Dermatomyositis (DM) is an idiopathic inflammatory myopathy characterized by pathognomonic cutaneous findings and variable muscle, lung, and systemic involvement. Cutaneous dermatomyositis (CDM) may occur with minimal or absent myositis (clinically amyopathic DM). Hallmark rashes include heliotrope erythema, Gottron papules/sign, photosensitive poikiloderma, and nailfold changes. DM is associated with myositis-specific autoantibodies (MSAs) that predict phenotypes (e.g., anti-MDA5, anti-TIF1-γ, anti-Mi-2, anti-NXP2) and guide cancer and ILD risk assessment. Management uses photoprotection, topical anti-inflammatories, systemic immunomodulators, and careful screening for interstitial lung disease (ILD) and malignancy.
Epidemiology
- Bimodal peaks: childhood (JDM) and adulthood; female predominance.
- Amyopathic/hypomyopathic DM accounts for a significant subset with prominent skin disease.
- Increased risk of ILD (notably with anti-MDA5) and malignancy (notably with anti-TIF1-γ and anti-NXP2 in adults).
Pathophysiology
- Complement-mediated microangiopathy with perivascular/perifascicular inflammation; type I interferon signature prominent.
- MSAs correlate with clinical patterns: anti-Mi-2 (classic rash, good prognosis), anti-MDA5 (ulcerative rash, rapidly progressive ILD), anti-TIF1-γ (marked photoactivity, cancer association), anti-NXP2 (calcinosis, edema).
Cutaneous Manifestations
- Heliotrope rash: violaceous periorbital discoloration and edema.
- Gottron papules: violaceous scaly papules over MCP, IP joints; Gottron sign over extensor surfaces (elbows, knees).
- Shawl/V-sign: photo-exposed poikilodermatous erythema; holster sign on lateral thighs.
- Nailfold changes: dilated capillary loops, periungual erythema, cuticular overgrowth.
- Scalp: diffuse erythema with scale, painful pruritus.
- Ulceration and palmar papules (anti-MDA5 associated); calcinosis cutis more in JDM.
Differential Diagnosis
- CLE (malar rash without Gottron lesions), psoriasis, atopic or seborrheic dermatitis, drug eruptions, photoallergy, mixed connective tissue disease, antisynthetase syndrome.
Diagnostic Workup
- Labs: CK, aldolase, LDH, AST/ALT. Enzymes may be normal in amyopathic cases.
- Autoantibodies: ANA, ENA panel; myositis-specific antibodies (Mi-2, MDA5, TIF1-γ, NXP2, SAE, Jo-1 and other antisynthetases).
- Skin or muscle biopsy: interface dermatitis with increased mucin in skin; muscle shows perifascicular atrophy and perimysial inflammation.
- Imaging: MRI of muscle for edema; HRCT and PFTs to assess ILD risk (especially with anti-MDA5, antisynthetase).
- Malignancy screening: age/sex-appropriate screening plus enhanced evaluation in high-risk serologies (e.g., CT chest/abdomen/pelvis +/- PET/CT per local protocols).
Management
- Cutaneous care
- Rigorous photoprotection (broad-spectrum SPF 50+, UV clothing), smoking cessation.
- Topicals: high-potency corticosteroids for thick plaques; calcineurin inhibitors for face; pruritus control with antipruritics.
- Antimalarials (HCQ; add quinacrine or switch to chloroquine if partial response). Note: DM often less responsive to antimalarials than CLE.
- Systemic immunomodulation
- First-line systemic: corticosteroids often used for myositis/ILD; for cutaneous-predominant DM, steroid-sparing agents:
- Methotrexate, mycophenolate mofetil, azathioprine.
- IVIG shows strong efficacy for refractory skin and muscle disease; FDA-approved for adult DM.
- Calcineurin inhibitors (tacrolimus/cyclosporine) particularly for ILD.
- Rituximab in refractory cases.
- JAK inhibitors (tofacitinib, baricitinib, upadacitinib) show promising results in anti-MDA5 and refractory cutaneous DM.
- ILD management (with pulmonary/rheumatology)
- High-risk serologies/symptoms: early HRCT and PFTs; consider combination immunosuppression (e.g., corticosteroid + calcineurin inhibitor + cyclophosphamide or mycophenolate).
- Anti-MDA5 rapidly progressive ILD: aggressive early therapy; JAK inhibitors and IVIG increasingly used.
- Malignancy surveillance
- Highest yield within first 2–3 years after onset; tailor intensity by MSA status, age, and regional cancer epidemiology.
Prognosis and Monitoring
- Cutaneous disease can be chronic and relapsing; pruritus burdensome.
- ILD and malignancy drive morbidity/mortality; early detection improves outcomes.
- Monitor labs for systemic therapy adverse effects; screen for steroid complications if used.
References (recent guidelines and key reviews)
- EULAR/ACR classification criteria and management guidance for idiopathic inflammatory myopathies, 2022–2024.
- Dermatology–rheumatology consensus on cutaneous DM evaluation and treatment, 2023–2024.
- Evidence for IVIG and JAK inhibitors in DM, 2021–2024.
- Cancer and ILD risk stratification by myositis-specific antibodies, 2022–2024.