Could Rebound Thymic Hyperplasia Be the First Sign of Rejection in Renal Transplant Recipients?

Abstract Background/Aim To determine the prevalence of rebound thymic hyperplasia in the follow-up of renal transplant recipients in our hospital and evaluate the relationship between thymic hyperplasia and histopathologically confirmed allograft rejection. Materials and Methods Our study retrospectively examined the postoperative computed tomography images of 341 kidney transplant recipients between 2012 and 2023, and 229 patients were included in the study. Thymic hyperplasia was defined as an increase in size and volume exceeding 30%. The relationship between thymic hyperplasia and the results of the true-cut biopsy of the graft kidney was evaluated in these patients. Results Thymic hyperplasia was detected in 10 (4.4%) patients, of whom seven (70%) had biopsy-proven acute rejection, including four cases of acute humoral rejection and three cases of T-cell-mediated acute rejection (two of type 2a and one of type 1a). Among the 219 patients without detected thymic hyperplasia, 89 (40.6%) exhibited rejection, 72 (80.9%) of which were acute rejections, while 17 (19.1%) were chronic rejections. No statistically significant difference was observed in rejection rates between the groups with and without thymic hyperplasia ( p = 0.066). However, this result can be attributed to the small number of patients in the thymic hyperplasia group. Conclusion In our study, patients with thymic hyperplasia exhibited higher rates of acute rejection than those without thymic hyperplasia, although no chronic rejection was observed in this group. We suggest that thymic hyperplasia might be associated with acute rejection. Multicenter, randomized controlled studies with larger patient groups are needed to strengthen this study further.