Study of functionality of cochlear outer hair cells in patients with retinitis pigmentosa

Hearing functionality was studied in 30 patients affected by retinitis pigmentosa (RP) and 25 of their relatives. These patients were defined as normal-hearing on the basis of pure-tone threshold audiometric and acoustic immittance tests. The evoked otoacoustic emissions (EOEs) were studied in these normal hearing patients. EOEs are an extremely sensitive method to study the functionality of the outer hair cells of the organ of Corti. In RP patients and in their relatives the values of EOE (amplitude, intensity and frequency) were found to be statistically reduced compared to those of control subjects. The EOEs turned out to be clearly pathological in 60% of patients with RP and in 24% of their relatives. During the embryologic development there is one transitory axoneme in the outer hair cells of the organ of Corti. This axoneme is important for the organization of the stereocilia. The axonemes are found inside a few mature hair cells, including the photoreceptors. The alteration of cochlear outer hair cells in a high percentage of patients with RP and in some of their relatives seems to corroborate the hypothesis that, in many cases, retinitis pigmentosa may be due to a structural anomaly of the ciliated cells.