Middle-latency responses to assess objective thresholds in patients with noise-induced hearing losses and Ménière's disease.

In this study 23 patients with noise-induced hearing loss (NIHL) referred for medico-legal evaluation and a group of 18 cases with Ménière's disease were evaluated audiologically using the middle-latency response (MLR). Cross-correlation functions were used to assess precisely MLR thresholds in low and middle frequencies. Cross-correlation data obtained from suprathreshold levels to below threshold levels were compared with the normal limits of parameters found at threshold levels, allowing us to determine the true MLR threshold. Our results revealed that this MLR threshold and visual detection thresholds were different in 18% of both the NIHL and Ménière's disease groups. In this population the true MLR threshold was greater by 5 dB. These findings demonstrated that cross-correlation functions can enhance the sensitivity of the definition of the MLR threshold. True MLR thresholds were compared with subjective pure-tone audiometric (PTA) thresholds at the same frequencies (0.5, 1 and 2 kHz). The true MLR threshold and PTA threshold were in agreement within 10 dB in 91% of the NIHL group and all of the Ménière's disease group. The PTA threshold was greater by 15 dB or more in the remaining NIHL group. If a criterion of 15 dB discrepancy indicates non-organic hearing loss, it can be inferred that 9% of an NIHL population referred for medico-legal evaluation is exaggerating subjective audiometric thresholds.