VESTIBULAR DISEASE

“Milou,” a dog with vestibular disease, demonstrates a head tilt. At the time of this picture, Milou was not able to walk, but was nearly normal within 4 days. 

WHAT ON EARTH IS THE VESTIBULAR APPARATUS?

In a nutshell, 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: 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.

Rotation is detected using the three semicircular canals as shown above. These canals contain fluid called “endolymph” which moves as one’s head rotates. Tiny neurological hair cells project into this fluid and are stimulated by the flow. These hair cells are part of sensory nerves which carry the appropriate message to the cerebellum (part of the brain that coordinates locomotion) and to 4 vestibular nuclei in the brain stem.

Up and down orientation stems from small weighted bodies called “otoliths” which are located within the utricle and saccule of the middle ear. These small otoliths move with gravity within a gelatinous medium, stimulating small hair cells as they move similar to the situation described above.

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).

THE SIGNS 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. The movements will be slower in one direction. This is the side where the neurologic lesion is likely to be; however, nystagmus is named according to the direction of the fast component (i.e. there may be left nystagmus but the lesion is probably on the right side of the vestibular apparatus.)

• Circling (usually toward the side of the lesion.
• 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.

CAUSES OF VESTIBULAR DISEASE

The most common causes of vestibular disease are:

• Middle ear infection
• Brain lesion
• Idiopathic

In order to determine prognosis and choose treatment, one needs to figure out what has happened to the vestibular system. The first step is to determine whether the lesion is central (in the brain) or peripheral ( in the inner ear).

BRAIN OR CENTRAL LESION

IDIOPATHIC DISEASE

Canine idiopathic vestibular disease (also called "Old dog vestibular disease") and, its feline counterpart, feline idiopathic vestibular disease, begin acutely and resolve acutely. Usually improvement is evident in 72 hours and ]the animal is normal in 7-14 days, possibly with an occasional head tilt persisting. When a case of vestibular disease presents, it may be a good idea to wait a few days to see if improvement occurs before doing diagnostics beyond a routine blood/urine database. These two conditions are idiopathic, meaning we do not know why they occur. We do know that they represent problems in the periphery (nerves of the middle ear rather than in the actual brain.)

Treatment of idiopathic vestibular disease generally involves control of nausea (motions sickness) while the condition runs its (relatively short) course.

IDIOPATHIC VESTIBULAR DISEASE IS THE MOST COMMON FORM
OF VESTIBULAR DISEASE IN DOGS AND CATS.

FOR UNKNOWN REASONS, CATS ARE MOST COMMONLY AFFECTED IN THE NORTHEAST U.S. IN THE LATE SUMMER AND EARLY FALL.

MIDDLE EAR INFECTION

Middle ear infection is a likely possibility for vestibular disease especially if the patient has a history of ear infections. Concurrent facial nerve paralysis, creating a slackened look to one side of the face, or Horner’s syndrome, where there are some eye changes, often go together with middle ear infection.

When an otoscope is used to visualize the external ear of an animal with vestibular disease and debris is seen, this would be a good hint that there is infection in the middle ear as well. However, just because debris is not seen in the external ear does not mean that a middle ear infection is unlikely. Special imaging of the middle ear bones may be in order.

Treating a known middle ear infection can be difficult. Culture of the middle ear may be necessary and oral antibiotics are needed for 6-8 weeks to clear the infection from the tiny bones of the middle ear. Surgery may be needed to open the tympanic bullae and flush them out.

A WORD ABOUT “STROKE”

Vestibular signs are commonly (and usually wrongly) referred to as a “stroke.” It should be noted that while a vascular accident is a possible cause of vestibular signs, it is a rare cause. Vascular disease, while common in people, is unusual in pets. For more information about vascular accident in pets click here.

Page last updated: 3/29/2011