Hidden hearing loss: Cochlear synaptopathy

Abstract

Introduction/Objective: Cochlear synaptopathy, also known in the literature as "hidden hearing loss", represents a primary loss of synapses between inner hair cells and cochlear nerve fibers, while the sensory cells themselves remain preserved. The main etiological factors include noise exposure, aging, and ototoxic drug use. This review aims to provide a comprehensive analysis of the pathophysiological mechanisms of cochlear synaptopathy and evaluate current diagnostic approaches for detecting hidden hearing loss. Methods: This review paper analyzes relevant literature and scientific papers indexed in the PubMed and SCIndex databases. The search included studies on the anatomical and pathophysiological mechanisms of impairment, as well as the validation of new clinical and electrophysiological protocols for identifying synaptic dysfunction. Results: The clinical presentation is characterized by a preserved hearing threshold on standard pure-tone audiometry in quiet, but with a pronounced deficit in speech understanding in noisy environments, accompanied by tinnitus and hyperacusis. Since conventional tests do not detect this impairment, diagnosis relies on advanced electrophysiological methods, primarily the amplitude analysis of wave I of auditory brainstem responses (ABR), as well as psychoacoustic speech-in-noise tests. Current therapeutic options include hearing AIDS with advanced noise-reduction algorithms and audiological rehabilitation, while contemporary preclinical research focuses on neurotrophic regeneration of synaptic connections. Conclusion: The conventional audiological approach is insufficient for detecting cochlear synaptopathy; therefore, it is essential to introduce advanced electrophysiological and psychoacoustic tests into clinical practice. Timely understanding of this entity is crucial for early identification and prevention of permanent auditory dysfunctions.