Experience with a medicolegal decision-making system for occupational hearing loss-related tinnitus

Owing to an increasing number of requests for compensation, a medicolegal decision-making system for tinnitus related to noise-induced hearing loss (NIHL) has been elaborated at the Federal Belgian Institute of Occupational Diseases. Experience with 113 patients, all of them claiming compensation for NIHL and tinnitus, is now available. The patients underwent an exhaustive audiological investigation, and their professional career and noise exposure were carefully and objectively documented. We reviewed the group of 35 "accepted" cases (i.e., with chronic tinnitus recognized as related to NIHL and financially compensated as an occupational disease) and analyzed the medicolegal arguments for acceptance or rejection. In these patients, tinnitus was mostly bilateral, was perceived on average at a frequency of 4 KHz and with a supraliminal intensity of 7.2 dB, and lasted on average for 7.3 years. To gain better insight into the relationship between cochlear damage and chronic tinnitus, we compared our group to a control group of 35 patients with similar hearing thresholds at 3 and 4 KHz but free of tinnitus. The main difference is a significantly steeper slope of the audiometric curve between 2 and 3 KHz in the tinnitus group. Furthermore, a notch in the distortion product-gram is noticed in 60% of the ears affected by tinnitus versus 9% of the ears in the control group. This abrupt discontinuity in the activity along the tonotopic axis of the auditory system-the main characteristic of NIHL-could be a factor eliciting tinnitus, as a correspondence between the audiometric notch and tinnitus frequency appears to exist.