Endolymphatic Deafness: A Particular Variety of Cochlear Disorder

Experimental and clinical data made us consider some types of perceptive hearing loss secondary to an alteration of the secretory structures of the cochlea including stria vascularis, spiral ligament and supporting cells. These structures are responsible for the secretion of endolymph, a fluid characterized by a high potassium concentration (150–180 m<i>M</i>), a low sodium concentration (<1 m<i>M</i>) and a positive potential (80–100 mV). This intracellular-like fluid fills the endolymphatic compartment and is essential in the transduction process which takes place in the organ of Corti. Experimental studies have shown that drugs such as loop diuretics induced marked histological lesions in the stria vascularis and profound alterations in the electrochemical features of endolymph. Histopathological data have demonstrated that several entities such as prebyacusis, sudden deafness, and congenital or acquired progressive hearing loss could be related to strial abnormalities. Recent genetic studies have shown that a mutation of genes encoding connexins, a gap junction protein present in the secretory structures, was involved in some dominant or recessive forms of congenital deafness. Finally, the evaluation of labyrinthine fluids in humans has evidenced a decreased endocochlear potential in two cases of progressive flat hearing loss. All these arguments suggest that among the various types of so-called ‘sensorineural’ deafness, several entities including strial presbyacusis, diuretic-induced ototoxic deafness, some forms of congenital hearing loss and sudden deafness should be classified as endolymphatic deafness. Such an identification seems necessary since these entities result from different pathogenetic mechanisms, do not have the same evolution nor will they probably benefit from the same therapeutic management.