Unilateral vestibular loss (UVL) is one of the more common pathologies involving the inner ear and the nerves related to it. UVL makes up about 14-20% of all inner ear pathologies. People with an uncompensated UVL report symptoms in a great variety of ways, such as: wooziness, lightheadedness, motion sickness, feeling funny in the head, etc. These symptoms are commonly provoked or worsened by head movement.
What is a Unilateral Vestibular Loss, and what causes it?
A Unilateral Vestibular Loss (UVL) is a one-sided weakness in the balance mechanism of the inner ear. The weakness can occur suddenly or gradually, depending on the pathology or situation that has caused the weakness. The amount of vestibular loss can differ depending on what has caused the loss: a person can have a partial or a complete loss of the balance mechanism. Many different disease processes or surgical interventions can cause a total or partial UVL including (but not limited to): Meniere’s disease, vestibular neuritis, labyrinthitis, trauma, acoustic neuroma removal, and superior canal dehiscence repair.
The vestibular system is comprised of: the inner ear or vestibule, the vestibular nerve and the vestibular nuclei, which are located in the brainstem. The vestibular system is a paired system, meaning there are two: one on the right and one on the left. The vestibular system is one of three sensory systems we use to maintain our balance and equilibrium. The others are the visual system and the somatosensory system (information from your joints and muscles.) The inner ear picks up the sensory information about direction, speed, and duration of movement, and sends it through the vestibular nerve to the vestibular nuclei in the brainstem. The brainstem then takes the information, compares the information from the right and left inner ear, processes it, and sends appropriate commands to the eyes and postural muscles of the spine and legs to ensure we maintain an upright position, or maintain our gaze on objects in the environment.
To understand what happens after a UVL, we must first understand a little bit about how the inner ear works. The vestibular system has what is called a “resting level.” This is the level of activity that is generated by the inner ear even when our bodies are not moving. The resting level of an intact vestibular system is symmetrical, or equal, when you are sitting quietly. An active person has a higher resting level than that of a sedentary person. Think about what happens when you are ill with a cold. You rest more than usual to allow your body to heal. When you begin to feel better and start moving around again, you feel dizzy. This is because the resting level of vestibular function has temporarily reset to a lower level. After a few days of activity the resting level is higher, and you are no longer dizzy when you move.
When a UVL occurs, either the receptor (the inner ear) or the transmitter (the vestibular nerve) can be affected. So, either one inner ear generates a lower than normal signal, or one nerve transmits a lower signal than the other. The resting level of vestibular activity is then asymmetrical: there is a stronger response from one ear compared with the other. This asymmetry usually only occurs when your head or body is moving. Thus, conflict is created between the (now incorrect) information your vestibular system inputs (mobility), and with what your other systems perceive (stability). In this situation you might feel a sense of movement even when you’re motionless. The brain stem’s vestibular centers are preset to interpret particular signals from the inner ear as representing specific motions: asymmetry means motion. The preset doesn’t change, however, when the function of the inner ear changes. The conflict gets worse when you move because the asymmetry increases.
What are the symptoms of a UVL?
Initially, you may experience vertigo (a spinning sensation), imbalance, dizziness, and nausea or vomiting. The onset of these symptoms can be abrupt. Again, these symptoms are due to the asymmetrical inputs from the inner ears, which now are in conflict with your body’s visual and sensory systems. The symptoms usually begin suddenly, and gradually disappear over the course of a few days to a few weeks. You 
may be unable to work or be active during this time period. Most individuals with a UVL fully recover within 6-8 weeks. Although the asymmetrical signals from the inner ear remain, and the brainstem’s vestibular center’s preset level does not change, the brain’s response does change. As time goes by, your body begins to accommodate to the vestibular loss. Your brain practices postural and balance responses and over time learns how to send the proper signals to your muscles based on the new (asymmetrical) resting level of information from the vestibular system.
Although most people fully recover without medical intervention or therapy, some people are still troubled with dizziness and imbalance with rapid head or body movements. Still others are plagued with a constant sense of disequilibria. There is some evidence to suggest that people with a UVL are more sensitive to environmental stimuli (noise, crowds, visual patterns) than those without a loss. Some people also experience difficulty concentrating and thinking, which may persist to some extent even after the symptoms of dizziness and imbalance abate.
How is a UVL treated?
During the initial phase of a UVL, your doctor may prescribe medications to decrease the nausea and vertigo. Some examples are: Valium, Meclizine and Zofran. A short course of steroids is sometimes beneficial if an infection has caused the UVL. These medications should only be used during the first week or so of symptoms. After that period, research has shown that the long-term use of medications slows down recovery.
If symptoms persist after a few weeks and do not appear to be improving, diagnostic testing may be recommended. This can help your physician determine the nature and extent of the damage to the vestibular system, and also provides a baseline assessment of your balance. Your doctor may ask you to get a test called a VNG or ENG (Video-nystagmography or Electronystagmography.) A VNG is performed using a special infrared camera system to record eye movements during the test. An ENG performs the same tests, but the eye movements are measured with small electrodes placed around the eyes. Usually an audiologist will perform this test. Your physician may have an audiology department in his/her office, or you may need to go to a special clinic. The VNG (ENG) can determine how well the inner ear is picking up balance information, how well the vestibular nerve is transmitting the information, and how well the central vestibular centers in the brainstem are interpreting the information. The test can also help determine which inner ear is affected. Another test, called the Rotational Chair, can assess how well your brain has accommodated to a UVL.
Depending on the results of the testing and the improvement of your symptoms, vestibular rehabilitation may be recommended. This is a special form of physical therapy that is designed to help you accommodate to the loss of vestibular input from the affected inner ear. Your therapist will design a program to address your specific symptoms. The exercises will help you learn to use other sensory inputs to maintain balance, and will likely comprise various head, eye, and body movements. You may be asked to balance on one leg, or on a foam or uneven surface while performing these movements. This allows your brain to correctly interpret the balance 
information from the inner ear, and to reconcile it with the information from your other sensory systems. Practicing controlling your balance by relying on the vestibular system alone will help your body gradually learn to correctly interpret balance signals, reconcile those signals with the other available sensory information, and provide the proper postural balance strategies. By eliminating the sensory conflict, the symptoms of dizziness, disequilibrium, nausea and imbalance can be reduced or eliminated. Research has shown that vestibular rehabilitation can significantly improve function and hasten recovery from a unilateral vestibular loss.
While physical therapy cannot cure a unilateral vestibular loss, treatment eliminates or greatly reduces the symptoms of dizziness while also improving balance, speeding up recovery time, and maximizing function. Vestibular rehabilitation therapy can also teach you to recognize your limits, thereby increasing both your personal safety and your freedom of movement, and maintaining your progress over time.
