Myopathies
Muscle disease (myopathy) can be acquired or hereditary. Symptoms include skeletal muscle weakness, atrophy, muscle cramps or myalgias, and impaired function of respiratory, pharyngeal, facial, or ocular muscles. Clinicians must identify treatable myopathies and initiate therapy before permanent weakness occurs. For patients with untreatable disorders, proper supportive care, rehabilitation, genetic counseling, and psychological support are critical. This chapter covers common myopathies, including muscular dystrophies; malignant hyperthermia; metabolic myopathies; mitochondrial myopathies and encephalopathies; ion channelopathies, periodic paralyses, and nondystrophic myotonias; and drug-induced myopathies. Clinical presentation, diagnosis, pathogenesis, and therapy are emphasized. Tables describe genetic classification of the limb-girdle and distal muscular dystrophies; proteins involved in myofibrillar myopathy; other distal myopathies; and antirheumatic, antiinflammatory, and immunosuppressive drug-induced myopathy. Figures show the sarcolemmal membrane and enzymatic proteins associated with muscular dystrophies, sarcomeric and nuclear proteins associated with muscular dystrophies, and major metabolic pathways used by muscle. This chapter contains 3 highly rendered figures, 4 tables, 107 references, and 5 MCQs.