What is the recommended initial treatment for polymyositis in an adult?

Polymyositis Treatment

Begin prednisone at 0.5-1 mg/kg/day (typically 60-80 mg daily as a single dose) for 2-4 weeks, and concurrently initiate a steroid-sparing immunosuppressive agent from day one—never use corticosteroid monotherapy, as it fails in 86% of cases. 1, 2

Initial Treatment Protocol

The cornerstone of polymyositis management involves dual therapy from the outset:

Corticosteroid Component

• Start prednisone at 0.5-1 mg/kg/day as a single daily dose 3, 1, 2
• Use higher doses (closer to 1 mg/kg) for patients at high risk of relapse and low risk of adverse events 2
• Use lower doses (closer to 0.5 mg/kg) for patients with diabetes, osteoporosis, or glaucoma 2
• Continue this initial dose for 2-4 weeks before beginning taper 1, 2

Mandatory Concurrent Steroid-Sparing Agent (Choose One)

Methotrexate (First-line for most patients):

• Start at 15 mg orally once weekly with 1 mg/day folic acid supplementation 3, 2
• Increase to target dose of 25 mg weekly within 3-6 months 3, 2
• Screen for hepatitis B/C and obtain baseline liver function tests before initiating 3, 2
• Counsel patients to avoid excessive alcohol use 3
• Women of childbearing potential require reliable contraception (teratogenic) 3, 2
• Avoid in patients with significant interstitial lung disease 3

Azathioprine (Preferred for interstitial lung disease or pregnancy planning):

• Check thiopurine methyltransferase level before initiating to screen for enzyme deficiency 3
• Target dose: 2 mg/kg ideal body weight in divided doses 3, 2
• Start at 25-50 mg/week with increments of 25-50 mg/week until goal dosage is reached 3

Mycophenolate mofetil (Preferred for severe dermatomyositis skin disease):

• Start at 500 mg twice daily 3, 2
• Increase by 500 mg/week until reaching 1000 mg twice daily 3

Systematic Corticosteroid Tapering Schedule

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

• 60 mg/day → 40 mg/day (every 2 weeks) 3, 2
• 40 mg/day → 30 mg/day (every 2 weeks) 3, 2
• 30 mg/day → 25 mg/day (every 2 weeks) 3, 2
• 25 mg/day → 20 mg/day (every 2 weeks) 3, 2
• 20 mg/day → 17.5 mg/day (every 2 weeks) 3
• 17.5 mg/day → 15 mg/day (every 2 weeks) 3
• 15 mg/day → 12.5 mg/day (every 2 weeks) 3
• 12.5 mg/day → 10 mg/day (every 2 weeks) 3
• 10 mg/day → 7.5 mg/day (every 2 weeks) 3
• 7.5 mg/day → 5 mg/day (every 2 weeks) 3
• 5 mg/day → 2.5 mg/day (every 2 weeks) 3

Critical principle: Continue the initial corticosteroid dose until or after the serum creatine kinase has normalized 4. Tapering when CK is elevated frequently results in further CK increase and clinical relapse 4.

Treatment for Severe Disease

For patients with severe weakness, dysphagia, respiratory muscle involvement, or extensive extramuscular organ involvement:

• Add IV methylprednisolone 10-20 mg/kg (250-1000 mg) for 1-5 consecutive days 1, 2
• Consider IVIG at 1-2 g/kg ideal body weight over 2 consecutive days (1 g/kg each day) 2
• Consider additional agents such as cyclophosphamide or cyclosporine for refractory disease 1, 2

Monitoring Requirements

• Monitor creatine kinase levels regularly—achieving CK within the low normal range predicts prolonged biochemical remission 4
• A rise of CK within the normal range signals subsequent biochemical and clinical relapse 4
• Assess muscle strength and functional capacity at each visit 2
• Consider MRI with T2-weighted and fat suppression sequences to assess muscle inflammation 1, 2
• Screen for steroid-related complications: obtain DEXA scan for bone health, prescribe calcium and vitamin D supplements, add bisphosphonate if osteoporosis present 2

Critical Pitfalls to Avoid

Never use corticosteroid monotherapy—it fails in 86% of cases 1, 2. The evidence is unequivocal that steroid-sparing agents must be initiated from day one, not after corticosteroid failure 2.

Never continue high-dose corticosteroids beyond 2-4 weeks without beginning taper—this increases morbidity (including steroid myopathy) without improving outcomes 2, 5. Steroid myopathy can paradoxically worsen muscle weakness and disability, particularly in elderly patients 5.

Never taper corticosteroids when CK is elevated—this frequently results in further CK increase and clinical relapse 4. Wait until CK normalizes before initiating taper 4.

Never delay initiation of steroid-sparing agents—start on day one, not after corticosteroid failure 2. The combination approach from the outset has been shown to reduce hospitalization periods and improve outcomes 6.

Evidence Quality Note

The most recent and highest quality evidence comes from the 2025 Praxis Medical Insights summaries 1, 2, which synthesize recommendations from the American College of Physicians and Mayo Clinic. These guidelines emphasize the critical importance of dual therapy from day one, which represents a significant evolution from older approaches that used corticosteroid monotherapy. The 2013 Mayo Clinic Proceedings guideline 3 provides detailed practical implementation guidance that remains highly relevant. Research evidence consistently demonstrates that lower initial corticosteroid doses (when combined with steroid-sparing agents) can achieve comparable functional outcomes with reduced treatment-related disability 7, 6.