Age-related changes in human thyroarytenoid muscles: a histological and histochemical study.

We examined the thyroarytenoid muscles of 23 larynges in order to assess function-related characteristics and to discover age-related changes. The neonatal thyroarytenoid muscle differed from limb muscles in the slow maturation of fibre types. In adults, we examined the medial part of the thyroarytenoid muscle. It showed a larger variation in fibre size and more endomysial connective tissue than is common for limb muscles. Structural and histochemical evidence of ageing developed from approximately the 6th decade. It comprised a marked increase of endomysial connective tissue and striking myopathic changes of muscle fibres. Up to 20% of the muscle fibres showed at some places of some sections evidence of mitochondrial accumulations and increased mitochondrial enzyme activity (ragged red fibres). The rise of such ragged red fibres is commonly related to the development of mutations in mitochondrial DNA. Significant myopathic changes including mitochondrial abnormalities develop in the thyrovocalis muscle with age and may play a role in the functional deficit of the larynx in old age.