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Vestibular Disease
Tammy Stevenson, DVM, DACVIM (Neurology)

Veterinary Specialty Hospital, San Diego, CA, USA

The term vestibular disease is used to describe a neuro­ position relative to gravity and with movement, and
anatomic localization within the vestibular system of any appropriate limb tone and position relative to gravity
cause, and therefore, is not a specific diagnosis. and head position. Dysfunction results in head tilt, and
The purpose of the vestibular system is to provide imbalance in extensor tone such that the animal leans
balance by adjusting limb extensor/flexor tone to accom­ or circles to the side with less tone.
modate for changing head and body positions. This results ● Projections to the vomiting center (in the reticular for­
in controlled and coordinated eye‐head‐trunk‐limb mation) leading to ptyalism, inappetence, and vomiting.
movement with proper postural support. ● Projections to the cerebral cortex to provide conscious
The structures of the vestibular portion of the inner ear awareness of the body’s position in space via the
include semicircular canals that are responsible for con­ thalamus (pathway not well identified), and awareness
veying information regarding acceleration in angular of dysfunction such that the patient may “feel bad.”
planes, and the utriculus and sacculus which convey infor­ ● Projections to the cerebellum (via the caudal cerebellar
mation regarding linear acceleration and static head posi­ peduncle, in the vestibulocerebellar tracts) which may
tion (relative to gravity). Information from these receptor result in decreased extensor tone on one side of the
organs travels via the vestibular portion of the vestibuloc­ body and increased tone on the other (leaning).
ochlear nerve (CN VIII) to the vestibular nuclei (four on As with all problems involving the CNS, the location of
each side of the brainstem – rostral, caudal, medial, and the lesion, not what caused the lesion(s), determines the
lateral), through the caudal cerebellar peduncle, to the signs you see. Therefore, a thorough neurological exami­
flocculonodular lobes of the cerebellar hemisphere. The nation is critical to proper localization and an accurate
dorsal spinal nerves of C1–3 provide input to head posi­ differential list which, in turn, guides the diagnostic plan.
tion and balance and can also cause vestibular signs when
dysfunctional.
Dysfunction of one or more parts of the vestibular
system may result in the signs we classically recognize as Peripheral versus Central Disease
“vestibular disease” – a head tilt, nystagmus, walking in
circles, ataxia/falling or even rolling, abnormal limb For vestibular disease, the first step is differentiating
extensor tone, and nausea/vomiting. These signs are due peripheral from central disease. Peripheral vestibular
to the vestibular system’s extensive connections with disease is characterized by a head tilt and circling towards
various parts of the central nervous system (CNS). the side of the lesion, and pathological nystagmus with
the fast phase away from the lesion. Unfortunately, cen­
Projections via the medial longitudinal fasciculus to
● tral vestibular disease cannot be definitively ruled out on
the nuclei of CN III, IV, and VI which control the exam alone. However, any of the following abnormalities
extraocular eye muscles. In homeostatic conditions, can lead to a confident central localization.
these connections result in normal physiologic nystag­
mus (oculocephalic reflex), and with dysfunction, ● Cranial nerve deficits other than VII or VIII. Deficits
pathological nystagmus. associated with VII or VIII alone can be seen with both
Projections via the vestibulospinal tract, to the neck, peripheral and central disease, as can sympathetic dys­
●
trunk, and limbs, resulting in appropriate head/neck function (Horner syndrome). Involvement of other

Clinical Small Animal Internal Medicine Volume I, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical