Age-related changes in muscle fiber regeneration in the human thyroarytenoid muscle

Background: Muscle fiber regeneration is essential to maintain normal muscl e fiber populations and muscle mass by continuous replacement of fibers los t to acute muscle injury or over use. However, the extent of ongoing muscle fiber regeneration in the laryngeal muscles is unknown. Objective: The present study provides statistically unbiased, quantitative estimates of the content of regenerating fibers in the human thyroarytenoid muscle over the adult lifespan. Design: III the adult, only regenerating muscle fibers express the developm ental myosin isoform. Therefore, regenerating fibers were identified using immunohistochemical techniques. The content of regenerating muscle fibers i n the entire muscle volume was then estimated using stereological technique s. Through the use of a computer-automated sampling protocol, stereological data were collected from sets of isotropic uniform random cryostat section s. Overprojection error was minimized by using a confocal laser-scanning mi croscope to image thin optical sections for use as sample fields. Subjects: Eight autopsy cases, subjects ranging in age from 19 to 81 years. Results: The summed length of fibers expressing developmental myosin increa sed significantly (P=.02) with age when compared with the overall muscle fi ber length. Conclusions: This finding indicates that muscle fibers maintain the capabil ity for spontaneous regeneration, and that the proportion of regenerating f ibers increases as the thyroarytenoid muscle ages. This increase is possibl y a compensatory response to an age-related increase in muscle fiber injury or death.