Abstract
Erdheim‒Chester disease (ECD) is a rare non-Langerhans' cell histiocytic proliferative disorder of unknown origin with multisystemic predilection. It commonly affects adults in the fifth-seventh decades of life, with male preponderance, and has nonspecific clinical manifestations. Presence of characteristic radiological findings and demonstration of CD68 positive xanthogranulomatous infiltrates in histology clinches the diagnosis. Nevertheless, being a nonmalignant condition, it might be fatal due to multiorgan dysfunction. Hence, timely diagnosis and initiation of treatment with corticosteroids, immunosuppressants, or tyrosine kinase inhibitors are of paramount importance. We present a case of ECD with multisystemic involvement, who was initially evaluated for the left lung mass and treated as tuberculosis, where fluorine-18-labeled fluorodeoxyglucose positron emission tomography/computed tomography aided in targeting the metabolically active site for biopsy as well as assessing the multisystemic involvement.