Dermatomyositis

ICD-11

4A41.0

Synonyms

None.

Epidemiology

Two peaks in incidence.

Definition

Rare inflammatory systemic autoimmune disease involving skin and muscle.

Aetiology & Pathogenesis

Autoimmune disease, in adults, 15% paraneoplastic (carcinomas: GI tract, lungs, breast, reproductive organs).

Signs & Symptoms

Skin: violaceous lichenoid papules on dorsal surface of the finders (Gottron's papules), similarly coloured patches over knees, elbows and malleoli (Gottron's sign), heliotrope periorbital oedema, periungual telangiectasesiae, poikiloderma, vasculitis with necrosis.
Muscles: necrosis of proximal muscle groups (hips, shoulders) with weakness and pain, dysphagia, dyspnoea; in children often calcinosis.
Systemic: acute severe form with vasculitis and visceral involvement.

Localisation

Dorsal aspects of fingers, knees, elbows, malleoli, face.

Classification

Dermatomyositis
Polymyositis (no skin involvement).
Dermatomyositis sine myositis (no muscle involvement within 2 years of rash developing).
Paraneoplastic dermatomyositis.
Juvenile dermatomyositis.
Dermatomyositis overlap syndromes, most commonly with progressive systemic sclerosis.

Laboratory & other workups

ESR rate elevated, ALT, AST, LDH and muscle enzymes, especially CPK, elevated.
ANA (40-60%), specific anti-myositis antibodies including anti-synthetase antibodies including anti-Jo-1 antibodies (may indicate a severe course with pulmonary fibrosis), ant—PL7, and others (anti-TIF1-gamma, anti-NPX2, anti-MDA-5 pulmonary interstitial disease, anti Mi-2) .
Electromyography (EMG): polyphasic potentials.
Directed muscle biopsy (when EMG abnormal).

Dermatopathology

Similar to lupus erythematosus, often non-specific. Muscle biopsy: muscle degeneration with lymphocytic infiltrates and obliterative vasculopathy.

Course

Chronic. Remission in those cases where an associated malignant tumour is successfully treated.

Complications

Respiratory failure, progressive loss of muscle function, renal impairment secondary to muscle damage, calcinosis (children), vasculitis.

Diagnosis

Clinical features (distinctive skin findings and muscle involvement), laboratory (muscle enzymes), EMG (polyphasic potentials), MRI, muscle biopsy.

Differential diagnosis

MCTD (mixed connective tissue disease = Sharp syndrome); dermatomyositis overlap with progressive systemic sclerosis and/or lupus erythematosus; trichinosis; thyrotoxic myopathy. If skin findings are not clear, wide range of myopathies.

Prevention & Therapy

Systemic corticosteroids, immunosuppression (cyclophosphamide, methotrexate, ciclosporin), high-dose intravenous immunoglobulins, bed rest, passive physiotherapy, photoprotection.

Special