Viral Myositis and CPK Elevation

Diagnostic Considerations

• The American College of Physicians, as noted in the Mayo Clinic Proceedings, suggests that immune-mediated necrotizing myopathy (IMNM) can present with CPK elevations greater than 10 times the upper limit of normal, which must be differentiated from viral myositis through autoantibody testing and clinical context 1
• In polymyalgia-like syndromes, CPK levels should remain within normal limits, serving as a key differentiating feature from true myositis, according to the American Society of Clinical Oncology 2, 3

Laboratory Testing

• The European League Against Rheumatism recommends that multiple muscle enzymes should be measured at diagnosis (CPK, AST, ALT, LDH, aldolase) as one may be elevated when CPK is normal or only mildly elevated 4