Pathology of Tinnitus and Hyperacusis-Clinical Implications

Not long ago, tinnitus and hyperacusis were considered intractable symptoms and the lack of interest and shortage of research in diseases with these symptoms would have made publishing a special issue on tinnitus and hyperacusis nearly impossible. During the past two decades, there has been an explosion of research on tinnitus and incremental growth on hyperacusis, a condition associated with hearing loss, autism, migraine, closed head injuries, Williams syndrome, fibromyalgia, and other sensory hypersensitivity disorders. Prior to 1980, a search of PubMed turned up fewer than 25 publications with tinnitus in the title (Figure 1); the situation for hyperacusis was even more dismal with less than 5 publications in 1980 and only 19 in 2014. This increase in publications reflects a large increase in research made possible by new hypotheses about the pathology of these diseases, advances in neuroscience in general, and new technological approaches. The increase in research funding by private philanthropic organizations such as the American Tinnitus Association, the Tinnitus Research Consortium, the Tinnitus Research Initiative, and Action on Hearing Loss has been essential for the progress in understanding of tinnitus and hyperacusis and the treatment of these disorders. Research grants from governmental agencies have also contributed to these advances in research regarding tinnitus and hyperacusis. The incentive for this special issue was the tremendous personal, social, and financial costs associated with tinnitus and hyperacusis. For those suffering from severe or debilitating tinnitus or hyperacusis, the psychosocial and emotional costs can be enormous. While tinnitus and hyperacusis can affect anyone, young or old, those serving in the military are at a higher risk than nonmilitary people. Roughly 50% of combat personnel in the Gulf War developed tinnitus where exposure to intense noise and stress were likely the major contributing factors. Tinnitus ranks as the #1 serviceconnected disabilities in the Veterans Health Care System with compensation costs $1.2 billion for the year 2012, projected to reach $3 billion for the year 2017. The completion of this special issue is a testament to the tremendous efforts by research groups around the world to develop a better understanding of the neural mechanisms underlying tinnitus and hyperacusis and to develop better and more effective therapies. This special issue combines association studies (tinnitus and sleep, tinnitus and headaches, tinnitus and interoceptive awareness, mastoid pneumatization, and pulsatile tinnitus), diagnostic studies (how to measure hyperacusis, the relevance of highfrequency hearing loss in tinnitus), and treatment studies (coordinated reset acoustic stimulation, repeated rTMS sessions). A few highlights from the accepted papers in this special issue are discussed below.