What is the treatment for Polymyositis (inflammatory muscle disease)?

Treatment of Polymyositis

The initial treatment for polymyositis should include high-dose corticosteroids (prednisone 1 mg/kg/day up to 60 mg/day) administered concurrently with a steroid-sparing agent such as methotrexate, azathioprine, or mycophenolate mofetil, followed by a tapering course of corticosteroids after 2-4 weeks depending on response. 1

Diagnosis Confirmation

Before initiating treatment, confirm the diagnosis with:

• Elevated muscle enzymes (CK, LDH, AST, ALT)
• Inflammatory markers (ESR, CRP)
• EMG showing myopathic changes
• MRI showing muscle edema
• Muscle biopsy showing endomysial infiltration of mononuclear cells (gold standard)
• Myositis-specific antibodies (including anti-Jo-1)

Treatment Algorithm

First-Line Therapy

1. High-dose corticosteroids:

   • Prednisone 1 mg/kg/day (maximum 60 mg/day) 2, 1
   • Continue for 2-4 weeks at full dose before tapering
   • Taper gradually based on clinical response and CK levels

2. Concurrent steroid-sparing agent (start at the same time as corticosteroids):

   • Methotrexate (15-25 mg weekly)
   • Azathioprine (2-3 mg/kg/day)
   • Mycophenolate mofetil (2-3 g/day)

For Severe or Refractory Disease

If inadequate response to first-line therapy or severe disease presentation:

1. High-dose methylprednisolone pulse therapy (1000 mg IV daily for 3-5 days) 1

2. Additional immunosuppressive options:

   • Intravenous immunoglobulin (IVIG) (2 g/kg divided over 2-5 days) 2, 1
   • Cyclophosphamide (for cases with interstitial lung disease)
   • Rituximab (for refractory cases)
   • Cyclosporine or tacrolimus (particularly effective for cases with interstitial lung disease) 3

3. Plasmapheresis for cases with poor response to corticosteroids or life-threatening situations 2

Monitoring Treatment Response

1. Clinical assessment:

   • Muscle strength (proximal muscles particularly)
   • Functional capacity

2. Laboratory monitoring:

   • CK levels every 4-6 weeks
   • Inflammatory markers (ESR, CRP)
   • Liver function tests and complete blood count (for medication toxicity)

3. Extramuscular manifestations:

   • Pulmonary function tests if interstitial lung disease is present
   • Cardiac evaluation if cardiac involvement is suspected

Special Considerations

Interstitial Lung Disease

• More aggressive immunosuppression is required
• Cyclophosphamide, cyclosporine, or tacrolimus should be considered 3
• Pulmonary function tests and high-resolution CT monitoring

Malignancy Screening

• Complete age-appropriate cancer screening
• Consider more extensive screening in patients with dermatomyositis

Steroid-Related Complications

• Implement bone health measures (calcium, vitamin D, bisphosphonates)
• Monitor for hyperglycemia, hypertension, and weight gain
• Consider PCP prophylaxis in heavily immunosuppressed patients

Common Pitfalls

1. Delayed diagnosis and treatment can lead to irreversible muscle damage 1

2. Inadequate initial immunosuppression - using corticosteroids alone without steroid-sparing agents may lead to higher cumulative steroid doses and associated complications 4

3. Tapering corticosteroids too quickly can result in disease flares

4. Overlooking extramuscular manifestations, particularly interstitial lung disease which can be life-threatening 1

5. Failure to distinguish polymyositis from inclusion body myositis, which is typically resistant to immunosuppressive therapy 5

The treatment approach should be aggressive initially to control inflammation and prevent permanent muscle damage, with careful monitoring for treatment response and medication side effects. Multi-target treatment with glucocorticoids and steroid-sparing agents has shown efficacy in refractory cases 4.