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What is vestibular disease?
The vestibular apparatus
is the neurological equipment responsible for perceiving one's body's
orientation relative to the earth (determining if you are upside-down,
standing up straight, falling etc.) and informing
ones eyes and extremities how they should move accordingly. The
vestibular apparatus allows us to walk, even run, on very uneven ground
without falling, helps us know when we need to right ourselves, and
allows our eyes to follow moving objects without becoming dizzy.
There are two sets of
receptors involved in the vestibular apparatus: one to detect rotational
acceleration (tumbling or turning) and one to detect linear acceleration
and gravity (falling and letting us know which direction is up and which
is down). Both receptors are located in the middle ear. Tiny
neurological hair cells project into special canals of fluid so that
when one's head moves, the fluid moves, and the hair cells wave within
the fluid. The hair cells are part of sensory nerve cells, which carry
the appropriate message to the cerebellum (part of the brain that
coordinates locomotion) and to 4 vestibular nuclei in the brain stem.
From these centers,
instructions are carried by nerve cells to the legs and neck muscles,
and eye muscles so that we may orient ourselves immediately. The
information about being upside down (or in some other abnormal
orientation) is also sent to the hypothalamus (an area of the brain) so
that we can become consciously aware of our position. The information is
also sent to the "reticular formation" (another area of the brain - a
sort of a volume control on our state of wakefulness. In this way, if we
are asleep and start to fall, the vestibular stimulations would wake us
up. This is also why rolling an anesthetized animal from side to side is
used to hasten anesthetic recovery).
What are the symptoms
of vestibular disease?
If there is trouble in the
vestibular apparatus, then one may not properly perceive one's
orientation. To
 put
it more simply, one won't know which way is up, whether or not one is
standing up straight or slanted, and one will feel very dizzy.
The following are signs of
vestibular disease:
-
Ataxia (lack of
coordination without weakness or involuntary spasms - in other
words, stumbling and staggering around)
-
Motion sickness
-
Nystagmus (back and
forth or rotational eye movements
-
Circling
-
Head tilt (usually
toward the side of the lesion)
-
Falling to one side
(usually toward the side of the lesion)
-
Trouble with other
nerves controlling the head and face
What causes vestibular
problems?
Vestibular disease can
come from problems in the brain (infection, stroke, or tumor) itself
affecting the areas mentioned above. Or, it can occur due to disease
(infection or tumor) in the inner ear. Both dogs and cats can get a
form of this disease that has no known cause, but comes on very quickly
(Idiopathic vestibular disease)
How do we diagnose
vestibular disease?
Diagnosis of this problem
begins with a thorough history, physical and neurologic examination.
Certain aspects of the neurologic exam can help the veterinarian
determine if the problem is in the brain or in the inner ear (sometimes
it is not possible to make this determination). If an inner ear
infection is suspect, radiographs of the skull can be taken which may
document the problem. Sometimes, fluid will be aspirated from the
middle ear (through the ear drum) to be submitted for analysis and
culture.
If a brain lesion is
suspected, a cerebro-spinal fluid tap may help with the diagnosis or an
MRI (magnetic resonance image) may be performed.
Pets with vestibular
disease vary in their symptomatology. Some pets have just a minor head
tilt and may be treated as an outpatient after appropriate diagnostics
have been run. Others are so dizzy that they are rolling and vomiting.
These pets must be supported with intravenous fluids, anti-emetics and
supportive care until the vestibular crisis passes. Definitive
treatment depends on the cause of the problem. Ear related problems
require surgery to remove the infection or tumor from the middle ear.
This is done by way of a surgery called a bulla osteotomy or a total ear
ablation. This surgery may have side effects including facial nerve
paralysis (temporary or permanent) and infection, but generally, it is
the best chance to help the ailing pet. Pets suffering from idiopathic
vestibulitis may improve with anti-inflammatory and anti-nausea drugs.
What is the prognosis for vestibular disease?
The prognosis for
vestibular disease varies with the different causes. Idiopathic
vestibulitis is one of the most common causes and holds a pretty good
prognosis. Most pets will improve over 3-7 days and go on to live a
normal life (although a residual head tilt is common). Inner ear
infections may require surgery to relieve symptoms. This usually means
sacrificing the middle ear, but usually, these pets have already lost
hearing in that ear. If the surgery is successful, these pets should go
on to live a normal life (although a residual head tilt is possible).
Brain lesions such as strokes and tumors hold a much more guarded
prognosis. Some tumors are surgically removable while others may
improve with radiation and/or chemotherapy.
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