The Sensitivity and Specificity of 18F-Fluorodeoxyglucose Positron Emission Tomography -Computed Tomography for the Diagnosis and Monitoring of Acute Graft vs. Host Disease

Graft versus host disease (GVHD) is one of the major causes of death in patients undergoing allogeneic hematopoietic cell transplantation (HCT). Despite prophylactic measures, the incidence of acute GVHD is estimated at 40-60% among patients receiving allograft from HLA-identical sibling donors, and may even reach 75% in patients receiving HLA-matched unrelated grafts. Approximately 20% of the patients will develop the severe variant of the disease and there is a tight association between the severity of GVHD and transplantation-related-mortality. The treatment of GVHD is largely based on high dose steroids regimen which is associated with long term morbidity and mortality. In the subgroup of patients with steroid-refractory or slowly resolving GVHD, there are currently no recommendations on the best timing of tapering down the steroids dose in the case of resolution of the disease, or adding a second line medication, in case of non-resolving or progression of the symptoms.

18F-FDG PET/CT (2-[fluorine-18] fluoro-2-deoxy-D-glucose, Positron emission tomography- CT) is a noninvasive technique that allows quantifying and precisely localizing 18F-FDG uptake in the entire body. 18F-FDG uptake is caused by increased local metabolic activity. Such increased uptake has been described not only in neoplastic lesions but also in inflammatory lesions (2). In this condition, uptake has been correlated with local stimulation of tumor necrosis factor, and with monocyte priming and activation. A physiologic variable uptake may be observed in the bowel, especially the cecum, and has limited the use of PET in inflammatory bowel diseases. The advantage of combined PET and CT devices leads to significant improvements in the interpretation of the bowel areas, and greatly reduces the number of false-positive findings in the gastrointestinal tract.

CT-PET has been recently evaluated in our center as a diagnostic tool for Crohn disease. In this study, CT-PET had a good correlation between FDG uptake and the severity of Crohn disease. In the acute GVHD setting, a study reported on a small cohort suggested a correlation between CT-PET findings, FDG uptake, and the diagnosis of lower gut acute GVHD.

In this study, we aim to evaluate and characterize the correlation between CT-PET findings in patients suspected to have acute GVHD, and the disease course.