LAUSR

Kidney transplantation is the best treatment option for patients with end-stage renal disease. Despite major improvements in surgical techniques and immunosuppression therapy, today, long-term allograft survival after kidney transplantation remains a major clinical issue. The most common cause of late allograft failure is chronic allograft nephropathy (CAN), which is a consequence of various immune-dependent and immune-independent factors. Aside from other histological findings (glomerulopathy, tubular atrophy, vasculopathy), the most prominent histological characteristic of CAN is interstitial fibrosis, which is a strong predictor of kidney allograft failure, and the early appearance of CAN is an independent predictor for poor long-term kidney transplant survival. Biopsy remains the “gold standard” for the evaluation of kidney allograft dysfunction, thus some transplant units carry out protocol biopsies for CAN detection. However, kidney biopsy has some limitations, such as its invasive nature (with risk of complications) and sampling error, as well as total costs and patient discomfort. In contrast, some transplant centers monitor changes in serum creatinine values in order to detect CAN, but this occurs late in the course of the disease when significant and irreversible histological changes have already developed, precluding timely interventions in order to prevent further damage to the kidney transplant. Therefore, non-invasive methods for early CAN detection are required. Ultrasound elastography (UE) methods determine tissue stiffness, and have been extensively evaluated in the context of liver fibrosis in the past two decades. In recent years, some investigators reported on the efficacy of UE methods in evaluating kidney allograft fibrosis. A few years ago, we published our results on the usefulness of transient elastography in the assessment of CAN in our renal transplant recipients. However, transient elastography allows only unidimensional measurements without the possibility to precisely position and to adjust the size and depth of the region of interest for stiffness evaluation. Thus, we rejoice in reading the great experience of Ma et al. from Hong Kong that evaluated the use of shear wave elastography (SWE) in the assessment of kidney allograft tubulointerstitial fibrosis, which is a real-time two-dimensional method that allows clinicians to precisely choose the region of interest for stiffness evaluation. The authors investigated the relationship between tissue stiffness and histological severity of tubulointerstitial fibrosis in 32 patients. Interestingly, they showed that the tissue stiffness determined by SWE correlated with the histological severity of interstitial fibrosis and tubular atrophy, with good interobserver agreement. More importantly, SWE performed better than serum creatinine in detecting early tubulointerstitial fibrosis. To conclude, we agree with the authors that SWE and other two-dimensional UE methods have the potential to become non-invasive bedside tests for screening patients at risk for early changes related to CAN. These methods are promising because they are reliable, noninvasive, safe, fast, low cost, increasingly available and can be carried out on an ambulatory basis. However, these methods cannot verify the cause of CAN and the degree of fibrosis, thus, the current value of UE methods in the assessment of kidney allograft function still remains experimental and more in the field of screening or follow-up methods. More investigations with larger sample sizes are required to define the exact role of these methods in kidney transplantation patients. As other authors also suggested, the main role of UE methods could be in the long-term observation and evaluation of allograft fibrosis during follow up, possibly selecting patients for timely (re)evaluation with kidney biopsy.