Distortion product otoacoustic emissions in otosclerosis: intraoperative findings

The aim of the study was to investigate changes in middle ear dynamic characteristics caused by both otosclerosis and stapes surgery (platinotomy, prosthesis positioning, ossicular chain maneuver) and to evaluate distortion product otoacoustic emissions (DPOAEs) before and following surgery. The study included 15 patients (12 women, 3 men; mean age 51 years; range 32-69 years) with advanced otosclerosis. All the patients were evaluated with the use of pure-tone audiograms (preoperatively, 5 and 30 days after surgery), stapedial reflexes (preoperatively), and DPOAE recordings (preoperatively, at the end of surgery, and 5 and 30 days after surgery). Changes in the hearing thresholds and in the DPOAE amplitudes were compared. Preoperative tests showed conductive hearing loss, with a mean air-bone gap of 36.6 dB HL ranging from 0.25 to 1 kHz, and no stapedial reflexes were detected. DPOAEs were not measurable preoperatively, and they were detected only in 2 patients at the end of surgery, with low amplitudes in a narrow frequency range. No significant changes occurred in DPOAEs 5 days postoperatively. A month after surgery, improvement in conductive hearing loss was observed; the mean air-bone gap from 0.25 to 1 kHz was 12.9 dB HL, whereas the higher frequencies were still affected by the disease. DPOAEs increased in amplitude in 4 patients, but this was not significant. It remains unclear why DPOAEs are not detected despite a subjective hearing improvement and a sufficiently closed air-bone gap at least in middle and low frequencies. The results of our study show that DPOAEs cannot replace behavioral threshold tests; they may only be included in a battery of tests for a complete clinical follow-up for efficiency monitoring after stapes surgery.