A rare inflammatory myopathy of childhood, similar to adult dermatomyositis but with additional features such as calcinosis and more prominent cutaneous involvement.
Represents a systemic autoimmune vasculopathy with muscle, skin, and sometimes pulmonary involvement.

📊 Incidence

Occurs in 2–3 per million children per year.
Average age of onset: ~7 years.
More common in Caucasian children.

🧬 Aetiology & Pathogenesis

Genetic risk: TNF-α 308A allele linked with severe disease, calcinosis, and ulceration.
Immune dysregulation: MHC-I and β2-microglobulin overexpressed in affected muscle.
Triggers: Infections, UV exposure, epigenetic and post-meiotic events.

🧾 Diagnostic Criteria

Symmetrical proximal muscle weakness – hips, shoulders, thighs, neck.
Characteristic skin manifestations:
- Heliotrope rash: Purple eyelid discoloration ± periorbital oedema.
- Gottron’s papules: Raised erythematous or violaceous papules over knuckles, elbows, knees.
Raised muscle enzymes: CK, aldolase, AST, ALT, LDH.
Electromyography: Myopathic changes with irritability and denervation.
Muscle biopsy: Perifascicular atrophy, fibre degeneration/regeneration, capillary loss.

🩺 Clinical Presentation

Systemic: Fever, anorexia, fatigue, lymphadenopathy, sleep disturbance.
Skin:
- Gottron’s papules
- Heliotrope rash ± periorbital oedema
- Periungual telangiectasia
- Generalised erythema & depigmentation over joints
Muscle weakness: Proximal > distal, difficulty rising, climbing stairs, lifting arms.
Mechanic’s hands: Hyperkeratotic, fissured skin on hands – associated with ILD risk.

🔬 Investigations

Bloods: FBC, U&E, LFT, CRP, ESR, autoantibodies.
Muscle enzymes: CK, LDH elevated in active disease.
EMG: Irritability, denervation.
Muscle biopsy: Diagnostic gold standard (but invasive).
MRI: Non-invasive, highlights muscle oedema (T2/STIR sequences).
Nailfold capillaroscopy: Correlates with disease activity.

💊 Management (Specialist MDT Care)

Multidisciplinary team: paediatric rheumatology, dermatology, physiotherapy, family support.
Corticosteroids: First-line (oral prednisolone or IV methylprednisolone).
Methotrexate: Often added early to reduce steroid burden.
Refractory disease: IVIG, mycophenolate, ciclosporin, rituximab.
Supportive care: Physiotherapy, skin care (sun protection), nutritional support.

📈 Prognosis

Mortality has fallen markedly with modern treatment.
~50% of children still experience long-term impairment or functional disability.
Calcinosis and chronic weakness are major morbidity causes.

📚 References

Juvenile Dermatomyositis – ResearchGate

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Juvenile Dermatomyositis

📖 About Juvenile Dermatomyositis (JDM)