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🌱 來自: inflammatory myopathies

Definition and epidemiology of inflammatory myopathies

• All lead to skeletal muscle inflammation & weakness, variable extramuscular involvement
• Polymyositis (PM): incidence <1/million/y; onset typically 40s-50s; ♀ >♂
• Dermatomyositis (DM): similar to PM but w/ skin manifestations; incidence ~1/million/y; also occurs in childhood; malignancy a/w PM (10%) and DM (24%)
• Necrotizing autoimmune myositis (NM): usually adults; risk factors: statin exposure (⊕ anti-HMGCR; NEJM 2016;374:664), CTD, cancer, rarely viral infection; incidence unclear
• Inclusion body myositis (IBM): age >50; ♂ >♀; incidence ~5/million/y; often misdiagnosed as PM
• Ddx: drug-induced toxic myopathy (statins, cocaine, steroids, colchicine); infxn (HIV, EBV, CMV); metabolic (hypothyroid, hypo-K, hypo-Ca); neuromuscular dis. (eg, myasthenia gravis); glycogen storage disease; mitochondrial cytopathy; muscular dystrophy