Today, I thought we'd take a deep dive into vestibular disease via a case discussion. Let's consider this 5 year old FS Lab X that is presenting to us with a history of a head tilt. The owner reports a sudden onset right head tilt, followed within 24 hours by ataxia (falling to the right, especially when turning) and reduced appetite. Believe it or not, it was the reduced appetite that worried this owner the most! :)
Physical exam: Unremarkable other than mild obesity
Neurologic examination:
Mentation: very BAR!
Cranial nerves: right head tilt, nystagmus at rest and faster when dorsiflexed but no change in direction. This is called a pathologic nystagmus but it is not positional. Mild anisocoria with miosis OD and incomplete dilation in dark. The remainder of the cranial nerves were normal.
Gait: moderate vestibular ataxia with frequent stumbling right, especially when circled. If you're unsure if this patient has a vestibular ataxia, consider going on uneven surfaces (grass) or turn off the lights. Navigating in the dark is MUCH harder without a good vestibular system!
Reflexes: Normal spinal reflexes
Postural reactions: normal in all limbs
Palpation: no evidence of pain on spinal palpation and normal cervical ROM, but she did seem head shy when I touched her ears.
First question: Does this dog have evidence of vestibular disease?
Yes! She has a head tilt, nystagmus and vestibular ataxia which are the hallmark signs of vestibular dysfunction. Other signs of vestibular disease could include a positional strabismus.
Second question: Where does this localize?
Localizing a vestibular lesion requires a quick refresher on anatomy (don’t stop reading!!). There are three parts to the vestibular system:
1. Peripheral (receptions in the ear, and the nerve)
2. Brainstem (nuclei in the brainstem)
3. Cerebellum (coordinating parts of the cerebellum)
When the brainstem component malfunctions, it isn’t just the vestibular system that stops working. We expect to see weakness (hemiparesis), proprioceptive deficits (unilateral paw replacement deficits) and/or reduced mentation (obtunded, stupor or coma). If you recognize one or more of these 3 signs ALONG WITH vestibular signs, the animal likely has a brainstem localization.
When the cerebellar vestibular component malfunctions it often ropes in gait deficits and tremors along with the vestibular signs. This means that the hypermetria and intention tremors become apparent. If you see hypermetria or intention tremors ALONG WITH vestibular signs, consider a cerebellar localization.
Lastly, if none of those additional signs are noted the lesion is localized to the peripheral component. That means we ONLY see vestibular signs and no signs of limb weakness, proprioceptive deficits, mentation changes, intention tremors or hypermetria!
So, what is the localization for the lab in this example? We don’t see any additional signs of neurologic disease that would localize to the brainstem or the cerebellum so this pet likely has a peripheral lesion localization.
Third question: What are the differential diagnoses?
For this patient, I would consider otitis media/interna, neuritis and less likely neoplasia.
Thanks for reading! I hope you are having a wonderful summer and soaking up all that your area has to offer this time of year! Please reach out if you have a case that you feel would benefit from a neurologic examination. Vestibular cases can often be evaluated by video consult if I cannot make it to your region.