Synopsis
Recognise inflammatory myopathy from objective weakness, characteristic skin and organ features, exclude common mimics and inclusion-body myositis, investigate dysphagia, lung and malignancy risk, and restore function with prompt steroid-sparing treatment.
- Suspect inflammatory myopathy with subacute symmetrical proximal weakness affecting stairs, rising, lifting and hair care; distinguish inability from pain, fatigue and breathlessness.
- Dermatomyositis signs include heliotrope oedema, Gottron papules or sign, shawl or V-sign erythema, periungual capillary change, scalp inflammation and mechanic hands.
- True polymyositis is a diagnosis of exclusion; reconsider inclusion-body myositis, immune-mediated necrotising myopathy, antisynthetase disease, drug, endocrine and inherited causes before applying it.
- Check CK, aldolase, AST, ALT and LDH, but normal CK does not exclude dermatomyositis, clinically amyopathic disease or dangerous ILD.
- Use myositis-specific antibodies for phenotype and risk, not as stand-alone diagnoses; MDA5 raises rapidly progressive ILD concern and TIF1-gamma increases malignancy vigilance.
- MRI identifies oedema and a suitable biopsy site; EMG supports a myopathic process and excludes mimics; muscle or skin biopsy remains important when phenotype and serology do not secure diagnosis.
- Screen swallowing and respiratory strength at baseline and whenever voice, cough, aspiration, orthopnoea or morning headache appears; do not wait for profound limb weakness.
- Start glucocorticoid promptly for active muscle disease and add a steroid-sparing agent early; combine treatment with physiotherapist-led progressive exercise rather than prolonged rest.
- Treat IVIG as an important option for severe dysphagia, refractory muscle or skin disease and selected pregnancy situations; use specialist weight-based dosing and thrombosis or renal safeguards.
- Complete routine national cancer screening and add risk-stratified investigation near disease onset based on age, symptoms, examination, antibody phenotype and shared decision-making.
Key red flags
Choking, wet voice, nasal regurgitation, recurrent pneumonia or inability to handle secretions requires urgent speech-and-language and respiratory assessment.
Weak cough, orthopnoea, morning headache, declining FVC or hypercapnia suggests respiratory muscle failure and may need non-invasive or invasive support.
Rapid hypoxia with ground-glass or organising change may represent myositis-associated ILD, infection, aspiration, haemorrhage or oedema.
Chest pain, palpitations, syncope, troponin rise or conduction change requires urgent myocarditis and arrhythmia assessment.
New dermatomyositis, weight loss, lymphadenopathy, dysphagia or treatment-refractory disease requires age-, sex- and phenotype-informed malignancy evaluation.
Wet voice, coughing with meals, nasal regurgitation, weight loss and recurrent chest infection indicates dysphagia and aspiration risk.
Orthopnoea, weak cough, reduced chest expansion, low supine FVC or hypercapnia can progress to ventilatory failure.
Investigation priorities
Quantify muscle injury, detect rhabdomyolysis complications and create a response baseline.
Management branches
Subacute proximal weakness, dermatomyositis rash or unexplained CK elevation raises inflammatory-myopathy suspicion.
- Measure functional and manual strength, skin, joints, sensation, reflexes, swallowing, cough and respiratory symptoms and review statin, steroid, endocrine and family history.
- Obtain enzymes, renal and urine, thyroid, inflammatory and phenotype-directed myositis antibodies, then MRI and EMG to select further testing.
- Obtain muscle or skin biopsy when the diagnosis, subtype or mimic remains uncertain, without delaying organ-saving treatment in a severe classic presentation.