False positive PET-CT result after treatment of a patient with diffuse large B-cell lymphoma Clinical case

The use of 18F-fluorodeoxyglucose positron emission tomography (PET-СT) to determine the initial stage and assess response to treatment in aggressive lymphomas is considered the standard. Evaluation of bone marrow infiltration in PET-CT with 18F-fluorodeoxyglucose usually allows to distinguish normal regenerating bone marrow after chemotherapy by its characteristic absorption. A 54-year-old patient was diagnosed with diffuse large B-cell lymphoma with focal lesions in the lymph nodes and bone marrow with osteodestruction of the lytic type. Therapy at the A.F. Tsyb Medical Radiological Research Center consisted of 6 cycles of R-EPOCH with intrathecal administration of drugs for the prevention of neuroleukemia (dexamethasone + cytarabine + methotrexate), completed in December 2022. On intermediate PET-CT after 2 cycles, the glycolysis intensity was completely normalized. During the observation in February 2023, PET-CT showed an increase in the level of metabolism in one of the foci of osteodestruction in the pelvic bones. A guided biopsy of the lesion in March 2023 was performed, morphological conclusion: absence of signs of diffuse large B-cell lymphoma, elements of hematopoiesis of the bone marrow. In June 2023, repeated PET-CT showed continuing increase in contrast accumulation in the previously identified foci. Trephine biopsy in July 2023 showed a picture of hematopoietic foci in the bone marrow, a sign of remission. PET-CT scan in December 2023 showed a decrease in the intensity of glycolysis in the foci in the pelvic bones confirming remission of the disease. In the era of rituximab, false-positive PET-CT results are detected with greater frequency, therefore, their assessment and correct interpretation, as well as additional clarification using other available techniques, are necessary in modern clinical practice to choose tactics for further therapy.