Ultrastructural effects of hypercholesterolemia on the cochlea

The goals of this study were to identify the effects of hypercholesterolemia on the cochlea and to find out where the pathologic changes first occur.

Some authors have stated that hypercholesterolemia alone does not produce auditory dysfunction. Others propose that auditory dysfunction is caused by glycogen accumulation and other alterations on cochlear ultrastructure.

Twenty guinea pigs were classified as a control group fed with a normal diet, and a cholesterol group of 24 animals was given a diet composed of 1 g cholesterol per day for 4 months. The hearing acuity of the animals before the diets was compared with that after the diets by means of auditory brainstem responses. The basal and apical turns of the cochleas were examined by light microscopy and transmission electron microscopy.

The control group showed normal cochlear ultrastructures consistent with normal hearing thresholds, whereas the cholesterol group had profound edema in the strial marginal layer and slight edema in the outer hair cells, in line with data from auditory brainstem responses revealing changes in hearing sensitivity in various degrees. The pathologic changes in the basal turn and the stria vascularis were qualitatively prominent in comparison with those of the apical turn and the outer hair cell.

These observations confirm that hypercholesterolemia alone may cause auditory dysfunction if dietary cholesterol is kept at a high level for a long time. Alterations attributed to hypercholesterolemia begin in the stria vascularis and then spread over the outer hair cells, mainly in the basal turn.