False positive spinal cord uptake on fluorodeoxyglucose positron‐emission tomography following treatment of lymphoma

Abstract

A 19-year-old woman with no previous medical history was diagnosed with a stage IV primary mediastinal large B-cell lymphoma with a bulky mass and an International Prognostic Index score of 3 (left). After 6 cycles of R-CHOP14 (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisolone at 14 d intervals) a combined F-fluorodeoxyglucose positron-emission tomography (F-FDG-PET) and computed tomography (CT) scan was performed (Siemens biograph mCT with 64 slices, 135 MBq F-FDG with at least 6 h fasting prior to intravenous injection). The scan showed a partial remission with persisting F-FDG PET-positive mediastinal lymphadenopathy. She received 30 Gy radiation and a boost up to 40 Gy to the F-FDG PET-positive lesions. Response evaluation after treatment showed intense F-FDG uptake in the spinal cord at the level of the eleventh and twelfth thoracic vertebrae (right). She had no neurological symptoms. The role of F-FDG PET in staging and evaluation of remission in lymphomas is well established. The incidence of central nervous system (CNS) recurrence is reported to be 2–5%. In this case, the end-of-treatment F-FDG PET showed abnormal spinal F-FDG uptake and CNS progression of the lymphoma was considered. Magnetic resonance imaging of the spinal cord showed no lesions. The F-FDG uptake in the spinal cord was therefore considered to be false positive. It appears that this physiological phenomenon is encountered in up to half of cancer patients and is seen more often in winter (Amin, A., Rosenbaum, S.J. & Bockisch, A. (2012) Physiological F FDG uptake by the spinal cord: is it a point of consideration for cancer patients? Journal of Neurooncology, 107, 609–615). Increased F-FDG uptake is primarily seen at the level of the cervical vertebrae, the eleventh and twelfth dorsal vertebrae, and the first lumbar vertebrae. The CNS is highly dependent on glucose and accounts for 50% of glucose metabolism. During fasting and stress conditions, such as during the F-FDG PET-CT procedure, there is a physiological increase in glucose uptake in the CNS to maintain a steady glucose state. This mechanism probably accounts for the increased F-FDG uptake observed in the spinal cord of our patient. This case illustrates the potential pitfalls of normal physiological F-FDG uptake in the spinal cord, which is frequently encountered in cancer patients. Awareness of this pitfall can avoid additional diagnostic procedures.