Clinicopathologic Predictors of Reversibility Dialysis Dependent Acute Kidney Injury in Patients with Myeloma Cast Nephropathy
Authors: Kazarina Evgeniia V. , Rekhtina Irina G. , Stolyarevich Ekaterina S. , Kovrigina Alla M. , Dvirnyk Valentina N. , Kulikov Sergei M. , Mendeleeva Larisa , Savchenko Valeriy G. 
Published: November 2020

Abstract
Introduction: Myeloma cast nephropathy (MCN) is a main cause of acute kidney injury (AKI) at multiple myeloma (MM) onset. Wherein 5-9% of newly diagnosed MM patients are dialysis dependent. The introduction of novel agents has provided the achievement of rapid and deep hematologic response in most patients. However, the renal response in patients on dialysis is only 38-62.5%. The predictors of AKI reversibility in patients with MCN remain not enough studied.
Aim: to determine clinical, morphological and immunohistochemical predictors of reversibility dialysis dependent AKI in patients with MCN.
Materials and methods: 36 patients aged 38 to 74 years (median age=57 years) with newly diagnosed MM and dialysis dependent AKI stage 3 (AKIN, 2012) due to MCN were enrolled into the study from January 2006 till November 2019. The diagnosis of MM, hematologic and renal response were established according to the 2016 IMWG criteria. MCN was determined by renal biopsy performed prior to induction therapy.
The assessment degree of acute tubular injury, tubular atrophy and interstitial fibrosis (IF/TA) were semi-quantitatively evaluated. The number of sclerotic glomerular were calculated manually. The median number of casts was defined by all casts in a section divided by number of fields observed (х100). Additionally, square of interstitial fibrosis, interstitial inflammation, expression of Immunohistochemical markers (E-cadherin, α-smooth muscle actin (α-SMA), vimentin) were measured by computerized quantitatively image analysis using the digital module Leica (Germany). The time from diagnosis of AKI to start of induction therapy did not exceed 3 months. Bortezomib based first line treatment regimen was used in 25 (69%) of patients; 9 (25%) patients received chemotherapeutic agents only, 2 (6%) dead before a start of induction therapy. Statistical software package SAS 9.4 was applied for calculations. Overall survival according to renal response was compared by using Kaplan-Meier curves. Also frequency, logistic, discriminant and ROC analysis were used. All estimates are shown with a 95%CI.
Results: Hematologic partial response or better occurred in 19 (53%) of patients, median of 32 (13-129) days. Renal response - in 14 (39%). In 3 (8%) cases renal function improved after correction of dehydration before start of antimyeloma therapy, in the remaining 11 (30%) patients only when hematologic response was achieved (p = 0.001). The frequency of renal response was depending on start of antimyeloma therapy before and after 4 weeks from diagnosis of AKI and was 83% and 17%, respectively (p &lt;0.05). In patients with renal response there was not a single fatal outcome; without renal response 3-year OS was 68% ± 13%.
Patients with hematologic response were divided into two groups (Tab.). The main pathological findings associated with renal response were less frequent mild to severe IF/TA in patients with and without renal response (moderate 45% vs 75%, respectively, p=0.008), less area of interstitial fibrosis (24.9% vs 44.7%, respectively, p=0.001), percentage of proximal tubules with save epithelial phenotype and less area of expression E-cadherin at interstitium (15.9% vs 7.1%, respectively, p=0.006). The median number of casts per field was the same (6.4 and 6.3, p=0.64) as well as the percentage of tubule lumen obstruction by casts (13.6% and 15.1%, p=0.81). Statistically significant correlation between the expression area of E-cadherin and interstitial fibrosis was not found (Rs= -0.335, p= 0.065). Therefore, a combination of these factors can be used to predict renal response in the onset of AKI due to MCN (area under the ROC curve is 0.84). The prognostic model and logical rule allow to define groups of renal outcomes (Fig.). If expression area of E-cadherin is less than 10% and / or area of interstitial fibrosis is more than 40% of the interstitium, a renal response is unlikely (OR = 24.5) and will not be achieved in almost 90% of cases, despite hematological response.
Discussion.
Reversibility of dialysis dependent AKI due to MCN rely on the achievement of hematological response and the time from diagnosis of AKI to start of antimyeloma therapy. There are predictors of renal response of these patients determined by the severity of morphological changes: degree of IFTA, quantitative area of interstitial fibrosis and E-cadherin expression.

Disclosures
No relevant conflicts of interest to declare.