|Sample Requirement||Turnaround Time|
EDTA, plain, cytospin
+/- swab for culture
Same working day (cytology)
~48 hours (culture)
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. The sample should be submitted to the laboratory in a plain tube for cell count and biochemistry, and diluted 50:50 with cytopreservative solution (available on request) for cytology.
Routine examination includes white cell count (counting chamber method due to low cell counts, expected range 0-6 x 106/l), total protein (microprotein method, expected range 0-1g/l), creatine kinase, sodium, potassium and chloride, cytology. In horses that are from endemic areas that are suspected of protozoal myeloencephalitis, we can refer CSF samples to specialist laboratories for serological and DNA (PCR) testing. Cytocentrifuge prepared smears are essential to provide adequate numbers of cells for meaningful cytopathological appraisal.