VEXAS Syndrome Presenting as Erythema Nodosum and Pancytopenia: Diagnostic Utility of 18 F-FDG PET/CT in Systemic Inflammation.

VEXAS syndrome (Vacuoles, E1 enzyme, X-linked, Auto-inflammatory, Somatic) is a recently identified adult-onset auto-inflammatory disorder caused by somatic mutations in the UBA1 gene. This syndrome can mimic infections, hematologic malignancies, and autoimmune diseases, making diagnosis challenging. We present a case involving a 47-year-old man with hyperthyroidism who experienced prolonged fever, painful nodules, and pancytopenia. Initial evaluations suggested erythema nodosum and vasculitis. An 18 F-FDG PET/CT scan revealed diffuse hypermetabolism in the lungs, bone marrow, spleen, and lower limb muscles, indicating systemic inflammation. A bone marrow biopsy showed vacuolated precursors, and subsequent testing confirmed the presence of a somatic UBA1 mutation, diagnosing him with VEXAS syndrome. This case emphasizes the crucial role of 18 F-FDG PET/CT in evaluating unexplained systemic inflammation and assisting in diagnosing rare auto-inflammatory disorders.