Skeletal Muscle - Atrophy

comment:
Skeletal muscle atrophy can occur due to degenerative processes originating within the skeletal muscle fibers, secondary to denervation (denervation atrophy), or spontaneously in aging rodents. It is a common reaction to any injury that results in the degradation and/or loss of myofiber organelles. Examples include disuse, cachexia, nutritional or metabolic derangements, vascular insufficiency, disturbances of hormonal growth control mechanisms, and administration of myotoxic xenobiotics. Compensatory hypertrophy of surviving/unaffected myofibers is often present concomitantly, regardless of the cause.The main histologic feature of skeletal muscle atrophy is a reduction in myofiber diameter ( Figure 1


Atrophy can uniformly affect myofibers or selectively target specific muscle fiber types. Type II fibers are selectively affected when atrophy is associated with disuse, cachexia, or malnutrition. Chronic administration of corticosteroids in rats results in the selective atrophy of type II fast-twitch fibers. Conversely, type I fibers are selectively targeted during experimentally induced thyrotoxicosis.
recommendation:
When present, skeletal muscle atrophy should be diagnosed and graded. Compensatory hypertrophy of unaffected fibers does not need to be recorded separately unless warranted by severity. Potential causes of the atrophy (e.g., primary degeneration, secondary to denervation, or spontaneously in aging animals) should be discussed in the pathology narrative. The histologic appearance of the affected myofibers, specifically regarding the presence of angulated myofibers, should be included in the narrative. When warranted by severity, additional myopathic changes, such as myofiber necrosis or degeneration, should be recorded and graded separately.references:
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Web page last updated on: March 11, 2015