18F-FDG PET/CT in diagnosis and response evaluation in an unusual case of antisynthetase syndrome presenting as pyrexia of unknown origin.

Anti-histidyl (Jo-1) antibodies have been implicated in the pathogenesis of anti-synthetase syndrome (ASS). A case is presented of a 55-year-old male patient presenting with pyrexia of unknown origin and inconclusive routine investigations. (18)F-FDG PET/CT was performed to locate any abnormal focus, which showed increased FDG uptake in the proximal shoulder muscles, as well as lung lesions. Subsequent investigation showed the presence of anti Jo-1 antibody, and diagnosed as an anti-synthetase syndrome. The patient was successfully treated with glucocorticoids and cyclophosphamide, and the response was assessed with symptomatic relief and disappearance of FDG uptake in lung and muscle lesions on post-treatment FDG PET/CT.