Vestibular syndrome is a common occurrence in dogs and catsand can be terrifying for pet owners.
Many pet owners believe their dog or cat has suffered a stroke. Stroke is actually a less-common cause of vestibular disease in pets.
The vestibular system is the major sensory system that participates in the maintenance of balance. It has both central (brain and spinal cord) and peripheral (trunk and limb) components.
Central lesions are located in the brain (medulla or vestibulocerebellar components).
Vestibular syndrome with a peripheral cause is usually easier to diagnose and carries a better prognosis than central lesions. Accurate diagnosis of central lesions may require advanced equipment, such as magnetic resonance imaging (MRI).
Three characteristics are common to both peripherally- and centrally-affected vestibular syndrome patients:
- Head tilt, which is usually toward the affected side.
- Ataxia (falling, rolling and circling), again usually in the direction of the affected side. Circling is often “tight” (small circles).
- Pathologic nystagmus and positional strabismus. Pathologic nystagmus is abnormal movement of the eye(s) that can occur side-to-side, up-and-down or rotatory (oscillating in an arc on the central axis of the eye). Positional strabismus is evidenced as a stationary movement of the eye to an abnormal angle when the head is moved.
Patients with peripheral vestibular disease may stagger, but they are not weak. They are aware of their position and surroundings, even though their reactions and responses may be abnormal. Horner’s syndrome, causing sagging in the face, can sometimes be seen because of effects on the facial nerve.
Patients with central vestibular disease will have head tilt, altered consciousness, paralysis in two or four legs, multiple cranial nerve deficits and be unaware of where their feet are (proprioception deficits). They may be weak and unable to stand.
Exceptions to the above “rules” also exist. Paradoxical vestibular disease is a central form of the syndrome that doesn’t fit the expected pattern.
Bilateral vestibular lesions, although causing abnormal gait and behavior, tend to balance each other out, resulting in a patient with little disturbance of equilibrium, but taking a low, crouching stance with feet spread wide apart. The head may sway back and forth. Bilateral vestibular disease occurs more commonly in cats.
Central vestibular disease can be a medical emergency, because its causes are often related to encephalitis, stroke or cancer inside the skull. Patients not quickly and correctly diagnosed and treated will often suffer irreversible brain damage. A notable exception is toxicity from metronidazole overdose, which carries a good prognosis and rapid resolution with medication.
See you next week, Dr. Randolph.
Our thanks to Dr. John Rossmeisl, Professor of Small Animal Internal Medicine and Neurology at the Virginia-Maryland Regional College of Veterinary Medicine, who presented this topic at a recent Louisiana Academy of Veterinary Practice meeting. MMVEST