Immediate and delayed cochlear neuropathy after noise exposure in pubescent mice.

Moderate acoustic overexposure in adult rodents is known to cause acute loss of synapses on sensory inner hair cells (IHCs) and delayed degeneration of the auditory nerve, despite the completely reversible temporary threshold shift (TTS) and morphologically intact hair cells. Our objective was to determine whether a cochlear synaptopathy followed by neuropathy occurs after noise exposure in pubescence, and to define neuropathic versus non-neuropathic noise levels for pubescent mice. While exposing 6 week old CBA/CaJ mice to 8-16 kHz bandpass noise for 2 hrs, we defined 97 dB sound pressure level (SPL) as the threshold for this particular type of neuropathic exposure associated with TTS, and 94 dB SPL as the highest non-neuropathic noise level associated with TTS. Exposure to 100 dB SPL caused permanent threshold shift although exposure of 16 week old mice to the same noise is reported to cause only TTS. Amplitude of wave I of the auditory brainstem response, which reflects the summed activity of the cochlear nerve, was complemented by synaptic ribbon counts in IHCs using confocal microscopy, and by stereological counts of peripheral axons and cell bodies of the cochlear nerve from 24 hours to 16 months post exposure. Mice exposed to neuropathic noise demonstrated immediate cochlear synaptopathy by 24 hours post exposure, and delayed neurodegeneration characterized by axonal retraction at 8 months, and spiral ganglion cell loss at 8-16 months post exposure. Although the damage was initially limited to the cochlear base, it progressed to also involve the cochlear apex by 8 months post exposure. Our data demonstrate a fine line between neuropathic and non-neuropathic noise levels associated with TTS in the pubescent cochlea.

Phonosurgery of vocal fold polyps, cysts and nodules is beneficial.

INTRODUCTION: This study reports our experience with microscopic phonosurgery (PS) of benign lesions of the vocal folds. MATERIAL AND METHODS: During the five-year period from 2003 to 2007, a total of 97 patients had PS for vocal fold polyps (n = 63), vocal fold cysts (n = 17), vocal fold nodules (n = 12) or vocal fold oedema (n = 5). Their average age was 41 years; 62% were women and 69% were smokers. Post-operative voice therapy was given to 45 patients. Post-operative clinical evaluation was available for data analysis in 89 patients (92%). Voice quality was assessed using the Multi-Dimensional Voice Program (MDVP), video-stroboscopy and self-reported assessment. The median follow-up time was 3.9 months. RESULTS: Post-operative voice quality was reported as unaffected in 85%, improved but moderately affected in 13%, and severely affected in one patient with a cyst and vocal fold sulcus. Unaffected voice quality was obtained in 91% of patients not receiving voice therapy and in 77% of patients receiving voice therapy. All lesions except one polyp in the anterior commissure were completely removed. MDVP was performed both pre- and post-operatively in 22% of patients. The effect was a significant improvement of jitter (p = 0.013), shimmer (p = 0.001) and Soft Phonation Index (p = 0.013). CONCLUSION: PS is a quick and effective treatment with uncommon and transient post-operative complications. Objective assessment of the voice pre- and post-operatively should be used consistently and applied in controlled studies evaluating the additional impact of pre- and post-operative voice therapy. FUNDING: not relevant. TRIAL REGISTRATION: not relevant.