As we reflected on our familys, and leaned back in our chairs last week around the Thanksgiving table (sorry, Canadians, I know yours was last month) I thought - wait - vestibular disease in cats! (That, and why did I eat so much pie?) First, I have been asked "Do cats get vestibular disease?" The answer is: yes. They have the same anatomic structures and roughly the same neural pathways that influence the vestibular pathways as dogs do. Let's look at a case:
Signalment: 4 year old FS DSH
Neurologic Examination:
Mentation: normal
Cranial nerves: right head tilt, horizontal nystagmus FF left, positional strabismus OD, remainder of the cranial nerves are normal.
Reflexes: normal
Postural reactions: normal tactile placing all four limbs
Gait: ambulatory with mild vestibular ataxia and staggering right when turning.
Palpation: Non-painful spinal palpation and cervical ROM
Peripheral Vestibular Disease
The basic players in the peripheral system are 1) The receptors, 2) cranial nerve VIII or vestibulocochlear nerve. Cats with peripheral nerve disease may have a head tilt, nystagmus, positional strabismus, vestibular ataxia and falling/rolling. The head tilt is towards the side of the lesion. The nystagmus are a bit trickier. In the old days we used to track the direction of the nystagmus as a localizer. Remember when we said horizontal nystagmus indicated peripheral disease, vertical nystagmus indicated central disease and rotary was either? Welllll..... that isn't strictly true anymore. While it is true that horizontal nystagmus are typically associated with peripheral disease, they can be seen with central disease, too. The same is true for vertical nystagmus. Nystagmus that develops only when the head is placed in a specific position (positional nystagmus) are more common with central disease, but unfortunately are no longer strictly associated with that neuroanatomic lesion localization. So how do we localize peripheral disease?? We localize based on the lack of specific findings on the neurologic examination. What they won't have is ipsilateral paw replacement deficits, ipsilateral hemiparesis and/or reduced mentation (obtunded, stupor, coma). These last three findings are identified with brainstem vestibular disease ONLY.
Brainstem Vestibular Disease
The players in brainstem localization are the paired vestibular nuclei in the rostral medulla oblongata. The tracts for proprioceptive function, descending upper motor neuron and level of alertness (mentation) are also nearby. Therefore, if a disease in the brainstem is affecting vestibular function, it is also very likely to tick off one of those nearby pathways, therefore creating deficits. They don't need to have all 3 deficits, just one will do. So, a cat with a head tilt, nystagmus AND an ipsilateral tactile placing deficit is more likely to have a brainstem localization than peripheral disease.
Cerebellar localization
The last group of neurons influencing or being influenced by the vestibular system are the cerebellar nerves. In the cerebellum there are "marionette" nerves that exert their influence on the brainstem vestibular system. By "pulling strings" the cerebellar influences the output from the vestibular nuclei. Without this influence signs such as hypermetria, intention tremors and truncal swaying are noted. To localize to the cerebellum, signs of vestibular disease (head tilt, nystagmus, positional strabismus) are present PLUS hypermetria, truncal sway and intention tremors. When localizing to a specific side, follow the hypermetria. If an animal has hypermetria on the right front limb, the localization is right cerebellum. Occasionally delayed paw replacement is present, but this will be due to difficulty repositioning the limb rather than a solid paw replacement loss.
Have you figured out the neuroanatomic lesion localization for the case? That's right - peripheral vestibular disease! Differentials for cats are very similar to dogs with the exception that we see more polyps in cats, and more PSOM in dogs. Therefore, I would consider otitis media/interna, polyps, neuritis (infectious or inflammatory), hypothyroidism (yes, in a cat!), diabetes, and peripheral neoplasia. These differential diagnoses are then tailored to the specific case based on the history.
That wasn't too painful, was it? Let me know if you have a topic you think should be covered in a TidBit Tuesday!