Some first develop hyperacusis in one ear, but in most cases both ears ultimately become affected. Hyperacusis can come on slowly or suddenly. Some patients say they developed hypersensitivity to sound over a period of time. Others may come down with hyperacusis suddenly by attending a rock concert, firing a gun, air bag deployment in their car, fireworks or any extremely loud sound.
Other causes may include job related noise exposure, drugs, Lyme's disease, Meniere's, Temporomandibular Joint Syndrome (TMJ), head injury, Superior Canal Dehiscence Syndrome (SCDS), postoperative surgery, autism or Down Syndrome.
A PUZZLING PROBLEM
The appearance of hyperacusis in some of these disorders may provide clues as to the cause of hyperacusis. Sometimes it disappears once the patient heals from the surgery, Meniere's goes into remission, or TMJ is resolved.
The protective mechanisms a normal ear employs to minimize the harmful effects of loud noise are malfunctioning, so noise may seem too loud even with hearing protection. There is some speculation that the efferent portion of the auditory nerve has been affected - efferent meaning fibers that originate in the brain, which serve to regulate incoming sounds. This theory about hyperacusis suggests that the efferent fibers of the auditory nerve are selectively damaged while the hair cells that allow us to hear pure tones in an audiometric evaluation remain intact. Some have said that it involves a direct malfunction of the facial nerve; as a result, the stapedius muscle is unable to dampen sound.
Since an estimated 10% of all tinnitus patients have no measurable hearing impairment; it comes as no surprise that other ear pathologies including hyperacusis can occur in the absence of hearing loss. Others feel hyperacusis is purely a central processing problem limited to how the brain perceives sound. Hyperacusis is not uncommon. It has been said that 5 million patients have tinnitus and 40% of those patients have hearing sensitivity or hyperacusis. Drug companies in our world today are especially interested in finding drugs that help large groups of people. This is very profitable for them. From that standpoint alone, research is being done to solve tinnitus. Some dominant voices in the world of tinnitus have said that tinnitus and hyperacusis are two sides of the same coin. If a cure is found for one, it is likely that a cure will be found for the other. In the meantime hyperacusis is a mystery but clues are beginning to surface which are very encouraging and hopeful.