SHORT REVIEW Kidney Disease and Inner Ear Sufferance of Non-Familial Origin: A Review of the Literature and a Proposal of Explanation

Hearing loss and chronic kidney disease (CKD) are frequently associated, and this association has been known since 1927 when Alport described a case of familial kidney disease with concomitant hearing loss . Over the years, a series of observations concerning infrequent affections or syndromes with a close relationship between hearing impairment and CKD was reported : even if the ever more detailed specific knowledge evidenced a shared basis for possible dysfunctions derived from genetic anomalies [3,4], a number of clinical studies about the frequent incidence of hearing impairment in patients with CKD was reported independently of hereditary ascertained disorders. An interesting aspect is represented by the cochlear involvement documented by the alteration of evoked otoacoustic emissions : this is not surprising, as the physiologic, ultrastructural and antigenic analogies between the kidney and the cochlea [2] permit to infer that the link between inner ear damage and kidney failure is likely to be much more than a coincidental finding. Actually, it is well known that the function of both organs is characterized by complex processes of water and ion regulation, that are maintained by the work of different proton pump systems and aim at a homeostasis of ions and pH. The similarities of labyrinthine and renal function are well exemplified by the shared essential importance of aquaporins , specific cellular water channels, and by the presence of an ion transport system that to date has been demonstrated only in the rat and in the human endolymphatic sac beside the kidney . From this point of view, the possible explanation for the association between inner ear and kidney affections by an alteration of the mechanisms involving fluid and