⚠️ No Thai CPG identified for dermatomyositis/IIM management. This reference uses the 2022 British Society for Rheumatology (BSR) guideline (Rheumatology 2022;61:1760–68) for treatment, the 2017 EULAR/ACR classification criteria for diagnosis, and myositis-specific antibody (MSA) literature for phenotyping — international sources, explicitly flagged per your default.
Overview
Dermatomyositis (DM) is an idiopathic inflammatory myopathy (IIM) with characteristic skin findings, variable proximal muscle weakness, and a distinct capillaropathy-driven pathophysiology (complement-mediated microangiopathy, type I interferon signature) distinguishing it from polymyositis. Muscle involvement can range from severe to absent (clinically amyopathic DM, CADM).
Subtypes: classic DM, CADM (amyopathic/hypomyopathic), juvenile DM, cancer-associated DM, overlap myositis (with SSc, SLE, RA, MCTD), and anti-synthetase syndrome overlap.
Diagnosis — 2017 EULAR/ACR Classification (adult & juvenile IIM)
Weighted probability score (with/without muscle biopsy) using age at onset, muscle weakness pattern, skin findings (heliotrope rash, Gottron's papules/sign), CK/LDH/AST/ALT elevation, anti-Jo-1 positivity, dysphagia, and biopsy features. A score ≥55% probability classifies as IIM; the built-in subclassification tree then separates DM from PM/IBM/immune-mediated necrotizing myopathy based on skin involvement and biopsy findings.1
Older Bohan & Peter (1975) criteria are still widely used clinically (proximal weakness + elevated muscle enzymes + myopathic EMG + biopsy + typical rash) but lack antibody data and perform less well against modern classification.
Characteristic skin findings
- Heliotrope rash — violaceous, periorbital, often with edema
- Gottron's papules/sign — pathognomonic; over MCP/PIP/DIP joints (papules) or extensor surfaces of elbows/knees (macular sign)
- Shawl sign — erythema over posterior neck/shoulders/upper back
- V-sign — erythema over anterior neck/chest
- Mechanic's hands — hyperkeratotic, fissured skin on radial/palmar fingers — suggests antisynthetase syndrome
- Periungual/nailfold changes — capillary dilation/dropout, cuticular overgrowth
- Calcinosis cutis — more common in juvenile DM and anti-NXP2 positivity
- Cutaneous ulceration — associated with anti-MDA5
- Poikiloderma, scalp involvement (often pruritic, may mimic psoriasis/seborrheic dermatitis)
Myositis-specific antibody (MSA) phenotype map
| Antibody | Muscle disease | ILD risk | Malignancy risk | Distinctive features |
|---|---|---|---|---|
| Anti-Mi-2 | Moderate–severe, steroid-responsive | Low | Not increased | Classic cutaneous DM (Gottron, heliotrope, shawl/V-sign); good prognosis2 |
| Anti-MDA5 | Often mild/absent (CADM) | High — often rapidly progressive (RP-ILD) | Not increased | Skin ulceration, palmar papules, panniculitis, arthritis, alopecia; high short-term mortality from RP-ILD, especially East Asian cohorts3,4 |
| Anti-TIF1-γ | Variable, can be severe | Low | High (esp. age >40) | Extensive cutaneous disease, psoriasiform/hypopigmented lesions; strongest MSA malignancy association5 |
| Anti-NXP2 | Can be severe, may precede rash | Low | Increased (adult); juvenile marker | Calcinosis (esp. juvenile), dysphagia, subcutaneous edema5,6 |
| Anti-SAE | Often mild initially | Occasional | Possibly increased | Skin disease often precedes myositis; dysphagia common |
| Anti-synthetase (Jo-1, PL-7, PL-12, EJ, OJ) | Variable | High | Not increased | Antisynthetase syndrome: mechanic's hands, arthritis, fever, Raynaud's; anti-Jo-1 milder ILD than PL-7/PL-127 |
BSR guideline: routine MSA testing recommended in all IIM patients to aid diagnosis, phenotype, and prognosis (1, B, 100%). Titres should not be used to monitor disease activity.8
Initial workup
Laboratory
- CK, aldolase, AST/ALT, LDH (muscle enzyme panel — note CK may be normal in CADM or anti-MDA5 disease)
- Myositis antibody panel/immunoblot (MSA + myositis-associated antibodies)
- ANA, ESR/CRP
- Ferritin (markedly elevated in anti-MDA5 RP-ILD — tracks severity)4
Muscle assessment
- EMG — myopathic pattern with spontaneous activity (fibrillations, positive sharp waves)
- MRI (STIR/T2 fat-suppressed) — muscle edema, useful for biopsy targeting and disease activity
- Muscle biopsy — perifascicular atrophy, perivascular/perimysial inflammation, MHC-I upregulation, capillary loss (C5b-9 deposition)
Pulmonary
- PFTs with DLCO, HRCT chest — screen all adult patients for ILD, especially anti-synthetase or anti-MDA5 positive (BSR 1, B, 100%)8
Cardiac
- ECG, echocardiogram, cardiac troponin I (not troponin T — cross-reacts with regenerating skeletal muscle)8
Swallow
- Routine dysphagia screening — risk increased with anti-NXP2 and malignancy8
Malignancy screening (adult-onset DM)
All adult-onset DM patients: consider malignancy risk at diagnosis
↓
Higher-risk features
Older age at onset · male sex · dysphagia · cutaneous necrosis · rapid disease onset · resistance to immunosuppression · anti-TIF1-γ or anti-NXP2 positive · MSA-negative disease8
Older age at onset · male sex · dysphagia · cutaneous necrosis · rapid disease onset · resistance to immunosuppression · anti-TIF1-γ or anti-NXP2 positive · MSA-negative disease8
↓
CT thorax/abdomen/pelvis for at-risk patients; age/sex-appropriate cancer screening (mammography, cervical, colonoscopy, PSA per local guidance); consider tumor markers and ¹⁸F-FDG PET/CT in selected cases8
↓
Repeat surveillance typically over first 3 years post-diagnosis (highest risk window), individualized — no fixed interval established by evidence
Juvenile-onset DM is not associated with malignancy — routine cancer screening not warranted (BSR 1, B, 100%).8
Treatment (BSR 2022 guideline)
Induction — active myositis
Prednisolone 0.5–1 mg/kg/day PO (typically 40–60 mg/day); consider IV methylprednisolone if GI absorption concern (1, B, 100%)
Prednisolone 0.5–1 mg/kg/day PO (typically 40–60 mg/day); consider IV methylprednisolone if GI absorption concern (1, B, 100%)
↓
Add steroid-sparing agent early
Methotrexate, azathioprine, tacrolimus, ciclosporin, or mycophenolate mofetil (MMF) — no evidence favoring one over another as first line (2, C, 96%)
Methotrexate, azathioprine, tacrolimus, ciclosporin, or mycophenolate mofetil (MMF) — no evidence favoring one over another as first line (2, C, 96%)
↓
Taper prednisolone per clinical response, usually starting ~6 weeks after induction
↓
Adequate response
Continue steroid-sparing agent; wean steroid to lowest effective dose
Continue steroid-sparing agent; wean steroid to lowest effective dose
Refractory / severe disease
Escalate — see below
Escalate — see below
↓
Refractory myositis / severe skin / dysphagia
IVIG (1, B for severe/refractory muscle disease); Rituximab (esp. juvenile-onset, MSA-positive, lower damage burden); Cyclophosphamide (severe/refractory); Abatacept (adult refractory, 2, B)
IVIG (1, B for severe/refractory muscle disease); Rituximab (esp. juvenile-onset, MSA-positive, lower damage burden); Cyclophosphamide (severe/refractory); Abatacept (adult refractory, 2, B)
First-line prescriptions
| Agent | Adult dosing | Key notes |
|---|---|---|
| Prednisolone | 0.5–1 mg/kg/day PO (40–60 mg typical start) | Taper per response after ~6 wks; monitor bone health regardless of dose |
| Methotrexate | 15–25 mg PO/SC weekly + folic acid 5 mg (day after MTX) | Avoid/caution in ILD-predominant disease per some centers; renal dose adjustment needed |
| Azathioprine | 1–2.5 mg/kg/day PO (check TPMT/NUDT15 if available) | Alternative when MTX contraindicated or ILD present |
| Mycophenolate mofetil (Cellcept) | 1–1.5 g PO BID | Also used for ILD; teratogenic — contraception essential |
| Tacrolimus | 0.1 mg/kg/day PO divided BID, trough-guided (~5–10 ng/mL) | Preferred by some for ILD-predominant disease, esp. anti-synthetase |
| IVIG | 2 g/kg per cycle (e.g., 1 g/kg/day × 2 days or 0.4 g/kg/day × 5 days), monthly cycles | NHS England commissioning restricts to refractory/severe disease or dysphagia; ProDERM RCT supports efficacy9 |
| Rituximab (Rituxan) | 1000 mg IV × 2 doses 2 weeks apart, or 375 mg/m² weekly × 4 | Consider earlier in MSA-positive, juvenile-onset disease |
Evidence base is predominantly observational (GRADE B/C throughout) — no RCT hierarchy exists for choosing among steroid-sparing agents in adults.8
ILD management, incl. anti-MDA5 RP-ILD
Chronic IIM-ILD
Steroids ± single DMARD (azathioprine, ciclosporin, tacrolimus, MMF); escalate to rituximab or cyclophosphamide if treatment-resistant.8
Rapidly progressive ILD (anti-MDA5) — medical emergency
High clinical suspicion: anti-MDA5+, rapid dyspnea progression, fever, ↑↑ferritin, skin ulceration/palmar papules
↓
Induction: high-dose IV methylprednisolone pulse + early combination immunosuppression — ciclosporin or tacrolimus plus cyclophosphamide or rituximab, started early/concurrently rather than sequentially (2, C, 96%)8
↓
Multidisciplinary ILD-specialist respiratory input mandatory; consider triple/quadruple combination immunosuppression in East Asian cohort data given high mortality of monotherapy3,4
Ferritin and anti-MDA5 titre trends can help track treatment response, though titres are not validated for routine activity monitoring in DM broadly.4
Monitoring & associated complications
- Bone health: fragility fracture risk assessment at diagnosis and with risk-factor change, regardless of steroid dose (1, B, 100%)
- Cardiovascular: regular CV risk assessment — increased hypertension, diabetes, dyslipidemia, CAD risk
- Cardiac involvement: troponin I, ECG, echo ± cardiac MRI
- Dysphagia: routine screening; SLT/GI referral if present; consider aspiration risk
- Calcinosis: clinical exam + plain radiography, particularly anti-NXP2-positive or juvenile-onset patients
- Pregnancy: plan conception during disease remission; co-manage with maternal medicine; increased postpartum flare vigilance
- Mental health/QoL: routine screening for psychological wellbeing given impact of skin disease, pruritus, and steroid effects
References
- Lundberg IE, Tjärnlund A, Bottai M, et al. 2017 EULAR/ACR classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups. Ann Rheum Dis 2017;76:1955–64.
- Betteridge Z, McHugh N. Myositis-specific autoantibodies: an important tool to support diagnosis of myositis. J Intern Med 2016;280:8–23.
- Sato S, et al. Anti-MDA5 antibody, clinical characteristics of CADM — foundational description; reviewed in Ceribelli A et al., Clin Rheumatol and subsequent cohort studies.
- Southern China IIM cohort study on MSA-clinical phenotype associations and anti-MDA5 RP-ILD mortality, PMC12631342.
- Dermatomyositis-associated autoantibodies TIF1-γ, NXP2, MDA5 — clinical correlation review (Springer, Curr Rheumatol Rep-type chapter).
- Tansley SL, et al. Autoantibodies to a 140-kd protein (NXP2) in juvenile DM associated with calcinosis. Arthritis Rheum 2009;60:1807–14.
- Moroccan/Chinese MSA phenotype cohorts on antisynthetase syndrome features and ILD risk stratification by antibody subtype.
- Oldroyd AGS, Lilleker JB, Amin T, et al. British Society for Rheumatology guideline on management of paediatric, adolescent and adult patients with idiopathic inflammatory myopathy. Rheumatology 2022;61:1760–68.
- Aggarwal R, Charles-Schoeman C, Schessl J, et al. ProDERM study — IVIG (octagam 10%) in dermatomyositis. Medicine (Baltimore) 2021;100:e23677.
No Thai CPG located for IIM/dermatomyositis as of search date (Jul 2026); flagged per protocol. Recommend re-checking Thai Rheumatism Association resources periodically.