Objective: The physiology of the efferent cochlear innervation and the pathophysiology of tinnitus are 2 important but rather obscure chapters of neuro-otology. The possible interference of the medial olivocochlear bundle (MOCB) in the pathophysiology of tinnitus is not only a matter of strong controversy but also a field with possible important clinical and therapeutic implications. The aim of this study was to reveal the differences in study population, design, and methodology that may have attributed the conflicting results in the existing clinical trials.
Data sources: A review of the relevant literature published between January 1990 and June 2013 was conducted via the PubMed database (www.pubmed.org) with the search terms "tinnitus" and "otoacoustic emissions and suppression or efferent."
Study selection: Clinical studies on patients with additional pathologic abnormalities that may implicate the MOCB, such as hyperacousis or auditory neuropathy, were excluded.
Data extraction: The 15 relevant studies were reviewed for critical differences in the recruitment of their study population and control group, as well as their methods of testing and evaluating the results.
Data synthesis: The different methods and study parameters are compared to each other. Factors known to attribute different MOCB responses, possibly responsible for the controversial results, are highlighted.
Conclusion: The remarkable heterogeneity of the existing studies does not allow for safe conclusions. Insufficient knowledge on the physiology of the MOCB reflex seems to preclude the formation of a consensus on the optimal protocol for the evaluation of its function. Further research is definitely needed.