Middle ear mechanics in subjects with rheumatoid arthritis

The incudo-malleolar and incudo-stapedial joints are true diarthroses and therefore may be subject to the same rheumatic lesions as any other articulation in the body. The existence of this involvement in rheumatoid arthritis (RA), however, is highly controversial. The present study investigates modifications of the mechanical properties of the middle ear in a group of subjects with RA by evaluating the resonance frequency obtained with multiple-frequency tympanometry (MFT). Thirty patients with RA, aged 20 to 68 years (mean age: 45.8 +/- 12.4 years), participated in the investigation. Their data were compared with those obtained in a control group of 48 age-matched subjects. Results obtained in both ears were examined in all subjects. The two groups displayed almost equal hearing levels with mean air conduction thresholds ranging from 10 to 22 dB HL. None of the subjects displayed an air-bone gap greater than 5 dB. Normal resonance frequency, calculated at the 95th percentile from the control group, ranged from 900 to 1250 Hz. Twelve rheumatoid arthritis patients (40 per cent) displayed abnormal resonance values. These findings were monolateral in 9 patients and bilateral in 3. Eleven out of 15 ears with abnormal multiple-frequency tympanometry data were characterized by an increase in resonance and 4 by a decrease. A correlation between abnormal resonance values and more aggressive RA was established. The results of this study suggest that rheumatoid arthritis may involve the incudo-malleolar and incudo-stapedial joints, altering the ossicular mechanics in response to static air pressure modifications. This does not impair sound conduction through the middle ear, but might reduce the protective mechanisms of the middle ear towards high static pressures.