Differential diagnoses for spinal ataxia in horses includes: cervical vertebral stenotic myelopathy (CVSM), equine protozoal
myelitis (EPM), trauma, congenital abnormalities, equine degenerative myelopathy (EDM), and equine herpes virus-1. This lecture
will present each differential by a case by case basis, and then summarize.
Cervical vertebral stenotic myelopathy:
Signalment: two age groups.
Young horses: Have spinal cord compression as a result of developmental abnormalities of the cervical vertebral column. Young
horses are usually well feed and fast growing. Typical age at presentation is 1-2 years (but maybe older or younger).
Older horses: May present with ataxia or predominately neck pain due to osteoarthritis of the articular facets of the vertebrae.
Young horses: Onset of ataxia maybe insidious or more acute. Symmetric ataxia, paresis, dysmetria and spasticity in all 4
limbs. Hindlimbs usually 1 grade worse than front. No cranial nerve signs. Usually no significant neck pain.
Older horses: Usually ataxia is symmetric (with hindlimbs more severely affected). In some horses may notice asymmetry of
ataxia due to lateral compression of the spinal cord due to degenerative joint disease of the articular process. Neck pain
(on palpation) is usually present, and maybe the most important clinical finding. Horses may actually present for a front
limb lameness due to compression of a nerve root. Other clinical signs may include focal muscle atrophy, focal sweating, or
palpable bony abnormalities of the articular processes.
Neuroanatomic location: Cervical Vertebrae with a focal distribution.
Standing cervical vertebral radiographs may be very helpful in certain cases. However, there are cases that will have normal
cervical radiographs and a myelogram is helpful.
Abnormalities include: 1) flare of the caudal vertebral epiphysis (more common in young horses) 2) abnormal ossification of
the articular processes (young horses); 3) malalignment between adjacent vertebrae (more common in young horses) 4) extension
of the dorsal laminae (young and old horses) and 5) degenerative joint disease of the articular processes (more common in
older horses and at C5-C6 and C6-C7).
Further assessment: measurement of the cervical vertebral sagittal ratios: an assessment of the width of the spinal canal
width. Must be lateral.
Myleography is required to confirm diagnosis of a focal spinal cord compression, and is necessary if surgical treatment is
Medical treatment: Medical treatment aimed at reducing swelling and edema with anti-inflammatory medications and rest.
Young horses less than one year of age: "pace diet"- restricts exercise, reduce diet to 80% of NRC. Make sure that trace minerals
are balanced (such as copper and zinc)
Adult horses: intra-articular injection of the facets with steroids will reduce inflammation, and improve pain. Done via ultrasound
Equine Protozoal Myelitis:
Signalment: any age
The clinical signs are highly variable. Asymmetric ataxia is the most common. Other clinical signs include asymmetric muscle
atrophy, and occasionally cranial nerve disease. Cerebral disease (such as seizures) is very rarely reported. EPM can range
in severity, from a mild gait abnormality to recumbency.
Can vary. Classical descriptions include a multifocal distribution, which often includes spinal cord and brainstem (cranial
nerve disease). However, it can present as a cervical vertebrae and with a focal distribution.
The clinical diagnosis remains a challenge. Diagnosis of EPM should include two facts: 1) the horse has clinical signs of
neurological disease and 2) clinicians should rule out as many other diseases resulting in similar clinical signs.
There must be signs of neurological disease that are consistent with EPM. This can be difficult in horses with mild gait abnormalities
(lameness versus mild spinal ataxia)
Ruling out other potential causes of EPM. The most common example would include horses with spinal ataxia, localized to the
cervical vertebrae. Cervical vertebral radiographs are indicated in these horses.