Ultrastructural effects of hypercholesterolemia on the cochlea

Hypothesis: The goals of this study were to identify the effects of hyperch olesterolemia on the cochlea and to rind out where the pathologic changes f irst occur. Background: Some authors have stated that hypercholesterolemia alone does n ot produce auditory dysfunction. Others propose that auditory dysfunction i s caused by glycogen accumulation and other alterations on cochlear ultrast ructure. Methods: Twenty guinea pigs were classified as a control group fed with a n ormal 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 audito ry brainstem responses. The basal and apical turns of the cochleas were exa mined by light microscopy and transmission electron microscopy. Results: The control group showed normal cochlear ultrastructures consisten t with normal hearing thresholds, whereas the cholesterol group had profoun d edema in the strial marginal layer and slight edema in the outer hair cel ls, in line with data from auditory brainstem responses revealing changes i n hearing sensitivity in various degrees. The pathologic changes in the bas al turn and the stria vascularis were qualitatively prominent in comparison with those of the apical turn and the outer hair cell. Conclusions: 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 th e stria vascularis and then spread over the outer hair cells, mainly in the basal turn.