EQUINE CLINICAL PATHOLOGY - Rossdale & Partners

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T h e B e a u f o r t c o t t a g e l a b o r a t o r i e s Synovial fluid Analysis of Synovial Fluid is useful for the diagnosis of reactive or septic arthritis in horses after injury, when a joint becomes distended, with or without lameness, and to differentiate septic ('joint-ill') from traumatic arthritis in foals. To perform a joint tap, septic techniques for needle puncture should be used. The joint to be sampled and its anatomical relationships govern the site of puncture and to a degree the techniques used. Total nucleated cell counts 10 x 10 9 /l, with degenerative and toxic cytopathological changes. Tracheal washes or aspirations These samples can be extremely useful in confirming and characterising airway inflammation (leucocytes) in cases of septic tracheobronchitis and in reactive and obstructive small airway disease. Samples can be collected via a suitablelength sterile endoscope. The endoscope is passed through the pharynx, larynx and into the trachea. A long sterile polyethylene tube is passed down the instrument channel and accumulated secretions may be aspirated directly. Alternatively, and more usually, 50 ml sterile saline may be injected as quickly as possible and then aspirated while withdrawing the tube. If a suitable endoscope is not available, a sterile polyethylene tube may be passed down a trochar inserted surgically between two tracheal rings at the mid lower third of the cervical trachea. This is clearly a more invasive technique that may lead to local wound complications but has the advantage that there is less likelihood of contamination of the sample with commensal bacteria from the oropharynx. Trans-tracheal aspirates, collected by this method, are particularly useful in cases of pleuropneumonia where causative organisms must be specifically identified to direct antimicrobial therapy. Bronchoalveolar lavage (BAL) samples BAL samples can be helpful in the diagnosis of small airway disease. One must remember that the technique samples a focal area only and does not help with the diagnosis of tracheobronchitis. It is therefore more commonly used in older horses for the characterisation of reactive airway obstruction. Cytological examinations of tracheal wash or BAL samples may help in the characterisation of mucous production and acute and chronic, septic and reactive (non-septic) inflammatory responses. The demonstration of significant numbers of eosinophils in association with signs of septic bronchitis/bronchiolitis may be a useful 44
G u i d e t o e q u i n e c l i n i c a l p a t h o l o g y diagnostic aid for lungworm (Dictyocaulus arnfieldi) infestation, in horses and ponies coughing at pasture. Bacterial culture can be useful in identifying specific pathogens and guiding antimicrobial therapy. Cerebrospinal (CSF) samples CSF samples are most commonly collected in horses showing neurological signs for the diagnosis and differentiation of meningitis or traumatic injury. In horses imported from countries where equine protozoal myeloencephalitis occurs and who develop neurological signs, CSF analysis is indicated. For a CSF tap, samples are collected from the atlanto-occipital space with the horse restrained in lateral recumbency with the poll flexed. In foals it may be possible to perform this under heavy sedation whereas in adults, general anaesthesia is mandatory. The skin is clipped and prepared as if for surgical intervention and a bleb of local anaesthetic is placed in the midline of the dorsal neck at a level defined by a line joining the cranial borders or the atlas, which may be clearly palpated. A sterile 18 gauge 2 inch needle is then inserted through the skin at 90° and advanced until it ‘pops’ through the meninges and CSF drips or pours from the needle into a sterile container or is aspirated into a sterile syringe. Alternatively, in adult horses, CSF may be collected via the lumbosacral (LS) space, by lumbosacral tap. The horse is restrained, sedated, in stocks. The skin between the tuber coxae is clipped and prepared as if for surgical intervention. A sizeable (3-4 ml) bleb of local anaesthetic is placed in and under the skin in the midline at a line bisecting the caudal borders of the tuber coxae. With the horse standing ’square’ with weight evenly distributed on both hind legs, a sterile 18 gauge 6 inch spinal needle with stylette in place is then inserted though the skin in the midline at the line bisecting the tuber coxae and down through the palpable depression just caudal to the sixth lumbar spinous process. The horse will often flinch when the subarachnoid space is penetrated and this is an indication to start aspiration into a sterile syringe for a fluid sample. Gross examination of CSF reveals a clear almost colourless fluid in normality and a turbid and/or bloodstained fluid with meningitis or following traumatic injury. Laboratory examinations of CSF need to be able to measure very low total nucleated cell counts (
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EQUINE CLINICAL PATHOLOGY - Rossdale & Partners

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