Muscular polyarteritis nodosa: a diagnostic and therapeutic challenge.

A healthy man in his early 30s presents with a rare case of muscular polyarteritis nodosa (m-PAN), with fever, severe lower extremity myalgia and systemic inflammatory markers. Initial diagnostic challenges were overcome through repeat MRI, which revealed oedematous changes indicative of myositis, and a definitive muscle biopsy confirming necrotising vasculitis. Initial treatment with corticosteroids reduced inflammation, but persistent symptoms necessitated the use of cyclophosphamide and intravenous immunoglobulin, resulting in gradual symptom resolution. The case emphasises the importance of recognising m-PAN in patients with localised myalgia and inflammation, using MRI to guide biopsies, and initiating prompt immunosuppressive therapy for improved outcomes.