myopathy

Myopathy is a disease of skeletal muscle that causes weakness and reduced endurance due to primary muscle fiber dysfunction, with nerve or neuromuscular junction involvement either absent or secondary. It encompasses inherited and acquired conditions in which the muscle fibers are the main problem.

Clinical features commonly include symmetric proximal weakness, making it difficult to rise from a chair or climb stairs, and exercise intolerance. Fatigue and mild muscle atrophy may occur. Sensation and reflexes are often preserved early, helping distinguish myopathy from neuropathic disorders.

Diagnosis relies on a combination of history, examination, and targeted testing. Serum creatine kinase (CK) levels are frequently elevated. Electromyography shows a myopathic pattern with short, low-amplitude motor potentials; nerve conduction studies are typically normal. Muscle imaging (MRI or ultrasound) helps localize affected muscles. Definitive diagnosis often requires muscle biopsy and genetic testing. Biopsy findings vary by form and can include variation in fiber size, necrosis, central or rimmed vacuoles, and inflammatory infiltrates. Enzyme assays or genetic testing can identify metabolic or hereditary myopathies.

Classification includes inflammatory myopathies (polymyositis, dermatomyositis, inclusion body myositis), muscular dystrophies (Duchenne/Becker, limb-girdle dystrophies), metabolic myopathies (Pompe disease, glycogen or lipid metabolism disorders), congenital myopathies (central core disease), toxic myopathies (steroids, statins, alcohol), and endocrine myopathies (Cushing syndrome, hyperthyroidism).

Management depends on the underlying cause and aims to maintain function and quality of life. General measures include physical therapy, nutrition, and avoidance of prolonged immobilization. Specific treatments range from immunosuppressants for inflammatory forms and enzyme replacement for Pompe disease to supportive care and disease-specific therapies. Prognosis varies widely, with better outcomes in some inflammatory disorders and progressive courses in many dystrophic or metabolic forms.