Progressive hearing loss after single exposure to acute acoustic trauma.

Progressive hearing loss after single episodes of acute acoustic trauma (Knalltrauma) has been reported in only a few cases. Many authors dispute such a progressive evolution. Since this question is of obvious importance in cases evolving into lawsuits, its occurrence also arouses scientific interest. The present study reports 58 bilateral and 17 unilateral cases of acute acoustic trauma showing progression of more than 20 dB at least at one frequency. The mean follow-up time was more than 20 years. The incidence was estimated as less than 1% of cases involving acute acoustic trauma. The evolution of the progressive hearing loss did not show a specific pattern; in the unilateral group, there were no statistically significant differences between the progression in both ears. The findings clearly indicate that late progression of hearing loss due to single episodes of acute acoustic trauma does not exist unless the affected ear is exposed to additional damage not related to the initial trauma.