What are the treatment options for inflammatory myopathy?

Treatment of Inflammatory Myopathy

Start high-dose prednisone (0.5-1 mg/kg/day, typically 60-80 mg daily) immediately concurrent with a steroid-sparing immunosuppressive agent from day one—never use corticosteroid monotherapy as it fails in 86% of inflammatory myopathy cases. 1, 2, 3

Initial Corticosteroid Regimen

• Administer prednisone 0.5-1 mg/kg/day as a single daily dose for 2-4 weeks before beginning taper. 1, 2, 3
• Use doses closer to 1 mg/kg for patients at high risk of relapse and low risk of steroid complications. 1, 3
• Use doses closer to 0.5 mg/kg for patients with diabetes, osteoporosis, or glaucoma. 1, 3
• For severe weakness, dysphagia, or respiratory muscle involvement, add IV methylprednisolone 10-20 mg/kg (250-1000 mg) for 1-5 consecutive days. 1, 2, 3

Mandatory Concurrent Steroid-Sparing Agent (Start Day One)

First-line options:

• Methotrexate: Start 15 mg orally once weekly with 1 mg/day folic acid, increase to target dose of 25 mg weekly within 3-6 months—preferred for most patients without lung disease. 1, 2, 3
• Azathioprine: Target dose 2 mg/kg ideal body weight after checking thiopurine methyltransferase level—preferred for interstitial lung disease or pregnancy planning. 1, 2, 3
• Mycophenolate mofetil: Start 500 mg twice daily—preferred for severe dermatomyositis skin disease or IIM-associated interstitial lung disease. 2, 3

Critical timing: These agents take 3-6 months to reach full efficacy, which is why they must be started immediately, not after corticosteroid failure. 1, 2

Systematic Prednisone Taper

Begin tapering after 2-4 weeks based on clinical response: 1, 2, 3

• 60 mg → 40 mg (every 2 weeks)
• 40 mg → 30 mg (every 2 weeks)
• 30 mg → 25 mg (every 2 weeks)
• 25 mg → 20 mg (every 2 weeks)
• Below 20 mg: slow to 2.5 mg decrements every 2 weeks 2

Never continue high-dose corticosteroids beyond 2-4 weeks—this increases morbidity without improving outcomes. 1, 3

Treatment for Severe or Refractory Disease

Intravenous immunoglobulin (IVIG):

• Dose: 1-2 g/kg ideal body weight over 2 consecutive days (1 g/kg each day) 3
• Indications: dysphagia, notable weight loss, severe rash, weakness, or steroid-resistant disease 2, 3
• The American College of Rheumatology supports IVIG based on controlled trial evidence in dermatomyositis 2, 4, 5

Rituximab:

• Two 1000-mg doses given 2 weeks apart for adults 3
• Reserved for refractory disease not controlled with first-line agents 2, 3, 5

Cyclophosphamide:

• Infusions every 4 weeks for 3-6 months (may extend to 12 months) 3
• Indicated for severe interstitial lung disease or refractory disease 2, 3

Cyclosporine/Tacrolimus:

• Reserved for severe, refractory disease due to serious adverse effects including hypertension and renal insufficiency 3, 5

Disease-Specific Considerations

Anti-HMGCR-associated myopathy:

• Requires aggressive combination therapy from the outset—rarely responds to corticosteroids alone 1, 3
• Never attempt corticosteroid monotherapy in this subtype 1

Inclusion body myositis:

• Generally resistant to standard immunotherapy, but a trial of prednisone with methotrexate is reasonable for newly diagnosed patients 3, 6, 7
• Most patients become unresponsive and disease progresses despite treatment 5

Juvenile dermatomyositis:

• Prednisone 2 mg/kg/day (maximum 60 mg/day) 2, 3
• Subcutaneous methotrexate 15 mg/m² once weekly from treatment onset 2, 3

Monitoring Treatment Response

Track these parameters at regular intervals: 1, 2, 3

• Muscle strength testing and creatine kinase levels
• Functional capacity and activities of daily living
• MRI with T2-weighted and fat suppression sequences to assess muscle inflammation
• Novel biomarkers such as interleukin-6 and type 1 interferon-regulated genes 2

Prevention of Treatment Complications

Mandatory monitoring and prophylaxis: 2, 3

• Bone health: DEXA scan, calcium and vitamin D supplements, add bisphosphonate if osteoporosis present
• Pneumocystis prophylaxis when using multiple immunosuppressants
• Update vaccines before starting immunosuppressants
• Screen for hepatitis B/C and baseline liver function tests before methotrexate 3
• Women of childbearing potential require reliable contraception when taking methotrexate (teratogenic) 3

Critical Pitfalls to Avoid

Three absolute contraindications to common practice errors: 1, 3

1. Never use corticosteroid monotherapy—it fails in 86% of cases
2. Never delay initiation of steroid-sparing agents—start on day one, not after corticosteroid failure
3. Never continue high-dose corticosteroids beyond 2-4 weeks—increases morbidity without improving outcomes