Loss of vestibular function in both labyrinths leads to characteristic dysfunction in vision and balance. These symptoms reflect how crucial our labyrinthine sense is for generating the proper reflexes so that we can see clearly when we are moving, and not lose our balance when we are standing or walking.
Oscillopsia - the illusion that the environment is moving when we move our heads - is the characteristic visual symptom when vestibular function is lost. Oscillopsia often occurs when riding in a car, especially when the road is bumpy. This can make reading street signs difficult unless the car slows or stops. Oscillopsia also occurs when running, or walking quickly, which can make it difficult to recognize faces when on the move. Oscillopsia can occur when quickly turning the head, such as during driving when you check to see if cars are approaching from a side street, or when simply scanning across a computer screen.
These symptoms are skillfully described in an article called, "Living Without a Balance Mechanism", published in the New England Journal of Medicine in 1954 and written by a physician named J.C. who himself lost labyrinthine function as a toxic side effect of an antibiotic. Initially, J.C. could not read without the words on the page bouncing up and down about once per second due to the transmission of the pulse of his heart to his head. Without a labyrinthine sense, his brain could not compensate even for the small head bobs produced by the pumping of the heart. At first, J.C. had to hold his head still between his hands when he tried to read from a book. Fortunately, J.C. learned to compensate for his loss and made a marvelous functional recovery that he beautifully describes.
The other major symptom of the bilateral loss of labyrinthine function is imbalance with a susceptibility to falls. Imbalance is especially brought on when rapid readjustments in posture are required such as when making a quick turn around a corner. Imbalance also occurs when a patient is deprived of other sensory cues that are typically used to compensate for the loss of labyrinthine function. Walking in the dark can be particularly treacherous because information from vision is no longer available to help with balance. Likewise, walking on sand, soft grass, or wet ground or even a soft rug becomes difficult because sensations from the feet cannot be used to determine exactly where one's feet are relative to the stable ground. For these reasons, patients with a loss of bilateral labyrinthine function should never swim alone, especially at night or on a cloudy or dark day, because when they are under water, they may not be able to sense up from down due to the lack of visual and other sensory cues.
In some circumstances, the visual cues that some patients must rely upon to compensate for a loss of labyrinthine function are improperly interpreted. For example, on a windy day, the swaying of large trees may cause patients with labyrinthine dysfunction to lose their balance. Their brains misinterpret the swaying of the trees as swaying of their bodies. They try to make an adjustment in posture, which is not what they actually needed. Even individuals with perfect labyrinthine function can experience similar abnormal sensations. We all have experienced the strange feeling of movement when we're actually quite still. For example, when watching another train go by while our train is sitting perfectly still in the station. For patients, the use of visual cues as a substitute for the loss of labyrinthine function is usually a good thing, but considerable movement of other people or objects in the environment can become quite uncomfortable and disconcerting. Examples include watching people in a crowd as they are rushing by, moving down the isles quickly in a grocery store, or viewing an action packed movie.
Patients who lose labyrinthine function in both ears at the same time usually do not have the sustained sense of spinning or falling with nausea and vomiting as do patients with an acute loss of labyrinthine function from just one ear. Such severe symptoms arise from patients with a unilateral loss of function because even when the head is still there is an imbalance in the normally equal and even flow of sensory signals that come to the brain from each labyrinth. In contrast, patients who have a bilateral loss of function have no asymmetry of activity from the two labyrinths with the head still and hence do not have symptoms until they move. In fact, some patients who lose vestibular function, for example from the toxic effects of some antibiotics that must be used to treat some severe infections, are so sick otherwise and move so little that they are unaware of any balance or vision problems until they recover from their infection and start moving around more normally. So, while patients with a unilateral loss of function can be quite sick initially, the recovery and adaptation to their problem is usually more rapid and complete than that made by patients with a loss of vestibular function from both ears.
Causes of Bilateral Loss of Vestibular Function
- Severe head injuries
- Certain infections, especially meningitis in children or viral
- Hereditary symptoms, sometimes associated with migraine
- Menieres syndrome, which is due to an increased pressure in the fluid in the inner ear
- Inflammatory conditions
- Autoimmune diseases
Sometimes, there is no apparent cause. One of the more common causes of the loss of labyrinthine function is a toxic side effect of antibiotics such as gentamicin. Gentamicin is an important antibiotic used in severe and life threatening infections, but it has the unfortunate side effect that in a small percentage of patients, it poisons the inner ear cells and leads to a loss of vestibular function. There is probably a genetic predisposition to developing this side effect so that patients may lose labyrinthine function even though the drug may not have been used in an excessively high dose or for an excessively long time. Gentamicin only rarely affects hearing, which also makes its toxicity difficult to detect. The loss of vestibular function may be insidious, and elude detection for many days, or even weeks - especially in a sick patient who is confined to bed and is not moving around.
The ability to recover from a bilateral loss of labyrinthine function depends upon many factors, including:
- The speed at which function is lost. The slower the loss, the more readily the brain can adapt to compensate for it.
- The age the patient is when the function is lost. Younger people can adapt easier.
- The amount of function that survives. The more function that is left, the easier it is to compensate.
A few years back, as part of a research project, we examined a patient who had lost all labyrinthine function as a child. Nevertheless, he became an outstanding athlete and state javelin champion. Unfortunately, many patients lose their function when they are older. While there is no hard rule about age and recovery, patients who lose their labyrinthine function after they reach the age of 50 tend to have more difficulty compensating for it.
The hallmark of therapy is a program of physical rehabilitation specifically designed by a vestibular rehabilitation specialist and based upon the degree and type of deficit. Depending on whether function is either partially or completely lost, the therapy program will emphasize improving upon what labyrinthine function remains or on developing alternative strategies using other sensory cues such as from the neck, feet or eyes that can substitute for the missing sensations from the labyrinth. Tai Chi or Chinese exercises may also help patients regain balance. Particularly helpful in guiding the physical therapist are the results of vestibular testing, including high speed rotations in a chair, and posturography which tests one's balance on a moving platform. Finally, one should not underestimate the amount of mental effort, energy, and concentration it takes to maintain balance when the labyrinthine sense is absent. Imagine how hard it would be for any of us to walk on a balance beam for an entire day. Patients who have lost labyrinthine function must constantly pay attention to their balance and make an effort to keep it. They do not have the automatic, subconscious reflexes that people with normal labyrinthine function have and about which they never have to think.
Maintaining balance can be extremely fatiguing for patients with vestibular loss and saps their energy. Nevertheless, most patients report that with time and physical therapy, they learn to live with their problem. They know it is still there, but they have developed compensatory strategies that allow them to cope successfully with their disability and to return to rich and productive lives.