Synopsis
Differentiate treatable immune-mediated myopathy from inclusion-body myositis and non-inflammatory weakness, detect swallowing, respiratory, cardiac, lung and malignancy complications, and obtain tissue before prolonged immunosuppression where appropriate.
- Idiopathic inflammatory myopathies include dermatomyositis, antisynthetase-spectrum disease, immune-mediated necrotising myopathy and inclusion-body myositis; the historical label polymyositis is now used far less often after modern classification.
- Most active immune myopathies produce subacute, broadly symmetric proximal weakness affecting chair rise, stair climbing, lifting and neck flexion more than distal movement.
- Dermatomyositis clues include heliotrope eyelid change, Gottron papules over extensor joints, Gottron sign, shawl or V-neck erythema, periungual change and scalp inflammation.
Key red flags
New hypoxia, rapidly falling vital capacity, aspiration, arrhythmia, troponin elevation or severe dysphagia requires urgent multidisciplinary admission.
Investigation priorities
Quantify membrane injury and provide a treatment-response marker.
Management branches
An adult reports progressive difficulty with stairs, rising or overhead tasks.
- Measure neck, scapular, hip, knee and distal power, inspect skin and muscle bulk, and assess reflexes, sensation, bulbar function and gait.
- Review statins, steroids, alcohol, endocrine and electrolyte disease, infection, family history and exercise, obtaining CK and a targeted mimic profile.
Key medicines
PrednisoloneActive inflammatory myopathy often begins with a specialist weight-based oral regimen followed by a response- and toxicity-led taper; exact dose reflects organ threat and subtype.
MethotrexateUse a once-weekly specialist dose with folic acid and gradual titration according to the current BNF, renal function and local shared-care standard.