6) and the first palpable sacral dorsal spine (S2). This site is approximately 1–2 cm caudal to an imaginary line joining the wings of the ilium. The needle is slowly advanced over 10 s at a right angle to the plane of the vertebral column or with the hub directed 5–10◦ caudally. It is essential to appreciate the changes in tissue resistance as the needle
P.R. Scott / Small Ruminant Research 110 (2013) 82–87
Fig. 1. Lumbar cerebrospinal fluid collection is particularly useful in the investigation of compressive lesions of the spinal cord.
point passes sequentially through the subcutaneous tissue, interarcuate ligament then the sudden ‘pop’, due to the loss of resistance as the needle point exits the ligamentum flavum into the extradural space. Once the needle has been advanced fractionally further and its point has penetrated the dorsal subarachnoid space, CSF will well up in the needle hub within 2–3 s. A CSF quantity of 1–2 mL is sufficient for laboratory analysis and, although the sample can be collected by free flow over 1–2 min, it is more convenient to employ very gentle syringe aspiration over 20 s. There is no justification to collect from the ventral subarachnoid space. 2.2. Analysis Cerebrospinal fluid is clear and colourless. It is noteworthy that agitation of the sample will cause damage to cell morphology. Stable foam is indicative of increased protein concentration, whilst cloudy or turbid CSF is indicative of a markedly elevated (>100-fold) white cell concentration. The normal value of CSF protein concentration is <0.4 g L−1 . Normal CSF contains less than 10 cells L−1 ,
Fig. 2. Lumbar cerebrospinal fluid collection is particularly useful in the investigation of less common neurological conditions, such as sarcocystosis.
83
predominantly lymphocytes with an occasional neutrophil. As a general rule, a predominantly polymorphonuclear intrathecal inflammatory response is found in acute bacterial infections of the central nervous system, whereas a mononuclear response is seen in viral infections. Macrophages are seen following destruction of cerebral tissue or following haemorrhage and are variably seen in polioencephalomalacia (Tvedten, 1987; Scott, 1992). Finally, there are several reports of an association between an increased CSF eosinophil concentration and parasitic infection of the central nervous system in affected sheep. Red blood cells may be present in the CSF following haemorrhage into the subarachnoid space. Pathological haemorrhage within the CSF is most confidently diagnosed by the presence of phagocytosed red blood cells within macrophages (Tvedten, 1987). A yellow discoloration of the CSF, referred to as xanthochromia, appears within a few hours after subarachnoid haemorrhage and may persist for 2–6 weeks. Haemorrhage caused by the sampling technique appears as streaking of blood in clear fluid, which may gradually disappear as more CSF is allowed to flow freely from the needle hub. Turbidity caused by recent haemorrhage into the CSF will clear after centrifugation to leave a transparent supernatant. Alternatively, if the sample is left to stand for approximately two hours, the red blood cells gravitate and form a small plug at the bottom of the collection tube. In practical terms, bacteriology results do little to further assist the clinician in the immediate diagnosis and selection of treatments and culture of lumbar CSF can be useful only in lambs with bacterial meningo-encephalitis. Neonates with bacterial meningo-encephalitis have a CSF protein concentration over 1.0 g L−1 and usually even over 2.0 g L−1 (Scott, 1993b). In that case, there is also a marked increase in CSF total while cell count in the order of 100- to 1000-fold, giving a turbid appearance and a change in the predominant white cell type from lymphocytes to almost exclusively neutrophils, commonly referred to as a neutrophilic pleiocytosis. A moderate to marked increase in CSF protein concentration in the range 0.8–4.0 g L−1 is observed in cases of meningo-encephalitis caused by Listeria monocytogenes. Mean CSF protein concentration was found to be lower for those sheep which recovered (0.9 g L−1 ) after aggressive penicillin therapy (Scott, 1993b) compared to those that were euthanased (2.2 g L−1 ). Sheep that failed to recover, had a significantly increased total leucocyte numbers, indicative of greater meningeal inflammation; neutrophils were the predominant cell type (Scott, 1993b). A large range of findings has been reported in sheep with brain abscesses. Median protein concentration was 0.6 g L−1 (range: 0.2–2.5) and median number of cells was 400 L−1 (range: 13–1300), depending upon the site of the lesion(s) and meningeal involvement (Scott, 1995). The demonstration of increased lumbar CSF protein concentration in sheep with pelvic limb and/or thoracic limb dysfunction most often indicates effusion of protein from an inflammatory lesion either impinging on the meninges or to a much lesser degree from spinal cord swelling (Scott, 1992). Both types of lesions cause disruption to the craniad
84
P.R. Scott / Small Ruminant Research 110 (2013) 82–87
Fig. 3. Thoracic ultrasonography is useful in cases of suspected chronic respiratory disease of adult sheep, such as focal pleural abscesses.
Fig. 4. Confirmation of unilateral pyothorax using thoracic ultrasonography.
flow of CSF with a higher protein concentration in the caudal compartment (Scott and Will, 1991; Scott et al., 1991). Sheep with polioencephalomalacia have normal protein concentrations (Scott, 1992). There are no specific changes in CSF composition in animals with peripheral vestibular lesions.
3.1. Auscultation findings
3. Thoracic ultrasonography The presumptive clinical diagnosis of acute respiratory disease caused by Mannheimia haemolytica or Bibersteinia trehalosi (pasteurellosis) in lambs and adult sheep is based upon findings of sudden severe illness, inappetance, pyrexia, marked toxaemia and tachypnoea consistent with endotoxaemia (Donachie, 2007), but many other infectious diseases can have a similar clinical presentation, thus not permitting a definitive diagnosis. Furthermore, the response of ‘pasteurellosis’ to antibiotic and non-steroidal anti-inflammatory drug (NSAID) administration does not necessarily support the diagnosis, because many bacterial infections that present with profound endotoxaemia (Tzora et al., 2002; Jiménez et al., 2007) may also recover. Therefore, at the farm level, efforts should be directed towards prompt detection of all sick sheep (Mavrogianni and Brozos, 2008) rather than concentrate upon identifying respiratory disease. Chronic bacterial infection of the respiratory tract is altogether different and affected sheep are usually presented with weight loss over several weeks/months. Auscultation fails to identify/define specific lesions, but diagnosis can be readily achieved using ultrasonography (Scott, 2010b). Trueperella (Arcanobacterium) pyogenes is the most common bacterial isolate and such chronic infections are treated with a 4–6 weeks’ course of procaine penicillin with reasonable success. Ultrasonographic investigation of the ovine chest is not commonly used in practice and, as a consequence, many chronic ovine respiratory infections are not accurately diagnosed, hence such sheep do not receive the correct treatment (Figs. 3 and 4) (Scott, 2011).
Increased audibility of normal breath sounds over the entire lung field can reflect tachypnoea, which increases the amplitude of breath sounds by increasing the velocity of airflow in the large airways. The common causes of tachypnoea, excluding respiratory diseases, are transport and handling stresses in sheep with a full fleece during hot weather and endotoxaemia from infection of another organ system. Adventitious lung sounds are noises superimposed upon normal lung sounds (Cugell, 1987) and tend to occur consistently at the same stage of the breath cycle, over many consecutive breaths. The wide range of descriptors used in the clinical literature for abnormal (adventitious) lung sounds in sheep includes increased vesicular sounds, for a ram with severe chronic suppurative pleuropneumonia (Braun et al., 1995), and wheezing, rubbing vesicular and murmuring sounds in sheep with bacterial respiratory infections, followed by absence of residual bronchial catarrh in the same sheep during recovery (Naccari et al., 2001). However, authors in more recent papers on ovine respiratory disease (Mavrogianni and Fthenakis, 2005; Skoufos et al., 2007) have not described auscultation findings, but have referred to their distribution; no abnormal sounds recorded (score 0), abnormal sounds audible predominantly anteroventrally (score 1), abnormal sounds audible throughout the entire lung field (score 2), or, alternatively, have only commented in a more general sense on the presence of ‘loud and prolonged respiratory sounds’ (Donachie, 2007). Reference textbooks on clinical examination describe abnormal lower respiratory sounds in ruminants as clicking, popping or bubbling sounds, crackling sounds, wheezes and pleuritic friction rubs (Jackson and Cockcroft, 2002). Recent studies have highlighted the lack of correlation between lungs sounds and distribution of pathology in ‘wheel-barrow test negative’ cases of ovine pulmonary adenocarcinoma (Cousens et al., 2008). A recent publication describing adventitious lung sounds (McGorum and Dixon, 2007) presents definitions
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for wheezes and crackles as follows. Wheezes are prolonged musical sounds that occur usually during inspiration and occasionally throughout the breath cycle. They result from vibration of airway walls caused by air turbulence in narrowed airways. Wheezes are musical adventitious lung sounds, also called ‘continuous’, since their duration is much longer than that of ‘discontinuous’ crackles. Typically, they last over 80–100 ms. Two types of wheezes are recognised: monophonic wheezes, which are a single note of constant pitch, location of origin and timing within the breath cycle, and polyphonic wheezes, which comprise several different notes of different pitch and timing and represent obstruction of multiple airways. Crackles are short-duration, interrupted, non-musical sounds. Two types of crackles may be recognised. Coarse crackles are loud, explosive, of short duration (typically 10–30 ms), non-musical, ‘rattling or bubbling’ sounds. Coarse crackles are possibly caused by air bubbling through, and causing vibrations of, respiratory secretions within the larger intrathoracic airways, including those that are pooling within the dependent part of the rostral thoracic trachea. Fine crackles are of shorter duration (typically 1–10 ms), lower amplitude and have a higher pitch. Routine interpretation of auscultated sounds did not allow the presence of superficial lung pathology or its distribution to be accurately defined in the respiratory diseases represented in a recent study (Scott et al., 2010). Focal pleural abscesses could not be detected on auscultation alone, which may explain why there are no clinical descriptions of this condition in textbooks on ovine respiratory disease. Attenuation of lung sounds was recorded in cases of pleural effusion, pyothorax and extensive fibrinous pleurisy (Scott et al., 2010). No sounds resembling the description of pleural friction rubs were heard in cases of marked fibrinous pleurisy or associated with pleural abscesses. Moderate to severe coarse crackles detected in advanced ovine pulmonary adenocarcinoma cases were audible over a larger area than lesion distribution identified during ultrasound examination. 3.2. Ultrasonographic examination of the thorax Ultrasonographic examination of the ovine chest is inexpensive, non-invasive and, unlike radiography, has no special health and safety procedures or restrictions (Scott, 2008). An air interface, created by normal aerated lung parenchyma reflects sound waves and appears as a bright white (hyperechoic) linear echo (Scott and Gessert, 1998). Superficial areas of consolidated lung parenchyma or fluid within an abscess transmit sound waves and appear more hypoechoic than surrounding lung tissue. Pleural fluid transmits sound waves readily and appears as an anechoic (black) area. Gas-filled pockets within pleural fluid or abscess capsule appear as bright hyperechoic spots within the anechoic area (‘snowstorm appearance’). Ultrasonographic examination of fibrinous pleurisy reveals separation of the pleurae and lung lobes by a hypoechoic area with acoustic enhancement of the visceral pleura. In more severe cases’ the fibrin deposits have a hyperechoic latticework appearance containing hypoechoic areas extending for up to 8–10 cm. Pleural abscesses appear
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Fig. 5. Chronic bacterial infection of the elbow joint, leading to destruction of the articular surfaces and loss of the joint space; in this case, radiography can add little to the diagnostic plan.
as uniform hypoechoic areas extending containing many hyperechoic spots and extend up to 16 cm deep, involving one side of the chest containing up to 2–3 l of purulent material (pyothorax). Lung abscesses are common in adult sheep, especially rams, but are difficult to diagnose by clinical examination alone (Scott, 2007). Affected sheep present with chronic weight loss over several weeks to months and are often dull, although appetite may appear normal. The rectal temperature is only slightly elevated (up to 40.0 ◦ C). At rest, affected sheep are tachypnoeic, cough occasionally and there may be a scant mucopurulent nasal discharge. T. pyogenes is a common isolate from lung abscesses (Barbour et al., 1997), where penicillin is the antibiotic of choice (Scott and Gessert, 1998; Scott, 2007; Scott et al., 2010). 4. Arthrocentesis and radiography of joint lesions Diagnosis of a septic joint in adult sheep is based upon findings of severe lameness (defined as intense and of long duration), with thickening of the joint capsule due to delays between infection and presentation. There is usually no significant joint effusion and most joints contain only small amounts of fibrin/pannus. A pannus is defined as a membrane of granulation tissue (fibroblasts and neo-vascularisation) and bone marrowderived cells (macrophages). Formation of the pannus stimulates the release of IL-1, platelet-derived growth factor, prostaglandins and substance P by macrophages and release of collagenases by fibroblasts, which ultimately cause cartilage destruction and bone erosion encountered in neglected sheep. Osteophyte formation occurs initially at the insertion of the joint capsule, because that area has the greatest blood supply. Neo-vascularisation that occurs within the pannus, stimulates new bone formation, which may progress to ankylosis, if the lameness is ignored and the pathological process allowed to continue. Samples collected from chronically affected ovine joints frequently fail to yield bacteria. Direct smears of the aspirate can be made onto a glass slide and stained with Gram stain or DiffQuik, in order to gain some information of
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Conflict of interest statement The author knows of no conflict of interest in the preparation of this manuscript.
References
Fig. 6. Joint infection of the elbow joint revealing only slight widening of the joint space. Radiography of acute joint infections in small ruminants can prove misleading and should be interpreted with caution.
the potential pathogen(s) involved. Smears of the synovial membrane at necropsy may yield better results. Radiography adds little additional information, except to reveal infections acquired via the growth plate and neglected cases, where sheep had been lame for over 3 months with considerable osteophyte formation (Fig. 5). A field study of 39 sheep older than 9 months reported that radiography provided useful information in only five sheep with growth plate infections and in the four sheep with a suspected hip infection (Scott and Sargison, 2012). There was no obvious disruption of the joint space (widening due to accumulation of inflammatory exudate) in cases with a septic joint of less than 1 week’s duration (Fig. 6). There was a poor response to joint lavage under general anaesthesia in this study with only one of four sheep affected for less than five days becoming sound (Scott and Sargison, 2012).
5. Concluding remarks Lumbar cerebrospinal fluid analysis is indicated for those samples collected from small ruminants with evidence of a spinal cord lesion and those animals which are presented with uncommon clinical signs, where there is no conclusive diagnosis based upon the neurological examination alone. Thoracic ultrasonography should be used in cases of suspected chronic respiratory disease of adult sheep and is most useful in the diagnosis of pleural abscess and early lesion of ovine pulmonary adenocarcinoma, which are not detected during auscultation of the chest. Radiography of acute joint infections in small ruminants can prove misleading and should be interpreted with caution; osteophyte formation associated with chronic joint infections may not be detectable on radiographic examination, until at least 3 months after joint infection, therefore this ancillary aid has little clinical application for investigation joint infections in clinical practice.
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