The role of PET/CT scan in addressing autoinflammatory diseases; A case report of a young man presenting with fever, splenomegaly and exanthem.

Objective: Adult-onset Still's disease (AOSD) is an uncommon autoinflammatory syndrome characterized by quotidian fever, arthritis, evanescent exanthem and splenomegaly. Lymphadenopathy is present in about a half of patients; it is usually symmetrical with the cervical area being most commonly involved. When constitutional symptoms are present, an extensive work-up should be performed in order to exclude hematological malignancies, such as lymphoma.

Subjects and methods: A 38-year-old male is presented due to fatigue and high-grade fever that first appeared a month ago. He did also refer night sweats, arthralgias and an evanescent erythema on the trunk and anterior thigh area. Serology testing for bacteria and viruses as well as autoimmune rheumatic diseases was requested. Whole body computed tomography (CT) scan was ordered and displayed a marginal lymph node in the right hilum and smaller ones in the axillary region. Positron emission tomography/CT (PET/CT) with fluorine-18-fluoro-deoxy-glucose (¹⁸F-FDG) showed hypermetabolic lymph nodes, with the right upper internal jugular lymph node being the most dominant, as well as diffusely increased ¹⁸F-FDG uptake by bone marrow and spleen, posing in the differential diagnosis a neoplastic disease of the hematopoietic tissues.

Results: Further laboratory testing showed high ferritin levels. It was decided to procced with biopsy of the aforementioned hypermetabolic internal jugular lymph node and bone marrow. Histopathological examination did show hyperreactivity and no malignant cells neither in the lymph node nor in the bone marrow.

Conclusion: Adult-onset Still's disease is a rare disorder and it is a diagnosis of exclusion. High-grade fever along with arthralgias, splenomegaly, high serum ferritin levels and the presence of exanthem should pose high in the differential the AOSD. In this case, PET/CT guided the anatomical location for lymph node biopsy in order to differentiate AOSD from lymphoma. The dissociated increased ¹⁸F-FDG uptake from the cervical and axillary lymph nodes is characteristic of AOSD.