102: How it can malfunction

103: How it can be fixed!

How about destructive treatment?

How about vestibular rehabilitation therapy (VRT)?

John M. Epley, M.D.

Symptoms of vertigo or imbalance are a reflection of a disorder in the so-called "balance system". This system is under the control of the inner ear, but it also involves vision, the body sensors, the eye muscles and the muscles for maintaining upright posture. These sub-systems are connected together by nerve pathways in the brain. The 'operating system' that links and coordinates all of these functions is called the "vestibular system". In order to understand how disorders of the balance system are treated, you must first know how it functions normally, and how it can malfunction.

How it functions

The "balance system" is a reflex system that allows us to maintain awareness of our spatial orientation at all times, and react to it. Without it, we could not walk upright or follow objects with our eyes when we are moving. For purposes of illustration, we will think of the balance system as a "black box", with inputs and outputs.

This system has 3 categories of sensory inputs into our brain to provide spatial orientation cues:

1. Visual: (from the eyes).
2. Vestibular: Two types of sensors in the inner ear.

1. Rotation sensors in the semicircular canals, provide our sense of head turning.
2. Gravity sensors in the otolith organs, provide our sense of which way is straight down, like a plumb line.

3. Somatosensory (body sense): Pressure and muscle sense from the skin and extremities.

The brain interprets these cues to give us an inner sense of orientation. The brain also sends reflex information to the extraocular muscles in order to keep the eyes stabilized with the environment, and to the muscles of the body in order to maintain upright posture. Like breathing, this all happens automatically at a sub-conscious level, but is subject to volitional over-ride.

Thus, when the head is turned 15 degrees to the right, the rotation sensors signal the brain to turn the eyes 15 degrees to the left, unless one decides at that instant to gaze elsewhere. Likewise, if the body begins to tilt to the right, the gravity sensors so inform the brain, which signals the right foot to push down to counteract the tilt. Or, one can over-ride the reflex and let themselves fall.

Central compensation: A significant aspect of the balance system is the brain's ability to "compensate" after the vestibular sensors in the inner ear are injured. One inner ear can be entirely destroyed, and in time the brain will adjust so that the balance system can function amazingly well on the input from the remaining inner ear.

To understand this process, we must consider first how the system works normally. In its resting state, with the subject sitting quietly upright, input from each labyrinthine sensor is exactly counterbalanced by an opposing input from a complementary labyrinthine sensor in the opposite ear. The brain obtains vestibular information by sensing any difference between the two, much like a balance scale compares two weights (a).

For instance, input from the right horizontal semicircular canal (HSC), which increases when the head turns right, counterbalances the input from the left HSC, which increases when the head turn left. Thus, when the head is turned, an increase in input occurs on one side, and a decrease on the other. The cue for movement of the head is transmitted to the brain as a lack of equilibrium between opposing inputs, like the scale registering the difference between weights (b).

So, when one labyrinth becomes permanently damaged (c), as from viral labyrinthitis, the loss of input from that side is interpreted in the brain as a constant rotation or tilt. Acutely, the person may have the sensation of spinning, and the eyes will be turning (nystagmus). With time, the brain compensates for this new state by readjusting the null point at which the system is again at equilibrium when at rest (d). Then the sensation of spinning and the nystagmus cease. This process may take days, weeks and even months.

The sensory mismatch: Another aspect to the balance system is the production of "vegetative symptoms" -- queasiness, nausea, vomiting, etc., -- when the various sensory inputs don't agree with one another.

A prime example of this occurs on a ship in a storm. As a person looks across the room, everything appears upright, but their gravity sensors (in the inner ear) and pressure sensors in their feet are telling them that the room is actually tilted at an angle. This is called a "sensory mismatch", a conflict between one cue and another, in this case between vision and gravity perception. The mismatch tends to throw the brain into a state of confusion, resulting in lightheadedness, nausea and/or vomiting. We call this "sea-sickness", "car-sickness", etc., depending on where it occurs, but the basic cause is the same.

A sensory mismatch also occurs in certain inner ear disorders, producing the same symptoms. For example, in Meniere's disease, fluid pressure in the inner ear can give a false cue to the brain that the body (or the room) is spinning, but vision and the pressure on the feet indicate otherwise. The resulting nausea is similar to being sea-sick.

In Benign paroxysmal positional vertigo (BPPV), abnormal particles in a semicircular canal cause currents when the head is tilted, creating a false cue of spinning. This can result in a loss of balance because of disorientation, and nausea because of the sensory mismatch.

The irritable focus: (Ed. Note: This is the author's concept.) In other conditions, such as chronic post-traumatic dizziness, an "irritable focus" is created when damaged gravity sensors in an otolith organ become abnormally responsive to rapid internal pressure changes (as from physical activity) and to sound. This abnormal stimulus produces an altered perception of gravity. Because this focus is being constantly irritated, there is a constantly changing misperception regarding gravity orientation, and thus a constant sensory mismatch. And, because this change is occurring so rapidly, the brain is unable to compensate. The effect can be devastating.

In the presence of this virtually constant vestibular irritation, the brain must learn to ignore it and to depend largely upon visual cues for balance control. But, when a person is thus visually dependent, any interference with stable visual cues, as by darkness, a visualized moving object or a patterned background, can cause disorientation and loss of stability. Also, the sensory overload causes difficulty in concentration and mental tasks. This accounts for the typical post-traumatic syndrome of chronic imbalance, nausea, and problems with short-term memory.

Dizziness of central origin: Although most dizziness originates in the ear, it can occasionally be caused by other conditions, such as those affecting the nerve pathways from the labyrinthine sensors. Examples are tumors (acoustic neuroma) and viral lesions (vestibular neuronitis) involving the vestibular nerve, which serves the labyrinth. Vertigo originating more centrally in the brain is usually accompanied by other signs, such as localized numbness or muscle weakness.

Most dizziness, then, is caused by a malfunction that affects the sensors in the labyrinth (semicircular canals or otolith organs). Thus, correcting the problem should ideally involve correcting the malfunction in the labyrinth. In Meniere's disease, the increased inner ear fluid (endolymph) pressure can be corrected. In BPPV, the offending loose particles can be moved out of the semicircular canal with the Epley maneuvers. In post-traumatic dizziness, the sound and pressure sensitive otolith organ can be corrected or desensitized.

(Ed. Note): Unfortunately, most dizziness doesn't get handled this way. One reason is that it takes much time and expense. Most often, medication is given that 'numbs' the balance system. The trouble is, this also numbs the brain, which might be appropriate for a short-term attack of vertigo, but is usually a poor long-term solution. For a numbed brain will be slow to compensate. Further, such "symptomatic" treatment often results in delay in obtaining definitive treatment, thereby incurring permanent damage to the balance system or hearing.

The proper approach is to have a work up with history, examination and testing so as to identify the malfunction, and then to receive definitive treatment directed toward correcting that malfunction.

Meniere's disease, BPPV and post-traumatic vertigo are usually controllable with definitive treatment. So are most other disorders causing vertigo or imbalance. Thus, the need for comprehensive assessment of multiple systems.

The destruction (ablation) concept was based on the fact that if one labyrinth is destroyed, the person will be able to function quite well in time with the other labyrinth alone, after the brain has compensated for the loss. So, if the input from one ear is unstable, as from frequent Meniere's disease attacks, it can be destroyed surgically or chemically, ridding the patient of the attacks. The downside, besides the long period of rehabilitation, is that frequently the disease later occurs in the other ear. Also, one labyrinth is actually never as good as two.

Definitive treatment ideally involves eliminating the cause, not the whole labyrinth.

VRT is mainly made up of exercises designed to restore the normal utilization of the 3 sensory inputs, and most of this involves getting one back in touch with one's vestibular system. VRT can also be helpful in speeding central compensation after permanent damage has occurred to the vestibular sensors, as from acute labyrinthitis.

Definitive treatment ideally involves eliminating the cause, not the whole labyrinth.

But VRT can be effective only when the malfunction is stable and not fluctuating. Thus, it will have minimal effectiveness with any condition that involves attacks of vertigo, whether spontaneous as in Meniere’s disease, or aggravated by such things as position change (BPPV) or sound (post-traumatic dizziness). In fact, when VRT is used with post-traumatic dizziness, for instance, it may make things worse.

VRT can be particularly useful when it is uses definitive treatment, such as the canalith repositioning procedure (Epley Maneuvers) for BPPV.

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