[Progressive sensorineural hearing loss: metabolic, hormonal and vascular etiology]

Metabolic, hormonal and vascular disorders are considered to cause hearing dysfunction such as progressive sensorineural hearing loss (PSNHL). The diseases most commonly associated with PSNHL are diabetes mellitus, congenital and acquired hypothyroidism, chronic renal failure, chronic labyrinthine ischemia determined by non-hematologic factors (tissue perfusion pressure, blood vessel diameter) or by hematologic factors (blood viscosity and/or rigidity of the red blood cells). In this study a review of data on the relationship between these clinical disorders and the presence and deterioration of the hearing function was carried out. PSNHL seems to be significantly associated with diabetes mellitus, in particular the mitochondrial type: a progressive deterioration of the hearing function is reported in 60% of the patients suffering from this type of disease with mitochondrial mutations. Regarding hypothyroid disorders, the data do not support a pathogenetic link between PSNHL and acquired hypothyroidism, whereas in subjects with congenital hypothyroidism both clinical and experimental results indicate a progressive damage of hearing function if the thyroid disorder is not treated early in life. Also, in patients with chronic renal failure the hearing thresholds seem to be significantly worse than in control subjects, particularly in patients undergoing dialysis, whereas the effect of kidney transplantation on auditory function is still not understood. Finally a relationship between PSNHL and chronic labyrinthine ischemia due to alterations of hematologic factors (increase of blood viscosity and/or increase of rigidity of the red blood cells) has been reported by several authors. However, data on high blood pressure and hyperlipoproteinemia as causes of deterioration of hearing acuity are controversial, and it is often difficult to understand whether the progressive hearing deficit is due only to these factors or also to the elderly age of patients.