Polymyositis / Dermatomyositis

Immune-mediated myopathies include dermatomyositis, polymyositis, overlap myositis, necrotising autoimmune myopathy (NAM) and inclusion body myositis (IBM), managed per the British Society for Rheumatology’s dedicated 2022 myositis guideline (registry: bsr-myositis-2022; verified 2026-07-23 — cited by name only, full guideline text not independently fetched).

Classifying immune-mediated myopathies

• Dermatomyositis — adult (with or without malignancy) or juvenile
• Polymyositis
• Overlap myositis — myositis associated with another connective tissue disorder (SLE, mixed connective tissue disease, Sjögren, RA); or antisynthetase syndrome (fever, arthralgia, Raynaud phenomenon, interstitial lung disease, mechanic’s hands — associated with anti-tRNA synthetase antibodies, especially anti-Jo-1)
• Necrotising autoimmune myopathy (NAM) — HMGCR-positive (statin- associated or statin-naive) or SRP-positive; associated with malignancy, connective tissue disease, or viral infection (HIV, hepatitis C)
• Inclusion body myositis (IBM)
• Rarer causes — eosinophilic myositis/myofasciitis, infection-related myositis, granulomatous myositis (including sarcoid-associated)

Clinical features

• Muscle weakness: difficulty raising arms above the shoulders, climbing steps, or rising from sitting; can progress to wheelchair use/bedbound status from pelvic/shoulder girdle weakness. Severe neck flexor involvement can cause inability to lift the head from a pillow. Pharyngeal/upper oesophageal involvement can impair swallowing and cause aspiration risk. Hands, feet and face are spared except in IBM.
• Polyarthralgia or polyarthritis
• Visceral involvement (less common than in other rheumatic disease): interstitial lung disease; cardiac conduction disturbance and ventricular dysfunction; GI involvement (more common in children, via vasculitis — abdominal pain, haematemesis, melaena, ischaemic bowel perforation)
• Skin changes — see dermatomyositis below

Diagnosis

• CK/LDH/AST/ALT elevated
• Electromyography
• MRI — identifies oedema in affected muscle and can help target biopsy
• Muscle biopsy — confirms the diagnosis

Management

Specialist referral — lifelong treatment and monitoring required.

• Exercise under neurophysiotherapy guidance
• First-line: high-dose prednisolone (e.g. 75mg) + a steroid-sparing agent (azathioprine, methotrexate, mycophenolate)
• Severe disease: IV methylprednisolone, IVIg

Dermatomyositis

Muscle inflammation (myositis) with a characteristic cutaneous eruption, which usually precedes muscle weakness onset. Main cutaneous signs:

• Periorbital reddish-purple erythema (heliotrope rash)
• Flat-topped papules over the dorsal interphalangeal joints (Gottron papules)
• Erythema over the dorsal knuckles (Gottron sign)
• Photodistributed erythema/oedema on the sun-exposed neck and shoulders (shawl sign)
• Characteristic nailfold changes and ragged cuticles

Heliotrope eyelids:

Gottron papules:

Nail folds in dermatomyositis:

Sun-exposed sites:

Dermatomyositis management

• Co-managed by dermatology and rheumatology.
• Topical corticosteroids and hydroxychloroquine are first-line; methotrexate and azathioprine for resistant cases.
• Sun exposure exacerbates disease — stress broad-spectrum sun protection.
• Associated with malignancy in ~25% of adults — consider paraneoplastic dermatomyositis, especially in older patients.
• Dermatomyositis in children is not associated with neoplasia — investigations to exclude occult malignancy are not necessary.