SIR: Dr. Gordon rightly points out that there are many forms of audiological hypersensitivity, differing in clinical presentation and pathophysiology, and there is a need for clear terminology to distinguish them. It was beyond the scope of our paper to go into these entities in detail, and Dr. Gordon offers some helpful clarification. There are, however, some terms that are used differently in our sources1,2 from those Dr. Gordon cites. Most notably, what he terms "hyperacusis" is what we would designate as "hyperacute hearing," and what he calls "audiosensitivity" is what we term "hyperacusis." An additional clinical entity that can mimic or compound hyperacusis is "phonophobia," a cortically determined avoidance of and greater sensitivity to anticipated than unanticipated sounds. Clearly there is a need for standardization in the usage of these terms.
Dr. Gordon is mistaken in stating that we "claimed a central origin for ‘hyperacusis’." We rather hypothesized a central origin for a particular form of hyperacusis observed in some patients with late-stage Lyme disease. This form of hyperacusis, characterized among other things by a kindling-like intensification of sound intolerance in response to subthreshold sound stimulation, is very rare among hyperacusis patients in general and responds poorly to treatments such as Tinnitus Retraining Therapy that appear to be effective for the more common forms of hyperacusis.
Dr. Gordon rightly points out that Lyme disease, like syphilis, can affect the inner ear, causing hearing loss, vertigo, and/or the Tullio phenomenon. Among his arguments in favor of a peripheral origin for Lyme disease—induced hyperacusis is that Lyme disease can cause a clinical syndrome similar to Meniere's disease. Mistakenly, however, he assumes a confluence of symptoms that can occur in Lyme disease but that do not, as in Meniere's disease, typically occur together. Among the protean manifestations of Lyme disease, some symptoms occur more or less independently while others form symptom-clusters suggestive of a common locus of pathology. Although Lyme disease can indeed cause hearing loss, the vast majority of patients who develop hyperacusis due to Lyme disease do not have hearing impairment. Most do, however, experience other sensory hyperacuities (e.g., to light, taste, smell, touch, and vibration) that fluctuate in intensity concomitantly with their hyperacusis. We have observed kindling-like effects not only in the context of hyperacusis alone, but also across sensory modalities. Exposure to bright or flickering light, for instance, is associated (in some patients) with a lowered sound tolerance threshold. It was these phenomena that led us to postulate central involvement in the production of Lyme disease—induced hyperacusis.
Further research into the various kinds of hearing sensitivity and their respective pathogeneses and into the pathogenesis of the neurological and neuropsychiatric effects of Lyme disease is needed in order to determine how and why hyperacusis occurs in Lyme disease and how best to treat it.
We appreciate Dr. Gordon's contribution to the understanding of these phenomena.