Muscular polyarteritis nodosa detected by FDG-PET/CT

Abstract

A 56-year-old woman presented with high-grade fever and myalgia of the lower extremity. Physical examination showed muscle tenderness of the lower extremity. Laboratory examinations revealed an elevated CRP level of 8.5 mg/dL, an erythrocyte sedimentation rate of 126 mm/h, and white blood cells 18.4 × 10⁹/L, but normal a creatine phosphokinase level of 42 U/L. ANCA and ANA were all negative. Hepatic and renal functions were normal. Human leukocyte antigen typing demonstrated positive A2, A31, B46, and B61 antigens. 18F-FDG-PET demonstrated medium-sized vessels with increased FDG uptake (Figure 1A, arrowheads), and axial views of fusion PET/CT images with color coding showed medium-sized vascular inflammation with increased FDG uptake (SUVmax 2.8) in superficial femoral artery, lateral femoral circumflex artery (Figure 1B–D, arrowheads), peroneal artery, and posterior tibial artery (Figure 1E,F, arrowheads), indicating vasculitis in lower extremity. MRI (fat-suppressed T2-weighted image) revealed quadriceps femoris, adductor, and gastrocnemial muscular inflammation (Figure 1G, black in white arrow). Biopsy specimen that was percutaneously taken from gastrocnemial muscle demonstrated medium-sized necrotizing arteritis (Figure 1I, white arrow) and its inflammatory effect on the muscle (Figure 1I, black in white arrow). The patient was diagnosed as having muscular polyarteritis nodosa (PAN). Her symptoms and laboratory findings were completely improved by treatments with prednisolone and azathioprine. Furthermore, MRI findings of gastrocnemial muscle also improved (Figure 1H). Muscular connective tissue uptake on FDG-PET/CT could guide the diagnosis toward PAN.¹ This case highlights the value of PET-CT in the diagnosis of muscular PAN.

Taniguchi Y and Yamamoto H equally contributed to this manuscript.

The authors received no funding for this study.

The authors declare no conflict of interest.