What is the treatment for post-viral myositis?

Treatment of Post-Viral Myositis

Post-viral myositis is typically a self-limited condition requiring only supportive care with acetaminophen or NSAIDs for symptom relief, with corticosteroids reserved for severe cases with significant weakness or elevated creatine kinase levels. 1, 2

Initial Assessment and Risk Stratification

The critical first step is distinguishing between benign viral myositis (pain without weakness) and true inflammatory myositis (pain with weakness), as this fundamentally changes management 1:

• Examine for muscle weakness, not just pain - weakness in proximal muscles (difficulty standing, lifting arms) indicates true myositis requiring more aggressive treatment 3
• Check creatine kinase (CK) levels - markedly elevated CK (>3× ULN) suggests inflammatory myositis rather than simple myalgia 3, 1
• Assess for cardiac involvement - obtain troponin and ECG immediately, as myocardial involvement dramatically changes prognosis and requires aggressive immunosuppression 3, 1
• Screen for rhabdomyolysis - urinalysis for myoglobinuria is essential, as this complication can be life-threatening 1, 4

Treatment Algorithm Based on Severity

Mild Cases (Pain Without Significant Weakness, Normal or Mildly Elevated CK)

Continue normal activities with symptomatic treatment only 1, 2:

• Acetaminophen or NSAIDs for analgesia if no contraindications 3, 1
• Clinical follow-up to monitor for progression 2, 4
• No corticosteroids needed for simple myalgia 1

This approach is appropriate for the typical benign acute viral myositis seen in children, which is self-limiting and resolves within days to weeks 2, 4.

Moderate Cases (Moderate Weakness Limiting Daily Activities, CK ≥3× ULN)

Initiate prednisone 0.5-1 mg/kg/day and refer to rheumatology or neurology 3:

• Hold any potential causative medications (statins, immune checkpoint inhibitors if applicable) 3
• NSAIDs for additional symptom control 3
• Monitor CK levels serially to assess response 1
• Consider EMG or MRI if diagnosis uncertain or symptoms persist 3

Severe Cases (Severe Weakness Limiting Self-Care, Rhabdomyolysis, or Cardiac Involvement)

Hospitalize immediately and initiate high-dose corticosteroids 3:

• Prednisone 1 mg/kg/day orally, or methylprednisolone 1-2 mg/kg IV for severe compromise 3
• Urgent rheumatology and/or neurology consultation 3
• For refractory cases or life-threatening presentations, consider plasmapheresis - this is preferred over IVIG for acute severe disease due to faster onset 3
• IVIG can be added but has slower onset; avoid plasmapheresis immediately after IVIG as it removes immunoglobulin 3

Additional Laboratory Workup

Beyond CK, obtain the following to guide management 3, 1:

• Aldolase, AST, ALT, LDH (additional muscle inflammation markers) 3, 1
• ESR and CRP (inflammatory markers) 3, 1
• Troponin, ECG, consider echocardiogram or cardiac MRI if any cardiac symptoms 3, 1
• Autoantibody testing (anti-AChR, anti-striational antibodies) if myasthenia gravis suspected 3

Critical Pitfalls to Avoid

Do not assume all CK elevations require corticosteroids - exercise-induced muscle damage can produce CK levels exceeding 10,000 U/L without requiring treatment 1. The presence of weakness, not just elevated CK, should guide corticosteroid initiation.

Always evaluate for cardiac involvement - myocardial involvement has high mortality and requires permanent discontinuation of any causative agents plus aggressive immunosuppression 1. Missing this can be fatal 3.

Do not confuse polymyalgia-like syndrome with true myositis - patients with severe myalgia and fatigue but normal CK and no true weakness have a different condition requiring different management 3.

Refractory or Persistent Cases

If symptoms persist despite corticosteroids or CK levels do not normalize after 2 weeks 3:

• Add steroid-sparing immunosuppressants: methotrexate, azathioprine, or mycophenolate mofetil for maintenance 3, 1
• Consider biologic agents (rituximab, TNF-α or IL-6 antagonists) for severe refractory disease 3
• IVIG therapy can be beneficial, particularly for severe cases 3, 1

Prognosis and Follow-Up

Benign viral myositis in children typically resolves completely within days to weeks without sequelae 2, 4. However, adult cases or those with significant CK elevation require closer monitoring for potential progression to rhabdomyolysis 5, 4. Serial CK measurements should continue until normalization 1.