What is the recommended steroid dosage and treatment regimen for a patient experiencing a polymyositis exacerbation?

Steroid Treatment for Polymyositis Exacerbation

For a polymyositis exacerbation, initiate high-dose oral prednisone at 1 mg/kg/day (typically 60-80 mg/day for most adults) combined with methotrexate 15-20 mg/m² weekly from the outset, as this combination approach reduces long-term steroid exposure and improves functional outcomes. 1, 2, 3

Initial Steroid Dosing

Oral prednisone is the steroid of choice at 1 mg/kg/day as a single morning dose. 1, 2 This translates to approximately 60-80 mg daily for most adults. 1

• For severe exacerbations with significant weakness limiting mobility, dysphagia, or respiratory compromise, use intravenous methylprednisolone 1-2 mg/kg/day instead of oral therapy. 1
• Single daily dosing in the morning is preferred to minimize hypothalamic-pituitary-adrenal axis suppression. 4

Concurrent Steroid-Sparing Agent

Start methotrexate simultaneously with corticosteroids, not as a later addition. 1, 2 This is critical because:

• Methotrexate at 15-20 mg/m² weekly (maximum 40 mg/week) reduces cumulative steroid exposure and improves long-term functional disability. 1, 3
• Subcutaneous administration is preferred over oral for better bioavailability. 1
• The therapeutic effect appears within 8 weeks. 2
• Long-term follow-up demonstrates superior functional outcomes compared to prednisone monotherapy. 3

Steroid Tapering Protocol

Begin tapering only after clinical improvement is evident, typically after 2-4 weeks of high-dose therapy. 1, 4

The recommended taper schedule is: 4

• Weeks 1-4: Reduce by 10 mg every 2 weeks until reaching 30 mg/day
• Weeks 5-8: Reduce by 5 mg every 2 weeks until reaching 20 mg/day
• Weeks 9-12: Reduce by 2.5 mg every 2 weeks until reaching 10 mg/day
• After reaching 10 mg/day: Slow to 1 mg every 2-4 weeks until discontinuation

The most common error is tapering too quickly, which leads to disease flare. 4 The entire taper typically takes 6-12 months. 5

Monitoring During Treatment

Check the following at each visit (every 2-4 weeks initially): 1

• Creatine kinase (CK) levels - though normalization does not always equate to disease control 6
• Manual muscle testing of proximal muscle groups
• Functional assessment (ability to rise from chair, lift arms overhead)
• Signs of steroid-related adverse effects

Management of Inadequate Response

If no improvement occurs within 8-12 weeks despite adequate steroid and methotrexate therapy, add intravenous immunoglobulin (IVIG). 1, 2

• IVIG is particularly effective for refractory disease, though onset of action is slower than other agents. 1
• Before escalating therapy, strongly consider repeat muscle biopsy to exclude alternative diagnoses such as inclusion body myositis, necrotizing myopathy, or statin-induced myopathy. 2

For truly refractory cases after confirming the diagnosis: 1, 2

• Mycophenolate mofetil can be added or substituted for methotrexate
• Rituximab is effective for primary myositis but may take up to 26 weeks to work 1
• Avoid TNF-α antagonists - these can exacerbate myositis and increase infection risk 2

Critical Pitfalls to Avoid

Do not use prednisone monotherapy without a steroid-sparing agent from the start. 1, 3 Historical data show this approach requires higher cumulative steroid doses and results in worse functional outcomes. 3

Do not stop statins without considering the diagnosis. 1 While statins can cause myopathy, stopping them in true polymyositis will not resolve the condition and delays appropriate immunosuppression.

Do not equate CK normalization with disease control. 6 Clinical strength assessment is more reliable than CK levels alone for guiding therapy adjustments.

Special Considerations for Severe Disease

For grade 3-4 severity (severe weakness limiting self-care, dysphagia, or respiratory involvement): 1

• Hospitalize the patient immediately
• Use IV methylprednisolone 1-2 mg/kg/day rather than oral prednisone
• Consider plasmapheresis for acute severe disease with rheumatology guidance 1
• Note that plasmapheresis immediately after IVIG will remove the immunoglobulin 1
• Urgent rheumatology and/or neurology consultation is mandatory 1

Adrenal Insufficiency Prevention

Any patient receiving >7.5 mg daily for >3 weeks requires stress-dose steroids during acute illness. 4

• For patients on 10 mg prednisone daily: increase to hydrocortisone 50 mg twice daily for 3 days during acute stress 4
• Educate patients on stress dosing and consider a medical alert bracelet 4