Histochemical and morphometrical ageing changes in human vocal cord muscles.

A histochemical and morphometrical study of thyroarytenoid and posterior cricoarytenoid human muscles was done in 43 human adults (38 males, 5 females) with ages ranging from 46 to 87 years. Vocal cord muscles were taken from laryngectomy specimens with carcinoma (25) and from autopsies (18), excluding those with neuromuscular diseases. In all cases the studied vocal cords were clinically and histologically normal in appearance. Only 2 patients received radiotherapy or chemotherapy. Posterior cricoarytenoid muscle was studied in 6 patients with larynx cancer. Mean diameter of thyroarytenoid muscle type I fibers (n = 128) was 38.46 microns and for type II 39.68 microns; fiber percentage values (n = 127) were 44.16% for type I and 55.84% for type II. Mean diameter (n = 6) of posterior cricoarytenoid muscle type I fibers was 42.69 microns and of type II 46.56 microns; type I fibers percentage was 66.15% and type II 33.85%. Statistical regression analysis revealed a progressive decrease in thickness of the mucosa and lamina propria in the right vocal cord along the ageing process. A low increase of endomysial tissue with a low decrease in perimysium in both vocal cords was noticed. In thyroarytenoid muscle, a low increase in type I fiber percentage and a decrease in type II fiber percentage were found. Posterior cricoarytenoid muscle showed a significant decrease in type I fiber percentage and diameter, corresponding to the same increase in variables of type II fibers.