South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
response to treatments.Unfortunately, variation within and between observers makes this
subjective analysis of gait more problematic (Olsen et al. 2014).
The following neurological disorders should be considered potential differential diagnoses and
may produce signs similar to or indistinguishable from CSM: equine protozoal myeloencephalitis
(EPM), equine degenerative myeloencephalopathy (EDM), equine herpes virus I myelitis,
occipito-atlantoaxial malformation, spinal cord trauma, vertebral fracture, vertebral abscess or
neoplasia, and verminous myelitis.
Horses with traumatic cervical vertebral disorders usually exhibit pain during manipulation or
palpation of the neck, and the disorder may sometimes be differentiated from CSM by standing
radiographic examination. Occipito-atlantoaxial malformation occurs primarily in Arabian horses
and is diagnosed definitively by radiographic examination. Equine degenerative
myeloencephalopathy is diagnosed by exclusion (unremarkable cerebrospinal fluid cytological
examination, negative immunoblot analysis for Sarcocystis neurona, and negative radiographic
and myelographic examination). The veterinarian may suspect EDM based on the age (usually
less than 18 months) and during neurological examination but definitive diagnosis is only
achieved by post-mortem examination. Although several breeds have been reported with the
disease, EDM appears to have a familial predisposition in Standardbred horses. Horses with
equine herpes virus I myelitis may have urinary incontinence, poor tail tone and pelvic limb lower
motor neuron weakness. Signs associated with cranial nerve involvement may occasionally be
observed. In EHV1 myelitis, CSF evaluation typically reveals xanthochromia and
albuminocytological dissociation (high protein, normal cell count); a rising or already markedly
elevated EHV1 serum antibody titre, virus isolation and PCR diagnosis all can be used to provide
supportive evidence of herpes virus I myelitis. In areas where EPM is endemic (such as North and
South America) or in horses imported from these regions, distinguishing between EPM and CSM
can be hard. Asymmetrical signs such as focal sweating and regional muscle atrophy should direct
diagnostic efforts toward EPM, however symmetrical spinal ataxia does not preclude a diagnosis
of EPM. EPM-affected horses with symmetrical ataxia are differentiated from those with CSM on
the basis of standing radiographic evaluation, CSF immune-diagnostic analysis for S. neurona,
and in some circumstances, myelographic evaluation (see comments on equine myelography
below). Cytological analysis of CSF is usually unremarkable in horses with CSM, although mild
xanthochromia or slightly increased protein concentration can be observed in affected horses
especially if signs have developed acutely, perhaps precipitated by trauma.
Diagnostic testing
Plain radiography of the cervical vertebrae can be used to assess the likelihood of cervical stenotic
myelopathy in horses with spinal ataxia (Moore et al. 1994), but accurate assessment requires a
precise lateral radiograph, (Rush 1998) ensuring that the ventral prominences of the transverse
processes are perfectly overlying each other. Radiographic obliquity results in indistinct margins
of the ventral aspect of the vertebral canal, and results in erroneous values for objective
measurements. A thorough understanding of the 3 dimensional anatomy of the cervical vertebrae
aids in interpretation (Withers et al. 2009). Cervical radiographs should be evaluated subjectively
and objectively. Subjective interpretation is based on examining for presence of five characteristic
malformations of the cervical vertebrae that include (1) flare of the caudal epiphysis of the
vertebral body; (2) abnormal ossification of the articular processes; (3) subluxation /
misalignment between adjacent vertebrae; (4) extension of the vertebral caudal dorsal lamina and
(5) osteoarthritis of the articular processes. Estimating the significance of lesions identified
through subjective interpretation can be hard and is based on the clinician‟s experience and
interpreting the balance of probability. For example, osteoarthritis of (especially the caudal)
vertebral articular processes is recognised commonly in normal horses (Whitwell and Dyson
1987). Hence recognition of characteristic vertebral malformations is considered supportive in
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