18FDG PET/CT: an aid for the early diagnosis of paucisymptomatic polyarteritis nodosa

Dear Editor, We read with great interest the article by Fagart et al. that was published in Rheumatology [1], and we would like to report two other cases. Two male patients aged 62 (P1) and 55 (P2) years, who were referred for persistent fever with a 4-kilogram loss of weight and severe myalgia evolving for 1 month, exhibited a normal physical examination with the exception of bilateral orchi-epididymitis confirmed by ultrasound in the P1. In both cases, biochemical, immunological and microbiological analyses revealed isolated increases in C-reactive protein levels.18F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) showed diffuse heterogeneous hypermetabolism in soft tissues along the peri- and intramuscular arterial tree without subcutaneous hypermetabolism (Fig. 1A and B), producing a marbled appearance similar to Wagyu beef or the cutaneous livedo reticularis seen in polyarteritis nodosa (PAN). Thus, PAN was diagnosed according to ACR criteria for P1 [2] and based on clinical judgement and the absence of an alternative diagnosis after 6 months of follow-up for the P2. The results of FDG PET/CT showing suggestive findings of vasculitis led the clinician to start treatment before obtaining a muscular biopsy given that both patients experienced a rapid deterioration of their general condition. After two months of treatment with steroids and methotrexate 20 mg per week, the patients presented complete clinical and biological remission with the disappearance of FDG PET/CT hypermetabolism (Fig. 1C and D).