Microsoft word - vestibular disease
What is the vestibular system?
The vestibular system is the sensory system that functions to maintain an animal's balance
and normal orientation relative to the earth's gravity. It has two main functions: 1) To
maintain balance by stabilizing the position of the head in space and 2) maintaining a
steady visual image by stabilizing the eyes during head movement. The sensory receptors
are located in the inner ear. The receptors send messages to parts of the brain involved in
coordinating balance, specifically the brain stem and cerebellum. There is extensive
integration of neural information that leads to coordinated eye movements, proper head
and limb position and normal limb tone. What are signs of vestibular disease?
When the vestibular system is malfunctioning common signs include a head tilt, nystagmus
(rhythmic eye twitching), circling/falling/rolling in one direction, and/or
nausea/vomiting/inappetence. Some patients may also have other signs depending on
where in the vestibular system the problem is located. For example, patients with an inner
infection may have a small pupil or a protruding third eyelid on the affected side. Peripheral vs. Central Vestibular Disease
The neurological examination becomes an important tool for localizing the problem to either
the inner ear (peripheral vestibular disease) or a problem inside the brain (central vestibular
disease). Historical information provided by you, in combination with the neurological
examination, help to define the more likely causes for the vestibular disease in an individual
patient. Diagnostic testing
Diagnostic tests recommended for patients with vestibular disease depend on the history,
breed and age of the patient and whether the problem appears to involve the peripheral or
central vestibular system. Testing may include one or more of the following: looking down
the ear canal with an otoscope, basic blood work and urine analysis, a serum thyroid level,
blood pressure, chest x-rays +/- abdominal ultrasound, advanced imaging of the vestibular
system (MRI or CT scan), cerebrospinal fluid analysis, and possibly a Brain stem Auditory
Evoked Response (BAER) test (special electrical testing of the inner ear and brainstem). Common causes of Peripheral Vestibular Diseases
Ear infection (Otitis Media-Interna): This is a common cause of peripheral vestibular
disease in dogs and cats. This is usually caused by a bacterial infection in the middle ear
that travels to the inner ear. Affected animals may or may not have signs of external ear
infection such as head shaking, rubbing or scratching at the ear(s), and pain. Chronic ear
infections may lead to other nerve problems causing facial weakness and Horner’s
Syndrome (a small pupil, retracted globe, and a protruding third eyelid) on the affected
side. Depending on the severity of the problem, treatment may involve medical or surgical
management. Clinical signs may still be present after resolution of infection due to
Canine Idiopathic Vestibular Syndrome (aka “Old Dog” Vestibular Disease): This is also a
common cause of peripheral vestibular disease in dogs. This disorder usually seen in older
dogs but dogs of any age may be affected. Idiopathic means that the cause for the disease
is unknown. Patients develop a sudden onset of a head tilt, eye twitching, “drunken” gait or
may even be unable to rise when severely affected. They may also vomit due to the
motion sickness caused by the imbalance of the vestibular system. There is usually
spontaneous recovery within a few days to weeks, although residual signs such as a head
tilt may persist. Many dogs cannot eat or drink on their own because they have difficulty
maintaining an upright posture and may require extensive nursing care in the short term.
There is no specific treatment, however, some patients will benefit from antinausea
medication, valium, intravenous fluid support, +/- nursing care for patients that can’t walk on
their own. Rarely dogs may have future vestibular episodes.
Feline Idiopathic Vestibular Syndrome: This can occur in cats of any age and affects
outdoor cats more frequently. It is more common in the summer and fall months. Clinical
signs are similar to canine idiopathic disease although vomiting is not common. Diagnosis
is based on exclusion of other causes of peripheral vestibular disease. They also
spontaneously recover within a few weeks.
Nasopharyngeal Polyps: This is common in cats 1 to 5 years old. A polyp is a fleshy-like
mass that originates from the auditory tube or the wall of the middle ear. It can cause
secondary infection or inflammation of the middle and inner ear. The patient may also
present with signs of sneezing and gagging since the polyp can grow into the back of the
throat. Polyps can usually be removed surgically but they may recur. The prognosis after
surgical correction is good.
Other causes of peripheral vestibular disease are cancer in the ear canal and drug toxicity
(topical drugs placed in the ear).
Even when animals do not recover fully from peripheral vestibular syndrome they usually
have good quality of life. Central Vestibular Disease
Brain tumors, stroke-like events, drug toxicities (such as metronidazole and ronidazole),
nutritional deficiencies, infections (such as Distemper, Feline Infectious Peritonitis,
Toxoplasma gondii, Neospora caninum, and fungal infections) or diseases that cause
inflammation of the brain (such as granulomatous meningoencephalitis), are common
causes for central vestibular disease in both the dog and the cat.
If your veterinarian or veterinary neurologist suspects central vestibular disease, further
diagnostics will be needed to initiate appropriate treatment.
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