Polymyositis

Polymyositis is best understood as a clinical phenotype within the heterogeneous idiopathic inflammatory myopathy spectrum, not as a single uniform disease. Related subgroups include dermatomyositis, immune-mediated necrotizing myopathy, antisynthetase syndrome, overlap myositis, and inclusion body myositis; a patient historically labeled with polymyositis may ultimately fit one of these categories. The bedside pattern is progressive, symmetric weakness of the muscles closest to the trunk: the patient struggles to rise from a chair, climb stairs, lift the arms, or hold up the head. Muscle inflammation explains the loss of power, but the most dangerous complications may occur outside the limb muscles. Dysphagia can lead to aspiration, respiratory-muscle weakness or interstitial lung disease can impair ventilation, and cardiac involvement can produce arrhythmia or ventricular dysfunction. A high creatine kinase supports muscle injury but does not establish the diagnosis or measure the whole disease burden. Assessment must connect the weakness pattern with objective strength testing, swallowing and respiratory findings, laboratory studies, imaging, and—when needed—biopsy or specialist evaluation.