What is the initial treatment for a patient diagnosed with Polymyositis (inflammatory muscle disease)?

Initial Treatment for Polymyositis

The initial treatment for polymyositis should be high-dose oral 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. 1

Corticosteroid Therapy

Initial Dosing

• Begin with prednisone at 0.5-1 mg/kg/day (typically 60-80 mg/day) as a single daily dose 1
• Continue this high dose for 2-4 weeks depending on clinical response 1
• For severe cases with significant weakness, consider IV methylprednisolone 1-2 mg/kg or higher dose bolus 1

Tapering Schedule

• After 2-4 weeks of high-dose therapy, begin tapering by 10 mg every 2 weeks until reaching 30 mg/day 1
• Then slow the taper to 5 mg every 2 weeks until reaching 20 mg/day 1
• Further slow to 2.5 mg every 2 weeks until completed 1
• At 10 mg/day, may need to slow further to 1 mg every 2-4 weeks 1

Concurrent Steroid-Sparing Agent

Start one of the following immunosuppressive agents concurrently with corticosteroids:

Methotrexate

• First-line steroid-sparing agent for most patients 2
• Start at 25-50 mg/week with increments of 25-50 mg/week until reaching target dose 1
• May take 3-6 months to reach full efficacy 1
• Caution: Avoid in patients with interstitial lung disease or anti-Jo-1 antibodies 3

Azathioprine

• Alternative to methotrexate, especially in patients with lung involvement 3
• Target dose: 2 mg/kg of ideal body weight in divided doses 1
• Check thiopurine methyltransferase level before starting to screen for enzyme deficiency 1
• Start at lower doses and gradually increase to target 1

Mycophenolate Mofetil

• Alternative option when methotrexate or azathioprine are not tolerated 1
• Particularly useful in patients with interstitial lung disease 1

Monitoring Response

• Monitor muscle strength clinically
• Track creatine kinase (CK) levels, but note that normalization of CK does not always equate to disease control 4
• Consider follow-up MRI to assess muscle inflammation 1
• Evaluate for extramuscular manifestations (skin rash, interstitial lung disease)

Management of Refractory Disease

For patients who fail to respond to initial therapy:

1. Verify diagnosis with repeat muscle biopsy 2
2. Consider intravenous immunoglobulin (IVIG) 2, 3
3. For persistent disease, consider rituximab 2
4. Important: Avoid TNF-α antagonists as they may exacerbate interstitial lung disease and myositis 2

Special Considerations

• Patients with severe weakness affecting mobility, respiration, or swallowing may require hospitalization 1
• Consider urgent referral to rheumatology and/or neurology for severe cases 1
• Physical therapy should be incorporated into treatment plan to maintain muscle mass and function
• Screen for malignancy in adult patients with dermatomyositis (25% association) and polymyositis (10-15% association) 1

Common Pitfalls

• Tapering corticosteroids too quickly can lead to disease flares
• Failing to start a steroid-sparing agent concurrently with corticosteroids
• Overlooking the need for age-appropriate cancer screening
• Using TNF-α inhibitors, which can worsen disease 2
• Relying solely on CK levels to guide therapy without clinical correlation 4

The treatment approach should be adjusted based on disease severity, with more aggressive therapy for patients with severe weakness or extramuscular manifestations.