Juvenile Dermatomyositis

Juvenile dermatomyositis (JDM) is the most common idiopathic inflammatory myopathy of childhood, characterised by immune-mediated proximal muscle weakness and pathognomonic skin features. Unlike adult dermatomyositis, JDM is typically not associated with underlying malignancy. It is a vasculopathic condition driven by type I interferon-mediated complement deposition in small vessels of muscle and skin. JDM predominantly affects children between the ages of 5 and 10 years, with a female predominance. Early recognition and treatment are essential to prevent long-term complications, particularly calcinosis and joint contractures.

JDM is driven by type I interferon (IFN)-mediated autoimmune vasculopathy. Complement activation on endomysial capillaries leads to vessel damage, ischaemia, and the characteristic perifascicular atrophy seen on muscle biopsy. The interferon signature in JDM is distinct from adult DM and has been used as a biomarker of disease activity.

Key Pathogenic Mechanisms

• Type I IFN pathway activation — plasmacytoid dendritic cell-derived IFN drives MHC class I upregulation on muscle and keratinocytes
• Complement membrane attack complex (MAC) deposition on endomysial capillaries — vessel loss → perifascicular ischaemia
• B cell-driven autoantibody production — MSAs correlate with clinical subtype
• Vasculopathy is more prominent in JDM than adult DM — explains calcinosis and lipodystrophy

MSA-Defined Subtypes in JDM

JDM presents with a combination of skin and muscle features. The onset may be subacute over weeks to months. Skin findings often precede muscle weakness. Recognition of pathognomonic features is key to early diagnosis.

Pathognomonic Skin Features

Characteristic (Non-Pathognomonic) Skin Features

• V-sign — erythema over anterior neck and upper chest; photodistributed
• Shawl sign — erythema over posterior shoulders, upper back, and neck
• Periungual changes — ragged cuticles, dilated nailfold capillaries (visible with ophthalmoscope); capillary abnormalities are a key disease activity marker
• Facial erythema — malar rash may occur; does not spare nasolabial folds (unlike SLE)
• Skin ulceration — associated with anti-MDA5 and severe vasculopathy; periungual necrosis; digital ulcers
• Calcinosis cutis — subcutaneous calcium deposits; particularly associated with anti-NXP2; can be extremely painful and disabling; associated with treatment delay
• Lipodystrophy — partial loss of subcutaneous fat; associated with anti-TIF1γ; can affect insulin resistance

Muscle Features

• Symmetric proximal limb weakness — difficulty climbing stairs, rising from floor, lifting overhead, combing hair
• Gower's sign positive — child uses hands to push up from floor to stand; a specific test for proximal lower limb weakness
• Neck flexor weakness — head lag when sitting up; inability to lift head off pillow
• Dysphonia and dysphagia — pharyngeal/palatal muscle involvement; aspiration risk
• Respiratory muscle weakness — rare but life-threatening; requires urgent assessment
• Muscle pain (myalgia) — common but not universal; muscle tenderness on palpation
• Functional impairment — inability to walk, dress, or perform school activities

Systemic Features

• Constitutional symptoms — fever, fatigue, weight loss, irritability; common at onset
• Arthritis — large and small joint arthritis; may precede myositis; occurs in ~50%
• Gastrointestinal vasculopathy — abdominal pain, melaena, haematemesis; rare but life-threatening in severe JDM
• Cardiac involvement — myocarditis, arrhythmias; rare; echocardiogram at baseline
• ILD — less common than adult DM but important in anti-MDA5 JDM
• Macrophage activation syndrome (MAS) — rare but severe complication; haemophagocytosis; presents with fever, cytopaenias, hyperferritinaemia, hepatosplenomegaly

Investigations in JDM confirm the diagnosis, assess severity, identify the MSA subtype, and screen for complications. Unlike adult DM, malignancy screening is NOT routinely required.

• Essential
  Creatinine kinase (CK)

  Elevated in majority of JDM but may be normal in amyopathic presentations. Normal CK does NOT exclude JDM. Can be used to monitor treatment response.
• Essential
  MSA panel

  Anti-TIF1γ, anti-NXP2, anti-MDA5, anti-Mi-2, anti-SRP, anti-HMGCR, anti-Jo-1. MSA guides prognosis, risk of calcinosis, and ILD risk.
• Essential
  Myositis-associated antibodies (MAA)

  Anti-Ro52, anti-U1RNP — overlap syndrome markers.
• Essential
  ANA

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

  Muscle enzyme panel; AST/ALT elevated from muscle not liver.
• Essential
  FBC, UEC, LFTs, ESR, CRP

  Baseline; ferritin for MAS screen. CRP may be low despite active disease.
• Essential
  Ferritin

  Elevated in MAS; also elevated in active JDM. Serial monitoring.
• Essential — all JDM
  HRCT chest

  Screen for ILD. Anti-MDA5 JDM particularly. Baseline for monitoring.
• Essential
  Pulmonary function tests

  Baseline FVC, DLCO. Repeat if ILD or respiratory symptoms.
• Recommended
  MRI muscle (thigh/pelvis)

  Gold standard for detecting active myositis — STIR sequence shows muscle oedema. Guides biopsy site. Useful to quantify extent of muscle involvement.
• Recommended
  Nailfold capillaroscopy

  Dilated, tortuous capillary loops with haemorrhages — characteristic; important disease activity marker; loss of capillary density = poor prognosis.
• Recommended
  Muscle biopsy (with MRI guidance)

  Perifascicular atrophy + MAC deposits on capillaries — pathognomonic. Required when diagnosis uncertain or MSA negative.
• Recommended
  Echocardiogram

  Screen for myocarditis, pericardial effusion, pulmonary hypertension.
• Recommended
  Bone density (DXA)

  Baseline bone density — at risk of osteoporosis with prolonged corticosteroids and restricted mobility.

Risk stratification in JDM is guided by clinical features, MSA profile, degree of functional impairment, and presence of complications.

Disease Activity Assessment Tools

• Childhood Myositis Assessment Scale (CMAS) — validated functional measure for JDM; 0–52 score; assesses 14 functional tasks (leg raise, sitting up, etc.); standard outcome tool in JDM clinical care
• Manual Muscle Testing 8 (MMT8) — 8 muscle group strength score (0–80); used alongside CMAS
• Physician Global Assessment (PhGA) — physician global assessment of disease activity (0–10 VAS)
• Nailfold capillaroscopy — Nailfold capillaroscopy score correlates with disease activity
• CK and aldolase — guide treatment response but do not always correlate with functional activity
• MRI STIR — muscle oedema on MRI correlates with active myositis; can be used to monitor response to treatment

Pharmacological management in JDM requires aggressive early treatment to prevent long-term complications, particularly calcinosis. Treatment should be initiated promptly after diagnosis — delayed treatment is the primary risk factor for calcinosis development.

First-Line — Corticosteroids

First-Line Steroid-Sparing — Methotrexate

Second-Line / Refractory JDM

Refractory/Calcinosis-Specific Agents

• Rituximab — B cell depletion for refractory JDM; strong evidence in juvenile IIM; anti-CD20; specialist-only
• Abatacept (CTLA4-Ig) — T cell costimulation blockade; emerging evidence in JDM; specialist-only
• Anti-TNF (infliximab, adalimumab) — evidence emerging for calcinosis treatment; may reduce calcinosis progression
• Diltiazem — limited evidence for calcinosis; may slow progression in some patients; generally second-line
• Bisphosphonates (pamidronate) — used for painful calcinosis; may help reduce deposits
• JAK inhibitors (baricitinib, ruxolitinib) — emerging for refractory skin disease and ILD; not PBS-listed for JDM

Directed therapy in JDM targets the major complications: calcinosis prevention, ILD management, dysphagia, and skin disease.

Calcinosis — Prevention and Management

• Calcinosis prevention — the most effective strategy is early, aggressive treatment of active JDM; treatment delay is the single greatest risk factor
• Anti-NXP2 MSA carries the highest calcinosis risk — monitor closely from diagnosis
• Calcinosis assessment: plain radiographs (calcium deposits visible); ultrasound; MRI for deep deposits; correlate with disease activity
• Established calcinosis treatment: anti-TNF agents (infliximab, adalimumab) — some evidence for regression; bisphosphonates (pamidronate) — may stabilise; diltiazem — limited evidence
• Surgical excision — for focal, superficial calcinosis causing skin breakdown, infection, or nerve compression; excision only once inflammation controlled
• Wound care — calcinosis deposits that extrude through skin require meticulous wound care and infection prevention

ILD — Management in JDM

• HRCT chest at diagnosis — all JDM; less common than adult DM but important in anti-MDA5 JDM
• Anti-MDA5 JDM-ILD — treat with prednisolone + cyclosporin or MMF; tacrolimus if severe
• PFTs baseline and 3–6 monthly if ILD confirmed
• Pulmonology co-management for all JDM-ILD

Dysphagia Management

• Speech pathology referral for all patients with dysphagia
• Video fluoroscopic swallow study (VFSS) to assess aspiration risk
• Modified diet textures and positioning
• Nasogastric feeding if severe dysphagia or aspiration risk
• IVIG and intensified immunosuppression for pharyngeal muscle weakness

Skin Disease Management

• Strict photoprotection — SPF 50+ sunscreen daily, UV-protective clothing; photodistributed skin disease is worsened by UV exposure
• Topical corticosteroids — mild potency for face; moderate-high for body; limit chronic facial use
• Hydroxychloroquine — adjunct for photosensitive skin and Gottron's papules
• Sun avoidance education — particularly important in children who spend time outdoors
• IVIG — effective for refractory cutaneous JDM

Non-pharmacological care in JDM addresses muscle rehabilitation, prevention of contractures, skin protection, school participation, and psychosocial support.

Exercise and Physiotherapy

• Physiotherapy referral for all JDM patients — graduated exercise program essential to prevent contractures
• During active disease: gentle passive range-of-motion exercises; avoid high-intensity exercise
• As disease activity reduces: progressive resistance training; hydrotherapy/pool therapy well tolerated
• Contracture prevention — regular stretching program, splinting for hip flexor, Achilles tendon, wrist contractures if developing
• Occupational therapy — assess school and home functioning; adaptive equipment for daily activities
• Monitor for Achilles tendon contracture (common in JDM) — physiotherapy intervention critical

School and Psychosocial Support

• School re-engagement planning — involve school in management; fatigue management; physical education modification
• Psychological support — chronic illness, altered appearance (calcinosis, lipodystrophy), and treatment side effects (weight gain, cushingoid features) impact self-esteem
• Peer support and disease education — normalise JDM experience; connect with Arthritis Australia or JDM peer groups
• Adolescent transition planning — transition to adult rheumatology from approximately 17–18 years

Corticosteroid Complication Management

• Growth monitoring — plot height and weight at every visit; prolonged corticosteroids suppress growth velocity
• Calcium 500–1000 mg/day + vitamin D 400–1000 IU/day — all children on corticosteroids
• DXA bone density at baseline and annually; bisphosphonate if significant Z-score decline
• Ophthalmology review — posterior subcapsular cataract with prolonged steroid use; annual review
• Blood pressure monitoring at every visit
• Fasting glucose — hyperglycaemia with high-dose corticosteroids
• Live vaccines contraindicated during active immunosuppression — document vaccination status before starting treatment

Monitoring in JDM tracks disease activity, treatment response, and complications of both the disease and its treatment.

When to Refer

• Paediatric Rheumatology: All cases — JDM requires specialist management from diagnosis. Do not delay referral while investigating.
• Paediatric Pulmonology: All JDM with ILD or respiratory symptoms
• Physiotherapy: All patients — muscle rehabilitation and contracture prevention
• Occupational Therapy: Functional assessment and adaptive strategies for school and home
• Speech Pathology: Any dysphagia
• Dermatology: Severe or refractory skin disease, calcinosis management, skin biopsy
• Psychology: Psychosocial impact, body image concerns, school re-engagement
• Ophthalmology: Annual review on hydroxychloroquine; steroid-induced cataract monitoring

Several subgroups of JDM patients require modified approaches.

Severe JDM with GI Vasculopathy

• GI vasculopathy in JDM is life-threatening — abdominal pain, haematemesis, perforation, intestinal ischaemia
• Urgent hospital admission; nil by mouth; IV methylprednisolone pulse; IV ciclosporin or cyclophosphamide
• Surgical consult if signs of perforation or peritonitis
• This is a paediatric rheumatology emergency — ICU involvement may be required

Macrophage Activation Syndrome (MAS)

• Rare but life-threatening complication — haemophagocytosis triggered by active JDM or infection
• Features: persisting fever; cytopenia (falling WBC, Hb, platelets); hyperferritinaemia (>500 μg/L, often >10,000); hepatosplenomegaly; coagulopathy; elevated LDH
• Distinguish from active JDM flare — MAS has falling cell counts, very high ferritin, coagulopathy
• Treatment: high-dose IV methylprednisolone; ciclosporin; anakinra (IL-1 inhibitor) for refractory cases; IVIG
• Bone marrow biopsy — haemophagocytosis confirms diagnosis

Adolescents with JDM

• Disease may persist into adulthood — requires adult rheumatology transition at approximately 17–18 years
• Teratogenicity counselling for MTX and MMF — essential for adolescent females of childbearing age
• Mental health assessment — body image, depression, social isolation are common
• Compliance with medication and monitoring can be challenging — motivational approaches and empowerment

Amyopathic JDM

• Typical JDM skin disease with absent clinical or biochemical myositis for ≥6 months
• ILD risk remains significant — particularly anti-MDA5 amyopathic JDM
• Do not undertreat — skin disease and ILD require active management
• Nailfold capillaroscopy and MRI muscle can detect subclinical vasculopathy and muscle disease

Stewardship in JDM focuses on preventing treatment-related harm while ensuring sufficient early immunosuppression to prevent calcinosis and long-term disability.

GP Role

• Recognise pathognomonic features (heliotrope rash, Gottron’s papules, proximal weakness in a child) — enables early diagnosis
• Urgent paediatric rheumatology referral — do not delay for muscle biopsy; referral based on clinical suspicion
• Initial bloods: CK, comprehensive MSA panel, ANA, FBC, UEC, LFTs, aldolase, ferritin
• HRCT chest if any respiratory symptoms
• Coordinate photoprotection education and skin care
• Long-term monitoring of immunosuppression complications in primary care — growth, BP, glucose, ophthalmology
• Ensure vaccination history is up-to-date before starting treatment; live vaccines contraindicated on immunosuppression

Long-term follow-up in JDM is essential — JDM has a monocyclic, polycyclic, or chronic continuous disease course. Many children require treatment for years.

Remission and Treatment Cessation

• Remission: CK normal + CMAS ≥48/52 + no active skin disease + normal nailfold capillaroscopy for ≥6 months on stable treatment
• Attempt treatment cessation after 2 years of sustained remission — very slow taper of MTX, then prednisolone
• Polycyclic and chronic continuous courses are common — relapse during or after drug cessation requires prompt treatment intensification
• Long-term follow-up continues even in clinical remission — nailfold capillaroscopy, calcinosis monitoring, cardiovascular risk (lipodystrophy, chronic inflammation)

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