Dermatomyositis

Related Subjects: |Relapsing Polychondritis |Reactive Arthritis |Raynaud's Phenomenon |Polymyositis |Dermatomyositis |Polyarteritis nodosa |Osteoporosis |Rheumatoid Arthritis |Systemic Sclerosis (Scleroderma) |Rheumatology Autoantibodies |Overlap Syndrome |Inclusion Body Myositis |Inflammatory Myopathies |Psoriatic Arthritis |Adult Onset Still's Disease |Alkaptonuria |Behcet's Syndrome

🌸 Dermatomyositis is a multi-organ idiopathic inflammatory disorder characterized by proximal skeletal muscle weakness, muscle inflammation, and distinct skin manifestations.
👉 In summary: Myositis + Rash ± Cancer.

🧬 About

• Idiopathic inflammatory myositis with an associated vasculopathy.
• ≈ 10% association with malignancy (lung, breast, ovary, gut most common).
• Malignancies usually occur within the first 5 years of symptom onset.

🌺 Unlike polymyositis, dermatomyositis has classic skin findings: heliotrope rash (purple eyelids) + Gottron’s papules (scaly plaques on knuckles). ⚠️ Always think of an underlying cancer.

📊 Epidemiology

• Commoner in females (peak 40–50 years).
• Strongly associated with anti-Jo-1 antibodies (especially with lung disease).

🎗️ Associated Malignancies

• Nasopharyngeal carcinoma (esp. in Asian populations).
• Ovarian & breast cancer.
• Gastric, colon, lung cancer.
• Melanoma, non-Hodgkin lymphoma (NHL).

🩺 Clinical Features

• 💪 Symmetrical proximal muscle weakness – difficulty climbing stairs, rising from chair, or lifting arms.
• 🩸 Muscles tender/swollen; systemic features: arthralgia, weight loss.
• 🌸 Skin signs:
  • Heliotrope rash (eyelids + periorbital oedema).
  • Gottron’s papules (knuckles, elbows, knees).
  • Shawl sign (photosensitive rash over shoulders/back).
  • “Mechanic’s hands” (cracked rough fingertips).
  • Nailfold telangiectasia.
• Respiratory: may cause interstitial lung disease & respiratory muscle weakness.

🔬 Investigations

• Bloods: ↑ CK (up to 50×), LDH, AST/ALT. FBC: ± anaemia. ESR variable.
• Muscle biopsy: chronic inflammatory infiltrates + fibre necrosis.
• Skin biopsy: interface dermatitis & perivascular inflammation.
• MRI: detects inflamed muscles.
• EMG: fibrillations, low-amplitude polyphasic potentials.
• Autoantibodies:
  • ANA: positive in 80%.
  • Anti-Jo-1: linked to myositis + ILD + mechanic’s hands + Raynaud’s.
  • Anti-SRP: severe disease, poor prognosis.
• 🔎 Always perform screening for occult malignancy (CT chest/abdomen/pelvis ± pelvic ultrasound in women).

💊 Management

• 🤝 Multidisciplinary care (rheumatology, neurology, oncology).
• 📉 Steroids: Prednisolone 0.5–1 mg/kg tapered. CK falls early, strength lags.
• 🛡️ Immunosuppressants: Methotrexate, azathioprine, mycophenolate for resistant cases.
• 💉 Severe disease: IV methylprednisolone ± IVIG or biologics (rituximab).
• 🌞 Sun protection for skin disease.

📚 References

• Dermatomyositis – BMJ Best Practice

Cases — Dermatomyositis

• Case 1 — Classic skin + muscle features 💪👩‍🦰: A 42-year-old woman presents with progressive proximal muscle weakness (difficulty climbing stairs, lifting arms) and a violaceous rash on the eyelids (heliotrope rash). Exam: Gottron’s papules over MCP joints. CK markedly elevated. Diagnosis: dermatomyositis. Managed with corticosteroids and physiotherapy.
• Case 2 — Malignancy-associated 🎗️: A 61-year-old man reports weight loss, dysphagia, and proximal weakness. Exam: shawl sign (photosensitive rash across shoulders/back). Investigations show raised CK and positive anti-TIF1-γ antibody. CT chest/abdomen/pelvis: underlying bronchogenic carcinoma. Diagnosis: paraneoplastic dermatomyositis. Managed with immunosuppression and treatment of malignancy.
• Case 3 — Interstitial lung disease 🫁: A 35-year-old woman with known dermatomyositis develops exertional breathlessness and dry cough. HRCT chest: interstitial lung disease. Serology: anti-Jo-1 (anti-synthetase antibody) positive. Diagnosis: anti-synthetase syndrome with dermatomyositis. Managed with steroids, azathioprine, and pulmonary follow-up.

Teaching Point 🩺: Dermatomyositis is an idiopathic inflammatory myopathy with characteristic cutaneous signs (heliotrope rash, Gottron’s papules) and proximal muscle weakness. Always screen for associated malignancy and monitor for lung involvement.