What is the initial treatment for myositis?

Initial Treatment for Myositis

The initial treatment for myositis should be high-dose corticosteroids (prednisone 0.5-1 mg/kg/day, typically 60-80 mg daily) combined with a steroid-sparing immunosuppressive agent such as methotrexate, azathioprine, or mycophenolate mofetil started at disease onset. 1

Diagnostic Workup Before Treatment

Before initiating treatment, a thorough diagnostic workup should include:

• Blood tests for muscle inflammation:

  • Creatine kinase (CK)
  • Transaminases (AST, ALT)
  • Lactate dehydrogenase (LDH)
  • Aldolase
  • Troponin (to evaluate myocardial involvement)
  • Inflammatory markers (ESR, CRP)
  • Autoimmune myositis panel

• Additional testing as needed:

  • Electromyography (EMG)
  • MRI of affected proximal muscles
  • Muscle biopsy (if diagnosis uncertain)
  • Urinalysis (to check for rhabdomyolysis)
  • Paraneoplastic autoantibody testing 1

Treatment Algorithm Based on Severity

Grade 1 (Mild weakness with or without pain)

• Continue regular activities
• If CK/aldolase elevated with muscle weakness:
  • Start prednisone at 0.5 mg/kg/day
• Provide analgesia with acetaminophen or NSAIDs if no contraindications
• Consider holding statins if patient is taking them 1

Grade 2 (Moderate weakness with or without pain)

• Temporarily hold immune checkpoint inhibitors if relevant
• Refer to rheumatologist or neurologist
• If CK is elevated (3× ULN or more):
  • Initiate prednisone 0.5-1 mg/kg/day
• Provide NSAIDs as needed for pain 1

Grade 3-4 (Severe weakness with or without pain)

• Consider hospitalization for severe weakness affecting mobility, respiration, or causing dysphagia
• Urgent referral to rheumatologist and/or neurologist
• Initiate prednisone 1 mg/kg/day or equivalent
• For severe cases, consider IV methylprednisolone 1-2 mg/kg or higher-dose bolus
• Consider plasmapheresis for acute or severe disease
• Consider IVIG therapy (noting slower onset of action) 1

Corticosteroid Tapering Protocol

After 2-4 weeks of high-dose corticosteroids, begin tapering based on clinical response:

1. Reduce by 10 mg every 2 weeks until reaching 30 mg/day
2. Then reduce by 5 mg every 2 weeks until reaching 20 mg/day
3. Then reduce by 2.5 mg every 2 weeks until completed
4. At 10 mg/day, may slow taper to 1 mg every 2-4 weeks until completed 1

Steroid-Sparing Agents

Concurrent with corticosteroids, initiate one of the following immunosuppressive drugs:

Methotrexate

• Start at 25-50 mg/week with increments of 25-50 mg/week
• Target dose: 15-20 mg/m²/week (maximum 40 mg/week)
• Preferably administered subcutaneously 1, 2

Azathioprine

• Check thiopurine methyltransferase level before starting
• Start at 25-50 mg/day
• Target dose: 2 mg/kg of ideal body weight in divided doses
• Common side effects: nausea, loose stools, fever, liver toxicity 1

Mycophenolate Mofetil

• Particularly useful for persistent muscle and skin disease
• May be effective for cases with calcinosis 2

Treatment for Refractory Disease

If inadequate response to initial therapy after 4 weeks or worsening symptoms:

1. Consider IVIG therapy (1 g/kg divided over 1-2 days, repeated monthly)
2. Consider rituximab, particularly for refractory cases
3. Consider other immunosuppressants:
   • Cyclophosphamide (0.6-1.0 g/m² IV every 4 weeks for 3-6 months)
   • Cyclosporine A (3.0-3.5 mg/kg daily)
   • Tacrolimus
   • TNF-α or IL-6 receptor inhibitors 1, 2

Monitoring During Treatment

• Regular assessment of muscle enzymes (CK, LDH, AST)
• Monitor inflammatory markers (ESR, CRP)
• For specific medications:
  • Methotrexate: CBC, liver function tests
  • Azathioprine: CBC, liver function tests
  • Cyclophosphamide: WBC count 8-14 days after infusion
  • Hydroxychloroquine: baseline ECG and ophthalmologic monitoring 2

Important Considerations

• Early initiation of therapy is associated with better functional outcomes 3
• Prolonged administration of high-dose corticosteroids alone should be avoided 4
• Steroid-related myopathy and osteoporosis are particularly relevant side effects in myositis patients 3
• For patients with dermatomyositis, sun protection is essential to prevent skin flares 2
• A safe and appropriate exercise program monitored by a physiotherapist is a critical component of care 2

The combination of high-dose corticosteroids with early initiation of steroid-sparing agents represents the current standard of care for myositis, with treatment modifications based on disease severity and response to therapy.