Anyone who takes a fast spin on a merry-go-round can appreciate vestibular disease in a cat. Cats have a remarkable ability to stalk, hunt, run, and land on their feet with ease. This is due to coordination of the primary sensor system maintaining balance and normal body orientation relative to the earth’s gravitational field. A disruption of this finely tuned nerve control can lead to a loss of equilibrium.
Common signs of vestibular disease are ataxia (lack of coordination or balance), head tilt, circling, falling to one side, nausea (motion sickness), strabismus (deviation of the eyeball), and nystagmus (back and forth, up and down, or rotary eye movements). The cat will usually fall, circle, or tilt the head toward the side of the body where the primary lesion is located.
When vestibular disease is suspected, it must be determined if it involves the inner ear (peripheral) or the brain stem (central). In addition, the signs can be unilateral (one-sided) or bilateral (both sides affected). Cats with bilateral peripheral disease appear weak because of a sense of disorientation; yet the muscles of their limbs have normal strength. If central vestibular disease is present, there will be deficits in such postural reactions as limb placing and proprioception (positioning), along with a diminished mental awareness (depression or decreased consciousness). A paradoxical form of central vestibular disease affects the opposite side of the body from the lesion. Evaluation for cranial nerve deficits may exhibit a loss of facial sensations or movements.
A common form of peripheral vestibular disease is otitis media or interna (middle or inner ear). Bacterial infections can result from an extension of disease in the external ear or the upper air passages by way of the auditory tube. Nasopharyngeal polyps and cancerous growths can be found in these same areas. Ear cleaning can lead to vestibular signs due to over-stimulation or inflammation of the eardrum and deeper ear structures. The use of certain drugs, such as aminoglycoside antibiotics, and the overdose of other medications such as metronidazole can be toxic to inner ear tissue. Deafness could be the end result in some cats.