Vestibular Disease
What is the Vestibular Apparatus? Why is it a disease?The vestibular apparatus is the neurological equipment and wiring responsible for perceiving the body's orientation relative to the earth. It determines what is up, what is down, if you are upside-down, standing up straight, falling and informs your eyes and extremities to move to get back to the center orientation. The vestibular apparatus signals us to when we need to right ourselves, to walk and even run over uneven ground without nose diving. This mechanism allows our eyes to follow moving objects without becoming dizzy. Well some better than others.There are two different sets of receptors involved: The first one detects tumbling or turning (rotational acceleration, horizontal or vertical). Carnival rides are a good examples turning: (merry go round) and tumbling more of a Ferris wheel action. The second one detects straight line (linear acceleration) and gravity, forward / backwards or vertical. Examples: falling (vertical) lets us know which direction is up and which is down. A Navy plane being catapulted across the deck is a forward acceleration example.
Both sets of receptors are located in the middle ear. Tiny cilia (neurological hair cells) project into specific canals of fluid so that when your head moves, the fluid moves, and the hair cells wave within the fluid. These hair cells are part of sensory nerve system that transmits the appropriate message to the cerebellum (the brain part coordinating locomotion) and to the four vestibular nuclei in the brain stem. Instructions are carried from these centers by nerve cells to the leg and neck muscles and eye muscles so there is immediate orientation. The information received about being upside down, or some other abnormal orientation, is sent to the hypothalamus (an area of the brain) so that we can become consciously aware of our position. This information is integrated such that if you would have to think about which response or action to take it would be too late.
Information is sent to the "reticular formation" in the brain. The reticular formation acts similar to a volume control for our state of wakefulness. If we are asleep and start to fall, the vestibular simulations from sudden change should wake us up. Veterinarians use this when rolling an anesthetized animal from side to side to hasten anesthetic recovery. The Signs of Vestibular Disease
Animals with vestibular disease, usually demonstrate a head tilt and a weird eye motion reminding owners of a stroke. When it first starts people think it is a stroke. I have seen cases where animals are presented prior to nystagmus. Usually there is some improvement in 4-7 days.
When there is trouble in the vestibular apparatus, one may not properly perceive their orientation. You don't know which way is up, unable to differentiate standing up straight or slanted, and you feel dizzy. Signs of vestibular disease:
Ataxia: lack of coordination, no weakness or involuntary spasms, stumbling and staggering.
Motion sickness
Nystagmus: back and forth or rotational eye movements of the eye. Movement is slower in one direction. This is the side where the neurologic lesion is. Nystagmus is named by the direction of the fast component. Left nystagmus as seen on animal the lesion is probably on the right side of the vestibular apparatus.
Circling Head tilt indicates the side with the lesion. Falling to one side, toward the side of the lesion Trouble with nerves that control the head and face
Causes of Vestibular Disease: To determine prognosis and treatment, one needs to figure out what happened to the vestibular system. First determine whether the lesion is central (in the brain) or peripheral (in the inner ear). There are some hints in a clinical presentation. For example, if cranial nerves are involved and they are opposite from the head tilt, the lesion is likely to be in the cerebellum (central). If nystagmus is vertical (eyes are moving up and down rather than back and forth) or only exists when the animal is placed in certain positions (positional nystagmus), the lesion is more likely to be central. Canine idiopathic vestibular disease, old dog vestibular disease, and the feline counterpart, feline idiopathic vestibular disease, begins acutely and resolves quickly. Some improvement is seen in 72 hours and the animal is almost back to normal in 7 to 14 days. There is the possibly of head tilt persisting. IN cases of vestibular disease, it may be a good idea to do routine blood and urine database and wait a few days to see if improvement occurs. If improvement does not happen further imaging may be warranted.
Idiopathic Vestibular Disease is the most common form of Vestibular Disease in dogs and cats. Idiopathic by medical definition means we do not know the cause. They represent problems in the periphery, the nerves of the middle ear rather than in the actual brain.
Middle ear infection is possible for vestibular disease especially if a patient has a history of ear infections. An otoscope is used to visualize the external ear of an animal with vestibular disease and if debris is seen this is a good hint that infection is in the middle ear as well. Debris not seen in the external ear does not mean a middle ear infection is unlikely. Imaging of the middle ear bones may be in order. To evaluate the middle ear a set of radiographs called a bulla series is needed. This focuses on an ear bone called the tympanic bulla. If the bulla is abnormal, the ear(s) may require surgical drainage. X-rays may not be sensitive enough to pick up damage in the middle ear. A normal set of films does not rule out disease. Special imaging such as a CAT scan or MRI is better method of visualizing and diagnosing, although pricey. These imaging techniques, allow imaging of the brain tissue itself thus allowing brain abnormalities to be evaluated as well. Brain tumors are a cause of vestibular disease, if the signs fit with a central lesion. In these cases, imaging is needed to make a diagnosis. Some tumors may be treatable depending on their location.If a pet has an unknown middle ear infection, a routine home or in clinic cleaning of an external ear can lead to a flare up of vestibular signs. In long-standing ear infections this may repeatedly happen.
There are palliative medications that can help a primary vestibular case get through the nausea of a rapidly spinning world. They usually do recover very well. Repeated episodes can be expected.