The most important step in diagnosing vestibular disease in the cat is differentiating peripheral and central vestibular disease. Your veterinarian will perform a neurologic exam that will yield the most information of any diagnostic. He or she will examine both the vertical and horizontal canals and make an assessment of the ear drum. This can only be done with a special scope. Advanced imaging, such as CT or MRI scans, is used to evaluate the boney inner ear, brain and spinal cord. Basic blood work will assess thyroid function (though rare) and rule out any other serious signs of infection, organ dysfunction, or electrolyte disturbances.
The right (note labels at top of images) ear canal in this CT scan is open and free of disease. The left has soft tissue filling the middle-inner canal as noted by the arrow. On the right image shows a probably cancerous lesion (note the white arrows) in the brain (gray-black areas in center of image) that can present with vestibular signs.
Differentiating central and peripheral can be done by a number of means. If nystagmus is vertical (seen here), this is highly suggestive of central vestibular disease. In addition, positional nystagmus (nystagmus only present in when the cat is in certain positions) will also indicate central disease.
The direction of peripheral vestibular nystagmus helps identify the location of the lesion. The side that the eyes “run away” from is typically where the lesion is located. For example, the dog in this video’s signs suggest his lesion is on the right side, as the fast phase is to his left. Generally, this rule holds true with only a few exceptions which are not discussed here. Click here to learn more about the clinical signs of vestibular disease in the cat.
The other main exam finding that differentiates central/peripheral is conscious proprioception. This nerve pathway allows the brain to know where the limbs are in space without the visual pathway (incidentally, law enforcement agents use understanding of these pathways to look for intoxicated drivers by asking people to touch their nose with their eyes closed). Basically, your brain knows where your fingers, toes, arms, and legs are even when your eyes are closed. Conscious proprioception deficits will almost always be present in central vestibular disease. Even with these rules about nystagmus and CP deficits, a veterinary neurologist may be needed to sort out the source of the lesion.
Further workup for central vestibular disease will often include advanced imaging such as a CT scan or MRI. These advanced techniques allow for non-invasive investigation of the inner ear, brain, and spinal cord. A CSF (cerebral spinal fluid) tap will help diagnose inflammatory or infectious CNS disease.
Click here to learn about treatment options for cats who have been diagnosed with vestibular disease.