Auditory Dysfunction and Multiple Sclerosis: A Silent Concern;

Stephen Fausti, PhD

Hearing lost is the number one service-connected disability of veterans. Approximately 300,000 individuals are service connected and receiving compensation for their hearing losses. However, there are another million or 1.2 million that are service connected less than 10% and are still service-connected for their hearing. Add on the fact that the aging population we're dealing with, and the related statistics tell us that for anybody in the audience over 65, there is a 40% probability that you're going to have some degree of hearing loss.

We've got a problem in the VA with respect to hearing sensitivity and hearing function. If you look at multiple sclerosis and the effects of multiple sclerosis on hearing, and then look at the concomitant effects of the two being additive, we have a potentially big problem.

The National Center in Portland for Rehabilitative Auditory Research has been in existence for about a year and five months. Its basic mission is to alleviate the communicative, social, and economic problems resulting from auditory system impairment. This boils down to financial, social, and a lot of quality-of-life issues that exist in hearing dysfunction.

It's implicit in the charge of the Center to address issues related to auditory dysfunction in veterans with MS. What is surprising is that some studies regarding MS patients have shown auditory information processing deficits that appear to be even larger in magnitude than visual processing deficits. Yet, there have been no large-scale epidemiological studies to look at extent of this problem.

Before discussing the basic problems associated with MS, the differences between peripheral and center types of hearing lost have to be separated out. Hearing per se is a function that is a continuum from periphery to central function. Now it is true that multiple sclerosis basically does not effect the cochlear function. However, it does affect a cochlear function at the connection to the brainstem, and it will affect the auditory pathways of higher levels. Some of the effects of multiple sclerosis can show up as loss in hearing sensitivity. What has been shown in the literature, however, is tremendously contradictory. The only certainly is that there is a problem.

The individuals who treat patients with multiple sclerosis and their hearing loss know that 85% of the cases with hearing loss show a sensory neural bilateral high frequency hearing loss. Sometimes there is unilateral hearing loss, and occasionally there is sudden hearing loss; then in periods of remission, there is some recovery. But there seems to be a sequence where it is progressive and continues to move out with time.

The studies that reported hearing loss basically give us a statistic from 1 to 86%; a huge variation that leaves us with no indication of reality. The only way to know reality is to study reality and to do the prospective study that really looks at degradation of hearing as a result of the disease process. There was similar uncertainty and quite that much variability with the area of ototoxicity and how drugs affect hearing. This continues to be resolved through the process of investigation.

With respect to MS and higher-level auditory dysfunction, it has been reported in the literature that up to 40% of MS patients who have normal audiograms experience difficulty hearing in everyday listening conditions. This is more in keeping with the anecdotal evidence you get from clinicians, when they tell you that hearing loss is really not a problem with my MS patients, but about a third of them complain about having a lot of difficulty hearing with a lot of background noise. There is a big difference between sensitivity and processing of auditory information, which is below the level of auditory memory—what the neuropsychologists are dealing with. There is a need to look at what is going on at the higher levels. In the past a lot of people have used auditory evoke response audiometry, and they've shown that with MS there are dramatic changes. What has been seen with the AVR is that it is a bimodal response. If the eighth auditory nerve is effected, you are going to have marked changes in the AVR.

In addition, longer latencies or evoke potentials measuring higher-level functions also parallel this. In some cases these auditory processing abnormalities have been detected in the very early processes of the disease.

What's needed is a large-scale epidemic study because the literature is so variable on this. Such a study should not only assess the prevalence and severity of auditory processing dysfunctions in individuals, but also should determine the extent to which such dysfunctions may add to the individual's overall disability. In other words, how does it add to existing hearing losses that the individual may have? How does it add to these existing measures of comprehension and auditory retention? The epidemiological study, if it's conducted in the right way, should spin off appropriate screening tasks that are sensitive to utilization and the early detection of these auditory dysfunctions in that population.

What we're not doing much of right now is educating clinicians regarding the subtleness of auditory dysfunctions. We're really not educating the patients because patients come in and tell us that they don't know why they are having trouble hearing noise now; they never did before. Some of that information should be given to the patients up front, and their families also should be brought into the loop.

Secondly, we should be testing patients as soon as we bring them into the program or get them into the following program for MS. At the very least, pure tone audiometry tests can be performed as well as some distorted speech testing to see when they start shifting and if they shift. And thirdly you can implement some degree of rehabilitation with them. If you have a veteran patient who has a peripheral hearing loss, why not upgrade that peripheral hearing loss in the rehabilitative process as well as you can, so you can approve the quality of signal with which he is coping.

Other strategies would include signal noise ratios, is a real dilemma for individuals that speech annoys. There are assisted listening devices like FM units that can be worn. Simple techniques work, like improving your listening environments at home by moving signal sources closer do work. So an active plan of intervention can be formulated. However, most important is early identification, prospective planning, periodic monitoring, and updating. With the increased life expectancy, let's hope medication and pharmacology and immunology come together, and we're able to do away with this disease or we're able to hold it at bay.

In summary, while there are well-documented auditory changes associated with MS, the rehabilitating strategies are really undefined. If you look, it's about, 200 to 1 ratio of publications documenting case studies of auditory dysfunction. There is a need for intervention studies to closely follow epidemiological studies. We need the documentation of change in auditory function in MS patients, and we want to characterize the deficits, which will lead to the needed rehabilitation and remediation strategies.


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