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Value of electron microscopy examination in the diagnosis of chronic alloimmune injury in renal allograf

Chronic alloimmune injury is a common cause of irreversible renal allograf failure. We evaluated the contribution of electron microscopy examination to the diagnosis of renal chronic rejection and the prognostic relevance of this diagnosis. From January 2011 to December 2012, we collected 21 consecutive samples of renal allograf biopsy specimens with a diagnosis of chronic rejection on electron microscopy examination. Submicroscopic findings were compared with those obtained by light microscopy to evaluate the additional information provided by electron microscopy. The outcome of the patients was assessed at 12 and 24 months postbiopsy. The submicroscopic data suggesting alloimmune injury were: (1) duplication of glomerular basement membranes in the absence of data of membranoproliferative glomerulonephris or thombotic microangiopathy and/or (2) multilayering of the basement membrane of the peritubular capillaries. Of the 21 samples of this series, the corresponding light microscopy also showed data of chronic allograft injury in 15 cases; the diagnosis of chronic rejection was based on electron microscopy exclusively in the remaining six cases (Figure 1). Twenty-four months after the diagnosis, 17 patients had returned to dialysis or were in predialytic state. Renal allograf survival has improved in the last decade, but, nowadays, the 10-year graft failure in adults receiving a kidney from deceased donors continues to be about 20% [1]. Long-term allograf malfunction is due to a large variety of, not mutually excluding, causes. The Banff classification emphasizes the importance of differentiating chronic rejection from other causes of transplant failure [2]. Two of the key data of chronic alloimmune injury, transplant glomerulopathy, and basal membrane reduplication of the intertubular capillaries may be subtle lesions and difficult to detect on light microscopy examination [3]. In our series, 6 of 21 cases with submicroscopic lesions attributable to alloimmune injury did not show findings of chronic rejection on light microscopy examination, even after careful review. Therefore, electron microscopy continues to be a valuable tool to detect incipient lesions in renal allograft. On the other hand, these lesions seem to be sign of poor outcome: 17 of our 21 patients had returned to dialysis or were in predialytic state 24 months after the detection chronic allograph injury.