Muscle disorders

Skeletal muscle is subject to a wide variety of disorders produced by toxins, genetic conditions, or autoimmune reactions. Many toxins affect the neuromuscular junction in a highly specific manner. Muscular dystrophies are genetically based and are commonly based on mutations of proteins that connect the contractile elements of the muscle fiber to the extracellular matrix. These weaken the sarcolemma and are the basis for damage to muscle fibers after ordinary contractions. Damage to weakened muscle fibers is followed by regeneration, but over time, the regenerative process becomes weakened. Other genetic conditions affect the mitochondria and often result in weakness after mild exercise. Autoimmune conditions, such as polymyositis, result in muscle fiber damage with some subsequent regeneration. Certain drugs, such as statins, can cause muscle fiber damage.