Symptoms of adult onset Polymyositis
Characteristic clinical features of adult onset Polymyositis
• ASA syndrome and IMNM used to be included in the adult PM category but have now been separated into their own categories. Excluding these makes adult-onset PM an uncommon disease.
• Adult-onset PM has proximal muscle weakness with elevated muscle enzymes and no other cause (e.g., infection, drugs, endocrinopathy, other).
• Cardiac involvement (e.g., conduction disturbances, congestive heart failure) seen in 30%. Cannot rely on elevated CPK M/B fraction or troponin T, which are elevated in inflammatory muscle disease. Troponin I elevation is specific to cardiac involvement.
• Increased risk of associated cancer in patients aged >40 to 50 years.
• Muscle histology: endomysial more than perimysial inflammation surrounding and invading non-necrotic muscle fibers expressing major histocompatibility complex (MHC) class I antigens. Inflammatory infiltrate comprises CD8+ T cells and macrophages. Vasculature is spared.
• Good prognosis if not associated with cancer.