Management of Horses Suspected to Have Spinal Cord Diseases - with an Emphasis on Cervical Vertebral Malformation

Lesions resulting in tetraparesis, paraparesis and ataxia of the limbs occur in the spinal cord, spinal nerve roots and ganglia, and neural plexuses and nerves of the limbs. If following the neurologic evaluation, cerebellar involvement can be ruled out in a particular wobbler case showing ataxia and weakness of the limbs then the clinician must attempt to differentiate between the remaining disorders producing degrees of tetraparesis, paraparesis, and episodic weakness to arrive at a diagnosis. With brain stem diseases there usually are signs such as somnolence and cranial nerve functional abnormalities. Patients having signs consistent with diffuse weakness due to lower motor neuron and neuromuscular diseases, either static, episodic or exercise associated, may also have evidence of cranial nerve dysfunction but should remain bright and alert and not demonstrate ataxia. However, with profound weakness, it can be very difficult to determine the presence or not of ataxia, particularly if the patient is very reluctant to move.
Several diseases and syndromes are not emphasized here because of their parochial or rare nature or because of their uncertain clinical and neurological significance. However, the interested reader can refer to such examples as degenerative disk disease, ionophore and salinomycin toxicosis, and snakebite etc.
Spinal cord disease is common in horses. A horse showing variations of ataxia and weakness is called a wobbler and should be used as a generic term, not defining the cause of the syndrome, although some people equate the term wobbler with the disease cervical vertebral malformation. With a mild or even moderate cervical spinal cord lesion in an adult horse, especially when chronic, signs of ataxia and weakness may only be evident in the pelvic limbs only, especially if the patient is uncooperative. In this situation, and with no evidence of brain stem or cerebellar disease, it is safest to conclude that the patient has a lesion between C1 and S3. On the other hand, close scrutiny of the gait, posture and postural responses in the limbs, along with a search for localizing findings, often is productive. As a general rule, large patients that sit with forelimbs extended and supporting weight for several minutes most likely have a lesion caudal to T2. By being able to accurately define the site of the lesion, the clinician can reduce the number of possible diseases to be considered and thus can better direct the ancillary testing that is available. Spending prolonged periods upright but resting on the knees with the carpi flexed is very foreign to horses and even with profound thoracic limb weakness they will position themselves with the forelimbs extended and locked for support. This compares with marked extensor weakness in the pelvic limbs when a crouched posture with the pelvic limbs held forward is adopted.  [...]