Adult Dermatomyositis

Adult dermatomyositis (DM) is a systemic autoimmune condition characterised by immune-mediated inflammatory myopathy and distinctive cutaneous manifestations. It is defined by its myositis-specific antibody (MSA) profile, which determines prognosis, risk of interstitial lung disease (ILD), and crucially, the risk of underlying malignancy. DM affects adults of all ages with a peak in the 5th and 6th decades. The condition spans a clinical spectrum from classic inflammatory myopathy with skin disease to amyopathic DM, where skin disease occurs with absent or subclinical muscle inflammation.

Dermatomyositis is driven by type I interferon (IFN)-mediated innate immune activation targeting the vasculature and muscle. The pathological process in DM is distinct from other IIM subtypes, explaining its unique skin manifestations and treatment responses.

Type I Interferon Pathway

• Plasmacytoid dendritic cells produce high levels of type I IFN (IFNα/β) — the interferon signature in DM blood and tissue is the highest of all IIM subtypes
• IFN stimulates upregulation of MHC class I on muscle fibres, endothelial cells, and keratinocytes
• Drives B cell activation and autoantibody production (MSAs)
• IFN pathway is a therapeutic target — emerging JAK inhibitor evidence

Complement-Mediated Microangiopathy

• Complement membrane attack complex (MAC) deposits on endomysial capillaries — perimysial microangiopathy is the histological hallmark of DM
• Capillary loss → ischaemia → perifascicular atrophy (pathognomonic finding on muscle biopsy)
• Explains the skin and nail fold capillary changes (ragged cuticles, dilated/tortuous loops, haemorrhages)
• Explains the dermal features (V-sign, shawl sign, Gottron's papules) — cutaneous vasculopathy

MSA-Specific Pathogenic Mechanisms

Dermatomyositis presents with a characteristic combination of skin and muscle features. The skin findings are often the presenting complaint and may precede muscle involvement by months to years (amyopathic DM). Recognition of pathognomonic skin features enables early diagnosis.

Pathognomonic Skin Features

Highly Characteristic (Non-Pathognomonic) Skin Features

• V-sign — erythema over anterior neck and chest (V-neck distribution); photodistributed
• Shawl sign — erythema over posterior shoulders, upper back, and neck; photodistributed
• Mechanic's hands — hyperkeratosis, fissuring of lateral fingers and palms; typically anti-synthetase syndrome, but occurs in some DM
• Periungual changes — ragged cuticles, nailfold capillary dilatation and haemorrhages; dilated capillaries visible with ophthalmoscope at nail bed
• Holster sign — lateral thigh erythema in the holster distribution
• Scalp involvement — erythema, scaling, pruritus; may resemble psoriasis
• Skin ulceration — particularly associated with anti-MDA5; digital ulcers, periungual necrosis
• Calcinosis — rare in adult DM (more common in JDM); subcutaneous calcium deposits, painful

Muscle Features

• Symmetric proximal limb weakness — difficulty rising from low chair, climbing stairs, lifting arms above head
• Neck flexor weakness — difficulty lifting head off pillow
• Dysphagia — pharyngeal muscle involvement; aspiration risk; poor prognostic sign
• Respiratory muscle involvement — in severe disease; respiratory failure possible
• Amyopathic DM — skin features without clinical or biochemical muscle involvement for ≥6 months; CK normal; significant ILD risk still present (especially anti-MDA5)
• Hypomyopathic DM — skin features with subclinical muscle disease on MRI or biopsy only

Systemic Features by MSA Subtype

A targeted investigation strategy in DM confirms the diagnosis, identifies the MSA subtype (which determines management and screening priorities), assesses for ILD, and screens for malignancy.

• Essential
  Creatinine kinase (CK)

  Elevated in classical DM (range wide: 1–50× ULN); may be NORMAL in amyopathic DM — normal CK does NOT exclude DM.
• Essential
  MSA panel (comprehensive)

  Must include anti-MDA5, anti-TIF1γ, anti-Mi-2, anti-NXP2, anti-SAE, anti-SRP, anti-HMGCR, anti-Jo-1 and related synthetase antibodies. MSA defines DM subtype, ILD risk, and malignancy risk.
• Essential
  Myositis-associated antibodies (MAA)

  Anti-Ro52, anti-U1RNP, anti-PM-Scl — overlap syndrome markers. Anti-Ro52 co-positivity with MSA is common and worsens ILD prognosis.
• Essential
  ANA (antinuclear antibody)

  Positive in majority of DM; non-specific. Titre and pattern guide interpretation.
• Essential
  Aldolase, LDH, AST, ALT

  Muscle enzyme panel — cross-check CK; AST/ALT elevated from muscle (not liver) in DM.
• Essential
  FBC, UEC, LFTs, ESR, CRP

  Baseline; CRP may be low in DM despite active myositis. Leukocytosis suggests infection, not DM activity.
• Essential — all DM
  HRCT chest

  Screen for ILD at diagnosis. NSIP most common pattern. Anti-MDA5 → rapidly progressive ILD (OP pattern also). Baseline for monitoring.
• Essential — all adult DM
  Malignancy screening

  CT chest/abdomen/pelvis. PET-CT preferred if anti-TIF1γ or anti-NXP2 positive. Age-sex appropriate cancer screening: colonoscopy, mammography, pelvic US/CA-125 (women), PSA (men).
• Essential
  Pulmonary function tests (PFTs)

  FVC, DLCO, TLC at diagnosis. Baseline for ILD monitoring. Repeat 3–6 monthly if ILD present.
• Recommended
  MRI muscle (thigh/pelvis)

  Detects muscle oedema (active inflammation) on STIR sequences. Guides biopsy site. Useful in amyopathic DM to detect subclinical muscle disease.
• Recommended
  Skin +/- muscle biopsy

  Skin biopsy: interface dermatitis, perivascular lymphocytic infiltrate (supportive but not pathognomonic). Muscle biopsy: MAC capillary deposition, perifascicular atrophy — pathognomonic of DM. Required when diagnosis uncertain or MSA negative.
• Recommended
  Echocardiogram

  Screen for myocarditis, pericarditis, pulmonary hypertension (in ILD-associated DM).
• Recommended
  Nailfold capillaroscopy

  Dilated, tortuous capillary loops with haemorrhages — characteristic of DM and distinguishes from SLE.

Risk stratification in adult DM is guided predominantly by the MSA profile, which predicts ILD risk, malignancy risk, and likely treatment response.

Malignancy Risk Stratification

• Anti-TIF1γ positive: highest malignancy risk — adenocarcinoma (ovarian, GI, lung, breast) most common; PET-CT at diagnosis
• Anti-NXP2 positive (adults): elevated malignancy risk
• Age >60 years at DM onset: increased malignancy risk regardless of MSA
• Male sex with DM: higher malignancy risk than female DM
• Clinically amyopathic DM (CADM): same or higher malignancy risk as classical DM — do not omit screening
• Anti-Mi-2 positive: lower malignancy risk but screen is still required

ILD Severity Assessment

• HRCT pattern: OP (organising pneumonia) — usually steroid-responsive; UIP — more refractory; NSIP — intermediate; diffuse alveolar damage (DAD) — poor prognosis
• Anti-MDA5 + rapid progression on HRCT = emergency — mortality >50% without aggressive treatment
• FVC <70% predicted or DLCO <40% predicted = advanced ILD requiring immediate specialist co-management
• KL-6 serum marker (if available) — elevated in active ILD; can monitor response

Pharmacological management in adult DM is guided by MSA subtype, disease severity, and dominant clinical feature (myositis, ILD, or skin disease). High-dose corticosteroids remain the cornerstone of induction, with early addition of steroid-sparing agents.

Induction — Corticosteroids

Steroid-Sparing Immunosuppression

Anti-MDA5 DM with Rapidly Progressive ILD — Triple Therapy

Refractory Disease and Skin-Predominant DM

Directed therapy in adult DM focuses on the two major life-threatening complications: ILD and malignancy. Managing skin disease is an important quality-of-life consideration.

ILD — Directed Management

• HRCT chest at diagnosis — mandatory in all adult DM
• PFTs (FVC, DLCO) at baseline and every 3–6 months if ILD confirmed
• Pulmonology co-management for all DM-ILD — shared responsibility for monitoring and immunosuppression decisions
• Anti-MDA5 DM-ILD: triple therapy (prednisolone + tacrolimus + MMF) initiated urgently — do not delay for antibody results if clinical picture consistent
• Cyclophosphamide IV monthly × 6 for rapidly progressive ILD not responding to triple therapy
• Oxygen supplementation as required; monitor SpO2
• Pirfenidone/nintedanib — antifibrotic agents under investigation for IIM-ILD; not current standard of care
• Lung transplant referral in selected cases with end-stage ILD refractory to all immunosuppression — specialist decision

Malignancy — Directed Screening and Treatment

• CT chest/abdomen/pelvis at diagnosis — all adult DM
• PET-CT — preferred in anti-TIF1γ, anti-NXP2 positive DM or if CT inconclusive
• Gynaecological assessment: transvaginal USS + CA-125 (women) for ovarian malignancy — anti-TIF1γ association
• Colonoscopy if ≥45 years or bowel symptoms
• Mammography + PSA as age-appropriate
• Repeat annual malignancy screening for ≥3 years from DM diagnosis
• Treatment of underlying malignancy can result in DM remission — coordinate with oncology
• Paraneoplastic DM may not respond well to immunosuppression alone; treat the malignancy

Skin Disease — Management

• Strict photoprotection — SPF 50+ sunscreen daily, UV-protective clothing, hat; photodistributed skin disease is worsened by UV exposure
• Topical corticosteroids — mild potency for face (hydrocortisone 1%); moderate-high for body; limit chronic use on face
• Topical calcineurin inhibitors (tacrolimus 0.1%, pimecrolimus 1%) — steroid-sparing for facial/sensitive areas; not PBS-listed for DM
• Hydroxychloroquine 200–400 mg/day — adjunct for photosensitive skin and Gottron's papules; onset 3–6 months
• IVIG — rapid skin improvement in refractory cutaneous DM
• JAK inhibitors (baricitinib, ruxolitinib) — emerging evidence for refractory skin disease; not PBS-listed for DM
• Skin ulceration (anti-MDA5) — wound care, infection prevention; aggressive immunosuppression to treat underlying vasculopathy

Non-pharmacological care in adult DM supports muscle rehabilitation, skin protection, nutritional status, and management of immunosuppression complications.

Exercise and Rehabilitation

• Graded resistance exercise is safe and beneficial in stable DM — does not worsen inflammation
• Physiotherapy referral for all patients — graduated progressive resistance training
• During active disease: gentle range-of-motion exercises; avoid high-intensity exercise until CK stabilising
• Hydrotherapy/pool therapy — reduces joint and muscle stress; well tolerated
• Monitor CK with exercise initiation — cease if CK rising significantly
• Functional rehabilitation goals: chair rise, overhead arm use, walking distance

Skin Protection

• Daily SPF 50+ broad-spectrum sunscreen — photodistributed skin disease worsened by UV radiation
• UV-protective clothing, wide-brim hat, UV window film for cars/offices
• Avoid midday sun where possible — particularly anti-MDA5 and anti-TIF1γ patients with severe skin disease
• Moisturiser for mechanic's hands and scaling skin
• Nail care — cuticle management for periungual disease; avoid trauma to inflamed nail folds

Dysphagia — Swallowing Support

• Speech pathology referral — formal swallowing assessment for all patients with dysphagia symptoms
• Videofluoroscopic swallow study (VFSS) — assess aspiration risk and swallowing mechanics
• Modified diet textures per speech pathology recommendation
• Nasogastric or PEG feeding if severe dysphagia or aspiration pneumonia risk
• Upright positioning during and after meals

Corticosteroid Complication Prevention

• Calcium 1200 mg/day + vitamin D 1000 IU/day — all patients commencing prolonged corticosteroids
• Bisphosphonate (alendronate or risedronate) if DEXA T-score ≤−1.5 or high cumulative steroid dose anticipated
• PPI gastroprotection — all patients on NSAIDs or higher-dose corticosteroids
• Glucose monitoring — fasting BSL weekly initially; HbA1c 3-monthly on steroids
• Blood pressure monitoring
• PJP prophylaxis (co-trimoxazole 480 mg/day) — when on ≥2 immunosuppressive agents or prednisolone >20 mg/day for >1 month
• Infection surveillance — avoid live vaccines; pneumococcal and influenza vaccination recommended

Monitoring in adult DM tracks disease activity, treatment response, ILD progression, and the ongoing need for malignancy surveillance.

When to Refer

• Rheumatology: All cases — DM requires specialist management for diagnosis, MSA interpretation, ILD and malignancy coordination
• Pulmonology: All DM with ILD — co-management of ILD, PFT monitoring, respiratory support
• Oncology: Malignancy identified — particularly anti-TIF1γ/anti-NXP2 DM; treating the malignancy may resolve DM
• Speech pathology: Any dysphagia — urgent if aspiration risk
• Physiotherapy: All patients — muscle rehabilitation
• Dermatology: Severe or refractory cutaneous DM, diagnostic skin biopsy, calcinosis management
• Ophthalmology: Annual review after 5 years of hydroxychloroquine (retinopathy screening)

Several patient subgroups require modified approaches in adult DM management.

Clinically Amyopathic Dermatomyositis (CADM)

• Defined by typical DM skin features with absent muscle weakness and normal or minimally elevated CK for ≥6 months
• Previously called amyopathic DM — misleadingly implies benign course
• ILD risk is equal to or higher than classical DM — particularly anti-MDA5 CADM
• Malignancy risk is equivalent to classical DM — do not omit cancer screening
• Treatment for CADM-ILD follows the same aggressive approach as classical DM-ILD
• Muscle biopsy often shows subclinical inflammation (hypomyopathic) despite normal CK

DM with Anti-MDA5 — Rapidly Progressive ILD

• Anti-MDA5 DM is a medical emergency when ILD is rapidly progressive — can be fatal in weeks
• Early diagnosis critical: anti-MDA5 antibody should be sent urgently when CADM + ILD/dyspnoea + skin ulceration
• Triple immunosuppression: high-dose IV methylprednisolone + tacrolimus + MMF — initiate without waiting for antibody results if clinical picture consistent
• Consider tofacitinib (JAK inhibitor) — emerging evidence for anti-MDA5 rapidly progressive ILD refractory to standard therapy
• ICU liaison early — may require high-flow oxygen, non-invasive ventilation
• KL-6 and ferritin — markers of ILD activity; hyperferritinaemia in anti-MDA5 DM is a poor prognostic sign

DM in Pregnancy

• DM can flare during pregnancy; new-onset DM in pregnancy requires urgent specialist management
• Prednisolone — safe in pregnancy at lowest effective dose; use throughout gestation if needed
• Azathioprine — used when prednisolone alone insufficient; monitor foetal growth
• MMF and methotrexate — absolutely contraindicated in pregnancy; cease ≥3 months before conception
• Tacrolimus — limited safety data; use only if ILD life-threatening risk outweighs embryo risk
• IVIG — safe in pregnancy; can be used for acute flares
• Malignancy screening still required — safe imaging (USS, non-contrast MRI) preferred over CT

DM in Elderly Patients (>65 Years)

• Higher malignancy risk — particularly ovarian, GI, lung cancers; do not omit PET-CT in elderly new-onset DM
• Corticosteroid toxicity amplified — falls risk, delirium, osteoporosis, glucose dysregulation, infection
• Start prednisolone at lower dose if frail (0.5 mg/kg/day); escalate if response inadequate
• Azathioprine dose reduction may be required in renal impairment — check eGFR
• Methotrexate — avoid in eGFR <30 mL/min

Stewardship in adult DM addresses avoiding under-treatment (which risks permanent damage and death) and avoiding treatment-related harm from prolonged immunosuppression.

GP Role

• Recognise pathognomonic skin features (heliotrope rash, Gottron's papules) — enables early diagnosis
• Initial workup: CK, comprehensive MSA panel, ANA, HRCT chest, FBC, UEC, LFTs
• Urgent rheumatology referral — DM is a systemic disease requiring multidisciplinary management
• Coordinate malignancy screening — CT chest/abdomen/pelvis ± PET-CT depending on MSA
• Photoprotection education — SPF 50+ daily, UV avoidance; sun exposure worsens skin disease and may drive relapse
• Manage corticosteroid complications in primary care — glucose, BP, osteoporosis prevention
• Maintain long-term monitoring — FBC, LFTs, CK 3-monthly once stable; annual cancer screening

Long-term follow-up in adult DM focuses on disease activity monitoring, treatment optimisation, ILD surveillance, and ongoing malignancy screening.

Remission and Treatment Cessation

• Remission defined as: CK normal + no muscle weakness + no active skin disease + stable ILD (if present) for ≥6 months on stable treatment
• Treatment cessation attempted after ≥2 years of sustained remission — very slow taper
• High relapse risk — patients with anti-MDA5 DM-ILD typically require indefinite MMF/tacrolimus
• Immunosuppression cessation not appropriate if ILD present — ILD can worsen on medication withdrawal

• 01
  Lundberg IE, et al. 2017 EULAR/ACR classification criteria for adult and juvenile idiopathic inflammatory myopathies. Ann Rheum Dis. 2017;76(12):1955–1964.
• 02
  Allenbach Y, et al. New tools to assess myositis patients. Curr Opin Rheumatol. 2020;32(6):545–552.
• 03
  Rider LG, et al. Actuarial survival of adult and juvenile idiopathic inflammatory myopathies. Arthritis Care Res. 2009;61(10):1417–1427.
• 04
  Moghadam-Kia S, et al. Anti-melanoma differentiation-associated gene 5 is associated with rapidly progressive lung disease and poor survival in US patients with amyopathic and myopathic dermatomyositis. Arthritis Care Res. 2016;68(5):689–694.
• 05
  Hengstman GJ, et al. Dermatomyositis and malignancy: a report of 72 patients. Rheumatology. 2014;53(4):712–718.
• 06
  Aggarwal R, et al. Efficacy of intravenous immunoglobulin in dermatomyositis (ProDERM trial). N Engl J Med. 2022;387(16):1515–1525.
• 07
  Oddis CV, Aggarwal R. Treatment in myositis. Nat Rev Rheumatol. 2018;14(5):279–289.
• 08
  Kurasawa K, et al. Treatment of rapidly progressive interstitial lung disease with combination immunosuppressive therapy. Rheumatology. 2018;57(10):1835–1843.
• 09
  Therapeutic Guidelines. Rheumatology. Melbourne: Therapeutic Guidelines Ltd; 2024.
• 10
  Pharmaceutical Benefits Scheme (PBS). Schedule of Pharmaceutical Benefits. Canberra: Department of Health; 2025.
• 11
  Royal Australian College of General Practitioners (RACGP). Clinical guidance — dermatomyositis. Melbourne: RACGP; 2023.