18F-FDG PET/CT as non-inasive tool to assess transplanted pancreas graft rejection

Aim: Currently, there are no available tool able to non-invasively define the presence of transplanted pancreas graft rejection; therefore, graft biopsy is nowadays the only available diagnostic tool for pancreas graft rejection. The aim of the present study is to assess the role of 18F-FDG PET-CT in detecting and monitoring pancreas graft rejection. Materials and Methods: Retrospective study including 12 patients (6M and 6F; mean age at transplant: 45±12 yrs; mean duration of diabetes 24±11yrs) who underwent pancreas transplantation alone (PTA) or simultaneous pancreas-kidney transplant (SPK) in the past. Mean duration of diabetes was 24±11 yrs. 18F-FDG PET/CT was performed in all patients according to the following clinical indications: i) suspicion of pancreas graft rejection (n=9) based on hyperglycemia, abdominal pain and/or high serum amilase/lipase; ii) suspected lymphoproliferative disease (n=1); iii) oncological follow-up (1 melanoma and 1 solitary lung nodule). The cohort included patients suspected for acute pancreas graft rejection (REJ, based on graft biopsy and/or presence of donor-specific antibodies; n=9) and control patients with no rejection. A subgroup of patients (n=4) underwent to a further follow-up 18F-FDG PET/CT after treatment of graft rejection. PET/CT images were interpreted qualitatively (focal, diffuse homogenous, diffuse non-homogeneous; Visual scale: 0= no uptake or less than the liver; 1=liver uptake; 2>liver uptake) and semi quantitatively with the assessment of the following parameters: maximum and mean standardized Uptake Value (SUVmax and SUV mean, respectively).

Results: Six patients have been diagnosed with acute graft rejection. In the CTR group, final diagnoses included normal findings (2), post-transplant lymphoproliferative disease (1), chronic reactive lymphadenitis (1), pneumonia (1), enteritis (1). Visual scale showed a score of 2 in 7 patients (6 diffuse non-homogeneous and 1 diffuse homogenous) and a score of 0 in the remaining 5 patients (qualitative tracer distribution not applicable). The diffuse, non-homogenous pattern tended to be more frequent in REJ vs. CTR. Significantly higher SUVmax and SUVmean were observed in REJ vs. CTR (p=0.036 and p=0.029, respectively). When the analysis was restricted to REJ and CTR patients who underwent 18F-FDG PET/CT for clinical suspicion of rejection, statistical significance was lost. A significant decrease both in SUVmax and SUVmean (p<0.05 for both comparisons) was observed in the follow-up scans after treatment for graft rejection, which was consistent with the clinical response to treatment.

Conclusions: Diagnoses of acute pancreas rejection can be suspected based on 18F-FDG PET/CT SUVmax and SUVmean, although further investigation is advocate because of the small sample size of the present study. Considering the significant decrease in SUV after treatment for rejection, a possible role of 18F-FDG PET/CT as a tool for monitoring response to treatment could be suggested.