What should I consider when fitting a patient with a medically complex SNHL?
Some fitting ideas to keep in mind when dealing with medically complex SNHL include:
- Be careful with the gain. We need to recognize how much threshold loss there is and be sensitive to the fact that we are going to need gain in order to restore some audibility. Due to the significant hearing loss, we are not going to be able to restore as much audibility as we would like to in these patients.
- Role for MCNL. There's probably a significant role for multi-channel nonlinear fitting approaches. Perhaps we need to back off our expectations of how much audibility the patient is going to receive. This is most important for soft to moderate inputs in order to make sure that we're not overdriving their hearing.
- May need to "over-compress" or control dynamics. Normally, most audiologists are very careful about using too much compression. However, when dealing with more complex cases (e.g., Meniere's, progressive HL), we might need to use more fast-acting compression then we are used to because the inner ear may be more sensitive to a highly dynamic signal. This goes against the trend that we're seeing in our field which is to use short-term linear approaches or slow-acting compression. Oftentimes, clinicians use compression approaches that allow the full dynamics of the speech signal to come through. For these patients, there may be situations where it is appropriate to provide more compression than we are typically used to.
- More adaptive than typical losses. Without a doubt, these fittings become more adaptive. We just have to spend time with these patients to try to find which works best for them.
- Environmental control. Due to the amount of distortion that they have in their hearing loss, these patients are thrown by any amount of competition. As such, we need to make sure we're trying to use the very best environmental control (e.g., noise reduction, directionality) that we possibly can in the hearing aids.
I often use the term medically complex sensorineural hearing loss to distinguish it from the more traditional presbycusic/noise-induced loss cases. Another term that can be used is severe distortional sensorineural hearing loss. Almost everyone with SNHL has some degree of distortional element. If that distortional element seems to be more dramatic in some patients, “severe distortional SNHL” is an accurate way of functionally describing what they are facing.
Variability among patients increases with greater degrees of hearing loss. These etiologies typically show a more threshold-based loss, but that is not always the case. In general, increasing degrees of distortional aspects of hearing loss will also increase the variability from patient to patient. We like to follow a prescriptive approach when we fit hearing aids; but when you are dealing with patients with a severe distortional loss, prescriptive approaches might not be successful. There's nothing wrong with starting with prescriptive targets for these patients. But I think it is important to have an attitude that this fitting is going to be more adaptive. Adjustments to the fitting are needed in order to make the best use of the remaining auditory abilities that that patient has. Those remaining abilities vary greatly from patient to patient.
Generally, the greater the damage, the more variable the damage. That is a pretty broad statement, but fairly accurate. When you talk about patients with mild hearing loss, the sort of changes that have occurred in the auditory system (e.g., outer hair cell loss) is pretty easy to predict and manage. However, when you start talking about some of the other changes (e.g., membrane disruptions, neural cell death, mechanical and metabolic disruptions and disrupted coordination), that is where the variability goes up, the damage becomes greater and the complication for doing something to fit the hearing aids becomes greater.