Role of 18F-FDG PET/CT imaging for evaluation of diagnosed or clinically suspected post-transplant lymphoproliferative disorders: a tertiary care center experience.

Objectives: Post-transplant lymphoproliferative disorder (PTLD) is a well-known grave complication of both solid organ and hematopoietic stem cell transplantation. Early diagnosis of this complication is of utmost significance and depends on a combination of clinical, imaging and histological findings. While F-18 FDG PET/CT has become an established imaging modality in the management of FDG-avid lymphomas, its role in PTLD needs further evaluation. The present study was intended to evaluate the role of F-18 FDG PET/CT in patients with diagnosed or suspected PTLD.

Methods: This is a retrospective, single center, observational study. Records of consecutive patients who had undergone F-18 FDG PET/CT for initial staging of pathologically proven or clinically suspected PTLD from January 2010 to December 2019 were reviewed. Two experienced nuclear Medicine physicians reviewed the FDG PET/CT images for visual and semi quantitative measurement and any disagreement was resolved with mutual consensus. The results of F-18 FDG PET/CT scans were compared with prior performed conventional imaging (CT scan) modalities and histological findings.

Results: A total of 33 patients (23 males and 10 females, median age: 34 years, range: 3-61 years) who had undergone F-18 FDG PET/CT were reviewed. Twenty-nine participants had prior renal transplant while the remaining four had hematopoietic stem cell transplantation. Of these 21/33 patients had histo-pathologically proven PTLD and underwent FDG PET/CT scan for initial staging while remaining 12/33 patients were subjected to the PET/CT scans due to high clinical suspicion of disease. In the biopsy-proven PTLD group, positive F-18 FDG PET/CT results were obtained in all the patients [median lesion SUVmax 13.1, interquartile range (IQR): 7.9-17.6]. On per-lesion analysis, F-18 FDG PET/CT showed more lesions than the conventional imaging modalities (71 versus 27), but CT revealed 2 lesions which were negative on F-18 FDG PET/CT. On per-patient analysis, F-18 FDG PET/CT identified more occult lesions in 17/21(81%) patients and resulted in the upstaging of 3/21(14%) patients while comparing with conventional imaging. Among the 12 patients with clinically suspicious PTLD, F-18 FDG PET/CT was positive in six patients (median lesion SUVmax 6.3, IQR: 2.9-11.8). Of these five were diagnosed as PTLD and one as tuberculosis.

Conclusions: F-18 FDG PET/CT imaging is very beneficial in evaluation of PTLD, particularly in the detection of occult lesions missed on conventional imaging modalities and helped in upstaging the disease in a significant number of patients. Additionally F-18 FDG PET/CT imaging is also helpful in evaluation of clinically suspicious PTLD and can further assist in guiding biopsies for accurate histo-pathological diagnosis.