Tectorial and basal membranes in experimental hypothyroidism.

The aim of the study was to trace subtle changes in the membranous labyrinth after experimental hypothyroidism that, at least in part, could explain how a reversed hearing impairment can occur, as is often clinically encountered in hypothyroid patients after thyroid substitution therapy. Adult Sprague-Dawley rats were made hypothyroid during six weeks by the use of methimazole in their drinking water. Their inner ears were investigated morphologically at the end of this period. The tectorial membrane is the first structure of the inner ear to show morphologic changes in hypothyroidism. Changes in the normal position and structure constantly were found. A thickening of the basilar membrane was indicated in many, but not all, specimens and in some control animals and may be coincidental. The initial morphologic changes are likely to be reversible after substitution therapy.