Polymyositis

International Classification of Diseases for Mortality and Morbidity Statistics, 11th Revision, v2024-01

Polymyositis is an inflammatory muscle disease of unknown aetiology occurring predominantly in adults and characterised clinically by proximal muscle weakness (shoulders, arms, thighs), often with associated myalgia. Involvement of pharyngeal and oesophageal muscles may result in dysphagia and a risk of aspiration pneumonia. Myocarditis with rhythm disturbances or cardiomyopathy is a rare but serious complication. Polymyositis may be associated with other autoimmune diseases, malignancy or viral infection. Although serum muscle enzyme concentrations and electromyography are usually abnormal, definitive diagnosis requires demonstration of characteristic histological changes, including muscle necrosis, muscle fibre regeneration and diffuse infiltration by CD8+ T lymphocytes, on muscle biopsy.

sections/codes in this section (4A41.1-4A41.1)

• Juvenile polymyositis  (4A41.10)
• Paraneoplastic polymyositis  (4A41.11)
• Other specified polymyositis  (4A41.1Y)
• Polymyositis, unspecified  (4A41.1Z)

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