Differential Tracer Uptake on FDG PET/CT Unmasking Dual Pathology - Systemic Amyloidosis with Active Tuberculosis

Systemic amyloidosis is an uncommon disorder characterised by extracellular deposition of misfolded protein fibrils, often presenting with nonspecific clinical manifestations and multisystem involvement. Tuberculosis (TB), an endemic infectious disease in developing countries, can coexist with other chronic inflammatory conditions and may pose significant diagnostic challenges on imaging, particularly on 18 F-fluorodeoxyglucose (FDG) positron emission tomography–computed tomography (PET/CT). We report a rare case of concurrent systemic amyloidosis and tuberculous lymphadenitis in a 58-year-old female, highlighting the complementary role of FDG PET/CT in delineating metabolically active infectious foci from relatively hypometabolic infiltrative amyloid deposits. The case underscores the importance of differential metabolic behaviour and guiding site-specific biopsy. Recognition of discordant FDG uptake patterns is essential in TB-endemic regions to avoid misdiagnosis and enable accurate characterisation of concurrent infectious and infiltrative disorders.