Definition of Hyperacusis
Hyperacusis is an auditory disorder characterized by unusual intolerance to ordinary environmental sounds, where sounds of relatively normal volume are perceived as excessively loud, uncomfortable, or even painfully loud. 1
Core Clinical Features
Reduced sound tolerance is the hallmark feature, where patients experience abnormal reactions to sounds that would be considered normal or comfortable by individuals without the condition 2, 3
Decreased loudness discomfort levels (LDLs) are consistently observed, meaning patients reach their threshold for uncomfortable loudness at lower sound intensities than normal 3, 4
Steeper loudness growth functions occur, where perceived loudness increases more rapidly with increasing sound intensity compared to normal hearing individuals 4
Symptom Categories
Hyperacusis encompasses multiple dimensions of abnormal sound perception that can be grouped into distinct categories 5:
Excessive loudness perception: Sounds are perceived as louder than they objectively are, even at moderate intensity levels 3, 4
Annoyance reactions: Marked distress from sounds that may be unrelated to actual loudness levels 2
Fear responses: Anxiety about potential harm from sounds, which promotes avoidance behaviors and excessive use of ear protection 2
Pain sensations: Physical discomfort or pain associated with sound exposure 2, 5
Associated Conditions
Tinnitus co-occurs in approximately 85% of hyperacusis patients, suggesting potential shared underlying mechanisms 4
The condition is commonly reported in association with neurological conditions (migraine), psychiatric conditions (depression), and otologic diagnoses including noise-induced hearing loss and middle ear dysfunction 2
Bell's palsy patients may experience hyperacusis as one of several auditory symptoms, along with taste disturbance, eye or mouth dryness, and facial weakness 1
Pathophysiologic Understanding
Current evidence suggests increased neuronal response gain in the central auditory system as the primary mechanism, rather than peripheral auditory dysfunction 4
The gain increase appears to be non-linear and applied after subtraction of spontaneous auditory nerve activity, which distinguishes it mechanistically from tinnitus generation 4
This central gain amplification can be either generalized across all frequencies or frequency-specific, particularly affecting high-frequency ranges 4
Clinical Context
The natural course of hyperacusis remains largely unknown, and there is limited high-quality evidence on treatment outcomes 2
The condition can be extremely debilitating, forcing patients to dramatically alter work and social habits in response to increasingly noisy environments 5
No gold standard diagnostic test currently exists, though assessment approaches include questionnaires (Hyperacusis Questionnaire), LDL measurements, and psychoacoustic rating scales using natural sounds 3