Intratympanic Botulinum Toxin Injection as a New Therapeutic Modality for Middle Ear Myoclonic Tinnitus

Abstract

Objective: Middle ear myoclonic tinnitus (MEMT) is a disease caused by myoclonus or abnormal contractive movement of middle ear muscles (MEMs). This translational study was conducted to propose intratympanic botulinum toxin (IT-BTX) injection as a new therapeutic modality to treat MEMT.

Study design: Animal experiment and nonrandomized controlled clinical trial.

Setting: Laboratory and medical center of an academic tertiary medical institution.

Methods: For the animal study, male Sprague-Dawley rats were divided into 4 subgroups according to the sacrificing day after IT-BTX injection. After initial hearing tests, randomly assigned experimental ears were intratympanically injected with 1 unit/100 μL of BTX-A, whereas control ears were injected with normal saline. Changes in the hearing thresholds, morphometry of the cochleae, electron microscopy study, and immunofluorescence analysis of MEMs were evaluated. For the human study, 10 intractable MEMT patients were enrolled. The hearing thresholds and the degree of tinnitus distress were observed for changes after IT-BTX injection. All patients were followed up for 3 months.

Results: As for the animal study, there were no significant changes in hearing thresholds and cochlear morphologies in all 4 subgroups of the rats. Significant MEM degenerations and immuno-detection of cleaved synaptosome-associated protein of 25 kDa (cSNAP-25) indicated the efficacy of IT-BTX. MEMT patients enrolled for the pilot clinical trial showed statistically significant improvement in tinnitus after IT-BTX injection. No major complications were noted.

Conclusion: The new therapeutic modality of IT-BTX injection for the treatment of MEMT seems highly promising with an excellent result.