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 an idiopathic inflammatory myopathy with characteristic cutaneous features and variable skeletal muscle involvement. Typical features include symmetrical proximal muscle weakness, a heliotrope rash (violaceous periorbital rash), and Gottron’s papules/sign over the MCP/PIP joints and extensor surfaces. ⚠️ In adult-onset disease, always think about associated malignancy, especially in higher-risk phenotypes.

🧬 About

• Immune-mediated inflammatory myopathy with prominent microangiopathy / vasculopathy, skin disease, and possible systemic involvement.
• May affect muscle, skin, lungs, swallowing, and occasionally the heart.
• Adult-onset dermatomyositis has a recognised association with occult malignancy; risk is highest around the time of disease onset.

📊 Epidemiology

• Rare condition; more common in women.
• Occurs in both children and adults.
• Adult-onset disease carries malignancy risk; juvenile dermatomyositis is not routinely associated with cancer.

🎗️ Malignancy Association

• Think particularly about malignancy in adult-onset disease, especially if there is older age at onset, male sex, dysphagia, cutaneous necrosis/ulceration, rapid onset, poor response to immunosuppression, or anti-TIF1-γ / anti-NXP2 positivity.
• Common associated cancers include lung, ovarian, breast, colorectal/gastrointestinal, and lymphoma.
• Nasopharyngeal carcinoma is particularly relevant in some East and South-East Asian populations.
• Continue routine age- and sex-appropriate national cancer screening as well as targeted assessment where indicated.

🩺 Clinical Features

• 💪 Symmetrical proximal muscle weakness – difficulty climbing stairs, rising from a chair, washing hair, or lifting arms overhead.
• 🌸 Skin signs:
  • Heliotrope rash with periorbital oedema.
  • Gottron’s papules/sign over knuckles, elbows, or knees.
  • Shawl sign / V-sign – photosensitive erythema over shoulders, upper chest, or back.
  • Mechanic’s hands – hyperkeratotic, cracked fingertips (especially with antisynthetase overlap).
  • Nailfold telangiectasia.
  • Scalp erythema/pruritus may occur.
• 🫁 Lung involvement: interstitial lung disease, especially in antisynthetase or anti-MDA5 phenotypes.
• 🍽️ Dysphagia may occur and is clinically important because of weight loss and aspiration risk.
• ❤️ Occasionally associated with cardiac involvement.
• ⚖️ Constitutional features may include fatigue, weight loss, arthralgia, and reduced exercise tolerance.

🔬 Investigations

• Bloods: CK may be raised (but can be normal, especially in some phenotypes); also check AST/ALT, LDH, CRP/ESR, FBC, U&Es, LFTs, bone profile.
• Autoantibodies: request a myositis-specific / myositis-associated antibody panel.
  • Anti-TIF1-γ, anti-NXP2 → malignancy risk markers in adult-onset disease.
  • Anti-MDA5 → risk of rapidly progressive ILD.
  • Anti-Mi-2 → classic cutaneous dermatomyositis phenotype.
  • Anti-Jo-1 and other antisynthetase antibodies → antisynthetase syndrome / ILD / mechanic’s hands / Raynaud’s.
• MRI muscle: useful to identify inflamed muscle and guide biopsy.
• EMG: supports a myopathic process but is not diagnostic on its own.
• Muscle biopsy: classically shows perifascicular atrophy with perivascular/perimysial inflammation.
• Skin biopsy: may support the diagnosis where rash is prominent.
• Screen for ILD in higher-risk patients with chest imaging, pulmonary function tests (including gas transfer), and HRCT where indicated.
• Assess swallowing if dysphagia is suspected.
• Consider cardiac screening with ECG, echocardiography, and troponin I if clinically indicated.
• Malignancy screen: tailored to risk profile; in higher-risk adult patients consider CT thorax/abdomen/pelvis and further targeted tests as indicated.

💊 Management

• 🤝 Specialist MDT care – usually rheumatology ± neurology, dermatology, respiratory, SALT, physiotherapy, and oncology where needed.
• 📉 Glucocorticoids are usually first-line induction therapy.
• 🛡️ Add a steroid-sparing immunosuppressant early in many patients (for example methotrexate, azathioprine, mycophenolate, tacrolimus/ciclosporin depending on phenotype and organ involvement).
• 💉 Refractory / severe disease: consider IV methylprednisolone, IVIG, rituximab, or cyclophosphamide in specialist care.
• 🌞 Sun protection is important for cutaneous disease.
• 🏃 Exercise / rehabilitation with specialist physiotherapy or OT should be part of routine care.
• 🦴 Assess bone protection if prolonged steroids are used.
• 🍽️ Actively manage dysphagia, aspiration risk, nutrition, and respiratory complications.

🧾 Comparison of Inflammatory Myopathies

Teaching point 🩺: In adult-onset dermatomyositis, think in three parallel directions: muscle disease, skin disease, and systemic associations (especially malignancy, ILD, and dysphagia). Anti-Jo-1 is more suggestive of an antisynthetase phenotype than “classic dermatomyositis”, while anti-TIF1-γ and anti-NXP2 are more helpful when thinking about cancer risk.

*Pure polymyositis is now considered much less common than older textbooks suggested, and modern practice often reclassifies patients into other inflammatory myopathy subtypes.