Carhart notch effect in otosclerotic ears measured by electric bone-conduction audiometry

The Carhart notch is an elevation in the middle-frequency bone-conduction threshold of an ear with clinical otosclerosis. The study population consisted of 138 patients with clinical otosclerosis. Conventional air-conduction (AC) and bone-conduction (BC) and electric bone-conduction (EBC, with Audimax 500 audiometer) thresholds were measured 2 weeks before and 7 months after stapes surgery. The EBC thresholds were converted from mA values to dB SPL to compare the results obtained with the different methods. The mean differences in the BC thresholds before and after the operation were 3.2 dB (95% CI 1.9-4.6) at 1 kHz and 7.6 dB (95% CI 6.1-9.1) at 2 kHz. The mean differences in the EBC thresholds were 5.4 dB (95% CI 3.8-6.9) at 1 kHz and 5.3 dB (95% CI 3.4-7.1) at 2 kHz. Thus, both methods showed a distinct Carhart notch effect.