A case report of a 56-year-old man with bilateral epididymo-orchitis, high fever, and disabling lower-limb myalgia in whom whole-body ¹⁸F-FDG PET/CT was used to evaluate a suspected diagnosis of polyarteritis nodosa (PAN) after extensive negative infectious and autoimmune workup.
FDG-PET/CT revealed a bilateral 'ant-farm-like' pattern of irregular uptake along femoral vascular trajectories and fascial planes, supporting a clinical diagnosis of non-severe, non-HBV-associated PAN (Five-Factor Score = 0); treatment with prednisone 30 mg/day plus azathioprine 50 mg twice daily achieved clinical and biochemical response within 2 weeks. Targeted quadriceps biopsy was non-diagnostic, likely due to corticosteroid initiation 12 days prior.
- Single case report; no generalizability. - Biopsy was performed 12 days after corticosteroid initiation and was non-diagnostic, leaving histologic confirmation absent. - The specificity of the 'ant-farm-like' PET pattern for PAN remains under evaluation.
In patients with unexplained fever, lower-limb myalgia, and epididymo-orchitis, the bilateral 'ant-farm-like' FDG-PET/CT pattern along femoral vascular and fascial planes should raise strong suspicion for PAN and can guide biopsy site selection. When biopsy is planned, it should ideally be performed before or very early after corticosteroid initiation to maximize diagnostic yield.
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