Audiologists regularly encounter the following scenario: A patient comes into the clinic with complaints of difficulty hearing speech in background noise. An adult patient is often accompanied by a family member, perhaps a spouse or an older child, who readily confirms his or her loved one's communication problems. Concerns about difficulties with speech perception in noise are often raised by parents of school-age children. The child's school teacher and maybe primary care physician share the concerns. Then, the patient's pure tone audiometry reveals hearing thresholds within normal limits. Or, especially for the elderly, the audiogram documents a modest deficit in hearing thresholds that is not compatible with the patient's complaints.
Based solely on the results of pure tone audiometry and probably a few simple speech recognition tests, the audiologist may confidently tell the patient and indicate in a formal report that “our testing shows that you have normal hearing.” However, in most cases, this statement is inaccurate, misleading, and of no comfort to patients and their families who are convinced that they have a real and serious hearing problem. So here's a more appropriate response: “The results of a simple hearing test were within normal limits. Now we'll conduct a comprehensive evaluation of your hearing, including tests that measure how your ears and your brain process sound.”
Complaints of difficulty with hearing speech in noise are not uncommon in patients with normal audiograms. In a typical audiology clinic population, pure tone audiometry is normal for about five to seven percent of patients with self-perceived hearing difficulties (Int J Audiol. 2011;50:708 http://bit.ly/2gebHRJ). Hearing thresholds within normal limits are found in the majority of children and adults with complaints of speech perception in noise who are referred to an audiology clinic for evaluation of suspected auditory processing disorders (Hall. Pearson Educational, 2014).
Depending on patterns of test findings and clinical history, different labels have been used in referring to patients with complaints of auditory problems but normal audiograms. These labels include obscure auditory dysfunction http://bit.ly/2gehO8E, King-Kopetzky syndrome, auditory processing disorders, and most recently, hidden hearing loss http://bit.ly/2geh2bV (Hall, Pearson Educational, 2014). In the November 2016 issue http://bit.ly/2gedbeT of The Hearing Journal, Dr. Harrison Lin reviewed the mechanisms of and possible medical interventions for hidden hearing loss—a rather specific disorder within a substantially large population of patients with auditory disability but normal pure tone hearing thresholds. The term “hidden hearing loss” refers to those patients with dysfunction affecting the cochlear nerve synapse associated with noise exposure.
Initial findings of “cochlear synaptopathy” in animal experiments have now been confirmed by the exciting results of a clinical study of college-aged adults with a history of noise exposure but have normal audiograms (J Neurosci. 2009;29;14007 http://bit.ly/2geeElv;PLoS One. 2016;11:e0162726 http://bit.ly/2gefP46). Notably, the test battery used to document hidden hearing loss included a brief questionnaire on noise exposure and hearing abilities in various listening environments, clinical procedures, pure tone audiometry for conventional audiometric and high frequencies, word recognition, distortion product otoacoustic emissions, and both auditory brainstem response and electrocochleography recorded with surface electrodes, plus a TIPtrode in the external ear canal.
Further studies are clearly warranted to provide clinically valuable information about the disorder's prevalence, prevention, and management. Audiologists must play a leading role in learning more about the diagnosis of and intervention for hidden hearing loss.