#6026 EVOLUTION OF MONOCLONAL GAMMOPATHY OF UNCERTAIN SIGNIFICANCE IN KIDNEY TRANSPLANT RECIPIENTS
Authors: González-García Celia , Berzal Raquel , Hernández Paúl , Martínez Marta Rivero , García-Galán Lucía Cordero , González Aida Frías , García Julio Francisco Colina , Lozano Sergio Huerga , Sevillano Angel , Pérez Justo César Sandino , Morales Enrique 
Published: June 2023

Abstract

Background and Aims
Monoclonal gammopathy of uncertain significance (MGUS) is a frequent condition with an estimated prevalence of 3% in people over 50 years of age in the general population. Nowadays, more kidney transplants (KT) are performed in a population susceptible to present MGUS, and the evolution of this entity in KT recipients is currently unknown.

Method
We carried out a retrospective study of a cohort of KT recipients diagnosed with MGUS between 1996 and 2020, including patients with MGUS identified prior to kidney transplantation or during follow-up. We describe baseline, kidney transplantation, and hematological characteristics, analyzing the evolution of the hematological parameters according to the moment of appearance of MGUS.

Results
A total of 51 patients were included; in 28 (54.9%) MGUS appeared before transplantation, and in 23 (45.1%) after transplantation. Thirty-two (62.7%) were males, with glomerular pathology in 17 (33.3%) as the leading cause of chronic kidney disease. Hypertension (90.2%) and diabetes (27.5%) were the most common comorbidities. At renal transplantation, the median age is significantly higher in the pre-transplant MGUS group (62 years [IQR 54-66]) vs. 48 years [IQR 40-68]; p = 0.04). This group had a higher induction immunosuppression load than the post-transplant MGUS group (p = 0.01) due to a greater incidence of immunized KT recipients (p = 0.05). There were no differences in rejection, infections, or post-transplant neoplasia between both groups; however, higher renal graft loss was observed in the post-transplant MGUS group (10.7% vs. 43.5%; p = 0.02), probably explained by a longer follow-up time in this group. The most detected paraprotein was IgG (60.8%) and lambda light chain (51%), with a median blood concentration of 0.4 g/dl (IQR 0.2-1.4). In 45.1% of the cases, the paraprotein remained stable; it disappeared in 27.5%, and MGUS progressed to hematological neoplasia in 21.6%, including multiple myeloma, amyloidosis, and post-transplant proliferative syndrome. We did not detect significant differences in the evolution according to the moment of diagnosis of the MGUS (p = 0.7). Twelve renal biopsies were performed during post-transplant follow-up, detecting renal involvement by paraprotein in 5 (9.8%). Only 1 of them (1.96%) was defined as a monoclonal gammopathy of renal significance for not meeting the criteria for malignancy.

Conclusion
Close monitoring of MGUS in KT recipients is still necessary given the possibility of progression to hematological neoplasia, with a non-negligible percentage in our serie of patients. Our cohort does not allow us to detect significant differences with an impact on the clinical course of MGUS or KT regarding the moment of the development of MGUS before or after transplantation.