Dermatomyositis

Polymyositis (historically outdated), Amyopathic Dermatomyositis (when only skin affected)

Inflammatory, antibody- or T-cell-mediated autoimmune disease affecting skin and skeletal muscles, classified among idiopathic inflammatory myopathies (IIM).

Prevalence in Europe: approximately 6–7/100,000/year in adults. No specific Swiss national data available, but prevalence is comparable to Central Europe. Juvenile forms are significantly rarer (< 1/100,000). Female predominance (~2:1). Malignancy is associated in about 30% of adult cases.

According to the 2024 German Neurological Society (DGN) S2k guideline:

• Dermatomyositis (DM; includes juvenile DM)
• Anti-synthetase syndrome (ASyS)
• Overlap myositis (e.g., with SLE, Sjögren's syndrome, MCTD)
• Immune-mediated necrotizing myopathy (IMNM)
• Polymyositis (PM)
• Inclusion body myositis (IBM)

HLA associations vary by subtype. Triggers include UV exposure, infections (e.g., Coxsackie or picornaviruses), and medications (e.g., statins, antimalarials). Presence of specific myositis-specific autoantibodies (MSAs), such as anti-MDA5, is associated with a high risk of rapidly progressive interstitial lung disease (ILD). Paraneoplastic forms are frequent with anti-TIF1-γ or anti-NXP2 antibodies, particularly in patients > 50 years.

General: proximal muscle weakness, myalgia, fatigue, dysphagia (pharyngeal muscle involvement).
Cutaneous: heliotrope eyelid edema, Gottron’s papules and signs, shawl and V-signs, periungual capillary changes (telangiectasias, hyperkeratosis), poikiloderma.
Amyopathic DM (~5–20%) presents with cutaneous findings without clinically measurable muscle weakness.

Clinical evaluation including muscle strength testing and dysphagia history.
Laboratory: CK, aldolase, AST/ALT, LDH, CRP/ESR, and MSA/MAA panels.
Imaging: muscle MRI or high-resolution ultrasound to guide biopsy.
Histology: muscle and skin biopsies with immunopathological analysis.
Electromyography if clinically indicated.
Pulmonary evaluation: lung function and HRCT if ILD suspected.
Malignancy screening (especially if anti-TIF1-γ, anti-NXP2, or anti-HMGCR positive): whole-body CT or PET-CT at baseline and repeat within the first year.

Proximal limb muscles, cervical and pharyngeal muscles, shoulder girdle; skin of face, neck, décolleté, finger extensors, wrists.

Insidious onset of limb weakness over weeks to months, difficulties with lifting, combing hair, rising from seated position. Cutaneous swelling and rash with UV exposure. Constitutional symptoms and weight loss in paraneoplastic disease.

Interface dermatitis with perivascular lymphocytic infiltrates, basal cell damage, dermal mucin deposition.
Muscle biopsy: perifascicular atrophy, capillary loss, possible CD8+ infiltrates.

• Interstitial lung disease (especially with anti-MDA5)
• Myocarditis, arrhythmias
• Dysphagia with aspiration risk
• Paraneoplastic syndromes
• Calcinosis cutis (mainly juvenile DM)

5-year survival: ~95%; 10-year survival: ~84% with adequate treatment.
Poorer outcomes associated with ILD, anti-MDA5 positivity, and malignancy-associated forms.

Avoidance of UV exposure.
Routine tumor screening based on individual risk profile.
Early detection of ILD through regular imaging and lung function assessment.

1. Deutsche Gesellschaft für Neurologie. S2k-Leitlinie „Myositissyndrome“. Version 2024 (gültig bis 2027).
2. Korsten P, Feist E. Update on classification and treatment of dermatomyositis. Z Rheumatol. 2022;81:387-399.
3. Dalakas MC, Hohlfeld R. Polymyositis and dermatomyositis. Lancet. 2003;362:971-982. 
4. Dalakas MC et al. High-dose IVIG for dermatomyositis: a controlled trial. N Engl J Med. 1993;329:1993-2000. 
5. ProDERM Study Group. IVIG (Octagam®) in refractory DM: Phase III results. Presented at EULAR 2021.
6. INBUILD Trial. Nintedanib in progressive fibrosing ILD. N Engl J Med. 2019;381:1718-1727.
7. Chen Z et al. Anti-MDA5 antibody predicts rapidly progressive ILD: systematic review & meta-analysis. Arthritis Care Res. 2013;65:1316-1324. 
8. Solomon J et al. Myositis-related ILD and anti-synthetase syndrome. J Bras Pneumol. 2011;37:100-109. 
9. Wallaert B et al. Rituximab in refractory anti-synthetase syndrome. Rheumatology. 2009;48:1593-1596. 
10. Savage A et al. Paraneoplastic dermatomyositis with anti-TIF1-γ: case series and outcome data. J Skin. 2025;9:2351-2356.