Rheumatology
Dermatomyositis
피부근염
Autoimmune disease with characteristic rash and muscle weakness
- How common
- Rare (1–10 per 100,000)
- Typical age
- Bimodal: pediatric + adult
What is it?
Complement and antibodies attack muscle and skin microvasculature causing ischemic injury and characteristic rash (vasculopathy-mediated unlike PM).
Commonly affected: Skin + proximal muscles + lungs
How it develops
- Microvascular attackC5b-9 MAC attacks muscle capillaries
- Capillary dropoutCauses muscle ischemia
- Perifascicular atrophyPathognomonic perifascicular atrophy
- Skin manifestationsHeliotrope, Gottron papules, V-sign
Symptoms
- Symmetric proximal weaknessShoulder and pelvic girdle weakness
- Cancer association (25%)Lung, ovary, gastric, lymphoma
- Heliotrope rashViolaceous edematous eyelid rash
- Gottron papulesScaly papules over MCP/PIP knuckles
- Shawl/V signPhotodistributed erythema (V-neck, shoulders)
How it is examined
- Skin + strength examPathognomonic rash + proximal weakness
- Enzymes + EMG + biopsyCK ↑, myopathic EMG, perifascicular atrophy
- Cancer screeningCT (chest/abdomen/pelvis), tumor markers
Imaging
X-ray shows soft tissue calcinosis (esp. juvenile DM).
- Soft tissue calcinosis
Muscle MRI for edema, HRCT for ILD, CT for malignancy screening.
- Muscle edema
- ILD
- Soft tissue calcinosis
Non-surgical care
- High-dose corticosteroidsPrednisone 1mg/kg/day
- Combo immunosuppressantsMethotrexate, azathioprine, MMF
- IVIGEffective for both skin and muscle
- Hydroxychloroquine (skin)Helps skin manifestations
- Photoprotection/SPFRash is photosensitive
Conservative options are generally tried first. Medications listed here can have side effects — discuss them with your prescriber.
When surgery is considered
Refractory disease, associated malignancy
Procedures that may be discussed
- Rituximab
- JAK inhibitor (tofacitinib, esp. anti-MDA5)
- Cyclophosphamide (ILD)
- Treat underlying cancer
Outlook
Generally responds to therapy but malignancy/ILD worsen prognosis. 5-year survival 75–95%.