What is the recommended treatment for myositis in children?

Treatment of Myositis in Children

For children with juvenile dermatomyositis (JDM), the recommended initial treatment is high-dose corticosteroids (2 mg/kg/day up to maximum 60 mg/day) combined with methotrexate (15-20 mg/m²/week) started at disease onset. 1

Initial Treatment Approach

First-line Therapy

• Corticosteroids:

  • Dosage: 2 mg/kg/day (maximum 60 mg/day)
  • Begin tapering after 2-4 weeks depending on clinical response
  • Taper schedule: Reduce by 10-20% of current dose every 4 weeks once reaching 0.5 mg/kg 1

• Methotrexate (started concurrently with corticosteroids):

  • Dosage: 15-20 mg/m²/week (maximum 40 mg/week)
  • Preferably administered subcutaneously 1
  • Key component of consensus treatment protocols

Sun Protection

• Routine use of sunblock on sun-exposed areas
• Wide-brimmed hats and long-sleeved shirts
• Avoidance of UV rays to prevent skin flares 1

Physical Therapy

• Safe and appropriate exercise program monitored by a physiotherapist
• Critical component of multidisciplinary care 1

Management of Severe or Refractory Disease

For patients with severe disease manifestations or inadequate response to initial therapy:

1. Intravenous Methylprednisolone (IVMP):

   • Dosage: 30 mg/kg/day (maximum 1 g/day) for 3 days 1
   • Consider within first 12 weeks if inadequate response to initial therapy

2. Intravenous Immunoglobulin (IVIG):

   • Dosage: 1 g/kg divided over 1-2 days, repeated monthly for 1-6 months
   • Particularly useful when skin features are prominent 1
   • For children with body surface area ≤1.5 m²: 575 mg/m² per infusion
   • For children with body surface area >1.5 m²: 750 mg/m² up to 1 g per infusion 1

3. Mycophenolate Mofetil (MMF):

   • Useful for persistent muscle and skin disease, including calcinosis 1

4. For severe refractory disease:

   • Cyclophosphamide: 0.6-1.0 g/m² IV every 4 weeks for 3-6 months (rarely extended to 12 months) 1
   • Rituximab: For refractory cases 1
   • Cyclosporine A: 3.0-3.5 mg/kg daily (reserved for severe, refractory cases) 1

Management of Skin Disease

• Topical treatments:

  • Topical corticosteroids of varying strengths
  • Topical tacrolimus (0.1%) for localized skin disease 1

• Systemic approach:

  • Ongoing skin disease reflects ongoing systemic disease and should be treated with increased systemic immunosuppression 1
  • Hydroxychloroquine: 5 mg/kg/day (typically 200 mg twice daily) primarily for cutaneous manifestations 1

Monitoring and Follow-up

• Regular assessment of muscle enzymes (CPK, LDH, AST) for disease monitoring, recognizing they may be normal despite active disease 1
• Monitor for calcinosis, which affects approximately 3% of patients with appropriate treatment 2
• For patients on cyclophosphamide: Monitor white blood cell count 8-14 days after infusion (avoid nadir <3.0 x 10⁹/L) 1
• For patients on hydroxychloroquine: Baseline electrocardiogram and ophthalmologic monitoring 1

Recent Developments

Recent evidence suggests that reduced glucocorticoid dosing (median 0.85 mg/kg/day) with early introduction of steroid-sparing agents may be comparably effective in achieving favorable outcomes while minimizing steroid-related side effects 2. This approach resulted in myositis control in a median of 7.1 months and cutaneous disease control in a median of 16.7 months 2.

Important Considerations

• Early diagnosis and treatment initiation is associated with better functional outcomes 3
• Always consider secondary causes of myositis (infections, drugs, malignancies) which may require specific therapies beyond immunomodulatory treatment 4, 5
• Monitor closely for glucocorticoid-related adverse effects, particularly steroid-induced myopathy and osteoporosis 3
• Maintain high index of suspicion for JC virus reactivation in patients presenting with central nervous system abnormalities 1

The multidisciplinary team should include a physiotherapist and specialist nurse actively involved in the care of children with JDM 1.