Timothy C. Hain, MD Page last modified: December 22, 2013
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Bilateral vestibulopathy occurs when the balance portions of both inner ears are damaged. The symptoms typically include imbalance and visual disturbance. The imbalance is worse in the dark, or in situations where footing is uncertain. Spinning vertigo is unusual. The visual symptoms, called "oscillopsia", only occur when the head is moving (J.C., 1952).
The illustration above shows what a person with bilateral vestibulopathy may see when driving over a bumpy road. A movie showing oscillopsia, from one of our educational DVD's, can be seen by clicking here. Oscillopsia often occurs during walking (Freyss et al, 1988). Quick movements of the head are associated with transient visual blurring.
About 1% of all dizziness in the author's practice is due to bilateral vestibulopathy. Click here for a more detailed discussion. In many instances, bilateral vestibulopathy is due to exposure to an ototoxic medication (about 50%). Gentamicin is an antibiotic medication and gentamicin toxicity is the most common single known cause of bilateral vestibulopathy, accounting for 15-50% of all cases. Other antibiotic ototoxins are tobramycin and vancomycin.
Bilateral vestibulopathy can also be due to infection (meningitis, about 10%), Meniere's disease, sarcoidosis, bilateral ear surgery such as for certain forms of acoustic neuroma or bilateral vestibular neuritis, congenital disorders with deafness such as the Mondini malformation, and very rarely, from disorders of the immune system. One rare familial form is associated with migraine. Some causes accompanied by hearing loss may be due to auditory neuropathy. Advanced age is another risk factor as normally vestibular ganglion cell counts decrease with age so that by the age of 80 years, about 50% of vestibular neurons remain. In about a third of all cases no cause can be identified for bilateral vestibular loss (Syms and House, 1997).
There is also accumulating evidence that free radical generation plays an important role in ototoxicity. This information is the basis of experimental treatments to prevent ototoxicity.
A physician can make the diagnosis based on history, findings on physical examination, and the results of vestibular tests (ENG and rotatory chair) .
On physical examination, the tandem Romberg test, the dynamic visual acuity test, and the ophthalmoscope tests are the three most helpful confirmatory tests. The ophthalmoscope test is particularly important as it is straightforward to perform and the results are not greatly affected by cooperation or lack of it. The horizontal head impulse test is favored by some authors (e.g. Weber et al, 2009)
The cervico-ocular reflex is easy to check with a swivel chair and video-frenzel goggles, but it is variably increased. It is inconsistent and not a reliable sign (Schubert et al, 2004). We only do this test in severe bilaterals, and are not sure of its sensitivity ourselves.
Visual suppression is the process of attempting to keep the eyes on a target moving with the person, while their head is being rotated. Visual suppression testing can be useful in detecting patients who are pretending to have gentamicin otoxicity in a hope of being compensated. The idea here is that bilateral patients have a much easier time than normal patients doing suppression, as they have nothing to suppress. Patients who are pretending to have bilateral loss, sometimes are unable to stop their eyes from jumping while suppressing and rotating. We think the best way to do this is with the rotatory chair.
|Rotatory Chair||ENG caloric responses|
|Mild||Increased phase, steeper than normal slope to gain vs. frequency plot.||Normal and symmetric. Total response >= 27 when done with water.|
|Moderate||Increased phase, steep slope of gain vs frequency plot, gain greater than 0.2 at highest frequencies||Total response between 0 and 27|
|Severe||No response at all frequencies except (possibly) highest (0.64 Hz), gain less than 0.4 at 0.64 hz||No response to ice water irrigations|
(These categories are based on testing done at the author's clinic, and might not be applicable to other protocols at other institutions). Pathologic correlation is minimal for these categories -- but recent data suggests that "severe" losses are associated with roughly an 80% or more loss of hair cells. The "mild" bilateral loss pattern resembles that which occurs when one ear is not working (i.e. 50% loss).
Note that the rotatory chair test is generally needed to categorize bilateral patients. Caloric testing by itself is not sufficient, as because of the high variability of caloric tests, even absent caloric responses are sometimes encountered in otherwise normal individuals (Furman and Kamerer, 1989). Although recent authors suggest that a limit of 27 deg/sec is sufficient (Zapala et al, 2008), in our opinion, this limit is not generally applicable because of the wide variation in how testing is performed, and because of the intrinisic variability of ENG responses.
|ENG test. Contemporary ENG methodology uses video-ENG, caloric irrigation, and computer control . See here for more details.||Absent caloric Responses. A total response of less than 20 is abnormally low.|
|Rotatory chair test with optokinetic stimulus superimposed upon its walls. The rotatory chair test is the gold standard for diagnosing bilateral vestibular loss.||Abnormal rotatory chair test in person with bilateral vestibular loss. There is decreased gain at low frequencies and increased phase at all frequencies. The uppermost gain point is in the normal (blue) range.|
The rotatory chair test is useful to document the characteristic reduced responses to motion of both ears and also in assessing compensation and the partial recovery that nearly always occurs over time. Rotatory chair testing generally improves with time -- high frequency gain eventually becomes normal or nearly so, several years after exposure. Recovery at high frequencies is felt to be related to non-vestibular sensory input, and does not necessarily correlate with severity of vestibular injury. Low frequency responses (e.g. < .04 Hz) may remain depressed. Optokinetic afternystagmus is abolished in significant bilateral vestibular loss (Hain and Zee, 1991).
The Vestibular Autorotation Test (VAT) is a variant rotational test where the subject moves their head themselves instead of being rotated by a motorized chair. Another brand name is the Vorteq test. VAT testing is probably less sensitive to bilateral loss than is ordinary rotatory chair testing because of a tendency for high-frequency VOR gain to recover via non-vestibular mechanisms. There has also been substantial Medicare fraud using the VAT test in certain settings.
VEMP testing is nearly always reduced in bilateral vestibular loss, and the combination of absent VEMP's and absent calorics is probably nearly as good as rotatory chair testing for diagnosis of bilateral vestibular loss, given that technique is good. VEMPs are also reduced in older persons, and their utility diminishes after the age of 60.
Moving platform posturography is always abnormal, but it is not specific (i.e. many other disorders also impair posturography). Allum and others recently concluded that diagnosis of bilateral vestibular loss using posturography is best achieved using measure of trunk control following pure toe-up rotational perturbations under eyes-closed conditions (Allum et al, 2001). This is not a paradigm that is routinely available.
Based on rotatory chair testing in our laboratory, patients are divided into three groups: mild, moderate, and severe (see table above). These categories have prognostic significance (see later).
Other diagnostic studies may be helpful. Hearing testing (audiogram) is necessary. ABR testing and otoacoustic emmissions (OAE) may be reasonable in persons with hearing impairment to look for auditory neuropathy. OAE's should be impaired in persons with aminoglycoside toxicity. VEMP testing is useful in detecting otolith function.
A test for syphilis (FTA), and an antibody test (ANA) for autoimmune inner ear disease may be performed. A chest X-ray and ACE test may be done if sarcoid is thought likely, and a Lyme titer may be obtained if there has been exposure (a tick bite in an endemic area).
A research method - -the "HIT" test, can be used to detect bilateral loss associated with gentamicin ototoxicity (Weber et al, 2009). While effective, it is not a practical test for clinical use because it requires a contact lens method of registering eye position. There are also much easier ways (i.e. ENG, rotatory chair, VEMP) to diagnose bilateral loss.
Treatment involves finding out the cause and treating it, if possible. If the damage has already been done, then the focus of treatment is upon avoidance of vestibular suppressants and ototoxins (see following), and vestibular rehabilitation (Krebs 1991; Herdman 2007) are important to speed recovery and prevent setbacks.
There are a number of sensory substitution devices in development. None of these are presently practical. A full discussion can be found here.
In the future, we expect that treatment will be available to regrow inner ear hair cells. This is not possible yet (as of April, 2009), and we do not expect this to be in human trials until roughly 2020.
We recommend that you tell health care workers that you are can't take drugs that end in "mycin", because of possible "reaction". This will keep you from contact with the most common ototoxins. Aspirin and nonsteroidal anti-inflammatory drugs can affect hearing. It may be prudent to avoid these drugs, or at least large doses of them. Antihistamines (like Antivert (meclizine) or Dramamine) and benzodiazepines (Valium-like drugs like Klonopin, Xanax, and Ativan) are temporary vestibular suppressants. While they won't permanently harm you, typically they make imbalance temporarily worse. A list of the most common problem medication follows:
Agents that can cause temporary worsening of dizziness or hearing symptoms are generally vestibular suppressants.
- Antihistamines such as meclizine (Antivert), Dramamine and phenergan.
- Antidepressants such as amitriptyline, especially tricyclic type antidepressants.
- Aspirin or NSAIDS (drugs like ibuprofen and naproxen) in large doses
- Diazepam (Valium), alprazolam (Xanax), lorazepam (Ativan), klonazepam (Klonopin) and related drugs in the benzodiazepine family.
- Verapamil and other calcium channel blockers
In general, any drug that is commonly used to make vertigo better, will likely make the symptoms of bilateral loss worse.
Agents that can cause permanent or temporary worsening of dizziness or hearing
- Cis-Platinum (a chemotherapy drug) and other platinum based drugs.
- Gentamicin and other "mycin" antibiotics, including large doses of erythromycin (although this is actually in a different group than Gentamicin)
- Furosemide (Lasix) and ethacrynic acid (Edecrin) loop diuretics
- Quinine and related drugs (they usually have a "quin" in their name).
These medications need not be avoided at all costs but reasonable judgment should be exercised. Medications that cause only temporary unsteadiness (i.e. meclizine), may still be useful in some situations. Medications that are ototoxic (such as gentamicin), may still be useful in cases of bilateral vestibular loss when there is no reasonable alternative or when the damage done is already so extensive that there is nothing more to lose. Certain bacteria, such as methacillin-resistant staphylococcus aureus (MRSA) are so difficult to treat that ototoxic medications may be required to save a persons life. Nevertheless, as medicine progresses, we expect that newer drugs such as Linezolid will provide reasonable alternatives.
This is a condition which often causes some permanent impairment and disability. In patients with gentamicin induced ototoxicity, the symptoms generally peak at 3 months from the last dose of gentamicin. In the long run however, (2-5 years), most patients are substantially better. In the authors opinion, after 2 years, a small amount of improvement (10%) may still be possible. After 4 or 5 years, it is unlikely that any further improvement will occur.
Mechanisms for recovery: There are multiple reasons why people get better.
- Regeneration: First, there is limited evidence that the damaged vestibular hair cells in the inner ear can regenerate, although the extent to which this occurs and the degree to which they are functional is not presently clear (Forge et al, 1993; Warchol et al, 1993). Birds and reptiles seem to regenerate much better than do humans (Cotanche and Lee, 1994; Forge et al, 1993). At the present writing, most experts feel that regeneration does not account for any substantial amount of recovery.
- Marginal cell recovery: Some recovery presumably occurs because marginal hair cells recover. If this occurs, it probably happens only in the first year.
- Plasticity: The brain can rewire itself to adapt to the new situation. This is a mechanism that probably occurs in all people, although with more effect and speed in younger persons. Behavioral adaptation, Another way to get accomdate to the new situation is for a person to change they way they do things. For example, if one is unsafe driving at night, then don't drive at night.
- Substitution: Recent experimental work suggests that high frequency vestibular-ocular responses to rotation recover via a pathway that does not require vestibular input (Wiest et al, 2001). Thus in time, oscillopsia should improve no matter how severe the vestibular deficit. According to Herdman et al (2007), recovery of visual acuity occurs in roughly 5 weeks. Practically, performance on the "dynamic illegible 'E' test" seems to recover substantially in all patients after 2 or more years, although in persons with severe bilateral loss, return to completely normal is very unlikely.
One can predict prognosis based on the amount of damage done initially, modified by other factors such as age, and other medical problems. Gillespie and Minor (1999) reported that recovery is related to various factors, including of course, severity of lesion. Impairment of other senses used for balance (such as vision or sensation from the feet) is associated with worsened balance and worsened prognosis.
In our experience, rotatory chair testing done at 6 months following onset (preferably later) helps to establish prognosis by dividing individuals into three categories (see table above). One should wait to do this testing till at least 6 months have passed, at least in persons with aminoglycoside ototoxicity (gentamicin mainly), as vestibular loss can progress for months even after gentamicin is stopped. When using rotatory chair testing to attempt to establish long term prognosis, another test at about 2 years or later is recommended as recent data suggests that partially injured hair cells may recover in the interim. These comments are not absolute and there are occasional exceptions where people are seen who do better or worse than would be expected from their rotatory chair tests.
- Individuals with "mild" abnormalities on rotatory testing, are nearly always subjectively normal at one year.
- Individuals with moderate vestibular loss are usually able to continue to work productively, with some modifications in their behavior. For example, most people with moderate or severe loss never return to driving at night. In situations where there is complete or near-complete loss of vestibular function, vision and balance usually remain impaired permanently, but nevertheless, most individuals do return to work, especially if their job does not require good head/eye coordination or balance. Frequently job modification or accommodation occurs.
- Individuals with severe vestibular loss may still return to work, but again the job generally must not require good balance. Because persons with severe bilateral loss often never return to night driving, this must be considered when returning to work.
While balance is poorer than normal (Fujimoto et al, 2013), given that normal vision and sensation in the feet and ankles is present, most patients with bilateral loss appear, at least on casual inspection, to have normal gait. Falls are more frequent in persons with bilateral vestibulopathy (Herdman et al, 2000). Reading is generally more difficult than for persons with normal vestibular systems, but quite feasible, as the head can be steadied during reading.
While crutches, canes, walkers and wheelchairs may be necessary in the first 3-6 months, appliances are rarely needed to get about by one year. The exception to this general rule are patients with severe loss, who also have other medical problems such as neuropathy or brain damage. After 2 years, many patients also have substantial improvement in their rotatory chair tests compared to those done at 3 months, attributed to a combination of adaptation (substitutino), plasticity, and recovery of hair cells that were damaged but not killed.
After 20 years, most patients are functionally nearly normal for their age. Of course, "most" is not the same as "all", and there is substantial variability in outcome. To some extent this return to "normal" is related to aging of peers as normally vestibular function declines with age, and bilateral vestibular loss most often is diagnosed in persons in their 50's through 70's. Other aspects of recovery involve use of other senses such as neck position sensors (the COR or cervico-ocular reflex), vision, and compensation through prediction. (Schubert et al, 2004)
A change in life style may be needed adjust to reduced balance, and inability to see when the head is in motion. You will want to take precautions to avoid falls. Symptoms are generally the worst in the first 6 months and get better from then on out. You will not be likely to need to use a wheelchair for your bilateral vestibular loss, or even a walker after two years, unless there is something wrong with you other than bilateral vestibular loss.
You may need to change your occupation if your present one requires good balance, and an ability to see while the head is in motion. For example, it would not be safe to continue as a truck driver, construction worker, or a roofer if you developed a significant bilateral vestibulopathy. A job where you work at a desk is usually a good choice. Adding night-lights and grab-bars is often helpful in the home. It is safer to live in a house where it is not necessary to climb stairs regularly. Uncarpeted basement stairs can be extremely dangerous. If you drive, it is safer to do it during daylight hours.
While it should be ok to walk and chew gum at the same time, it is not such a good idea to carry on a conversation while you are driving (this is multitasking).
Many people with bilateral vestibulopathy complain of a mild confusion or "brain fog", which is attributed to the increased attention needed to maintain balance and good vision, due to loss of vestibular input. Others call it "inability to multi-task". It is thought that in persons with bilateral vestibular loss, the ongoing extra effort needed to keep ones balance reduces the amount of attention that is available for other thinking tasks. Considerable evidence for this can be found in the recent literature (Andersson et al, 2003; Pellecchia, 2003; Redfern et al, 2003). Persons with other vestibular disorders often complain of difficulty concentrating and mental fatigue (Yardley et al. 1998). Of course, symptoms scale with deficit, with severe bilateral loss patients having more substantial problems.
Considerable research is ongoing regarding bilateral vestibular loss.
Presently efforts are ongoing to develop a vestibular prosthesis (Wall et al, 2001; Rubinstein and Della Santina et al, 2002) as well as other projects involving sensory substitution. See this page for more information about substitution devices.
Another class of research involves mechanisms to stimulate regeneration of hair cells within the inner ear. We think that the regeneration projects are more likely to succeed than the prosthesis project, but we think that support of both of these is highly warranted.
Methods of preventing loss through protective agents and predicting susceptibility to gentamicin through genetic testing are also currently hot topics.
Help with research efforts is much needed to speed progress in this disorder. You may wish to volunteer to be a research subject, to contribute funds for research efforts aimed at treating or preventing ototoxicity, or to contribute your inner ear in the event of your death. Donations of the inner ear of individuals with gentamicin toxicity are sorely needed by the National Temporal Bone bank as no usable specimens existed in the collection as of 1999 (Tsuji et al, 1999).
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