Angioi, Andrea

ABSTRACT Background Diagnostic interpretation of kidney allograft biopsies using the Banff classification remains variable, but the determinants of this variability are not fully defined. We performed a global, fully digital multi-reader study to identify the principal drivers of disagreement in Banff-based assessment. Methods Thirty-six kidney transplant biopsies were independently scored by 67 renal pathologists on a standardized digital platform. Readers assessed Banff lesions on hematoxylin and eosin, periodic acid–Schiff, and Jones’ silver stains; final diagnostic categories were assigned using prespecified Banff-based decision rules. Interobserver agreement was quantified with Gwet’s agreement coefficient (AC) statistics. Determinants of diagnostic agreement were evaluated using pairwise mixed-effects logistic regression, and reader similarity was examined by principal component analysis (PCA) with post hoc molecular annotation. Results Agreement for final diagnostic categories was moderate (Gwet’s AC1, 0.55; 95% CI, 0.47–0.63). Lesion-level agreement varied substantially, with lowest agreement for selected threshold-dependent inflammatory or semi-quantitative lesions, including interstitial inflammation in areas of IFTA, peritubular capillaritis and arteriolar hyalinosis. Diagnostic concordance differed markedly across biopsies, indicating strong case-level heterogeneity. In pairwise models, differences in active inflammatory and vascular lesion scoring were the strongest correlates of diagnostic disagreement; reader experience and geography contributed minimally. Principal component analysis showed reader variation was organized along two dominant axes: a rejection-calling threshold axis linked mainly to tubulointerstitial inflammatory injury, and a T cell-mediated (TCMR/TI) and antibody-mediated/microvascular (AMR/MVI) inflammation-oriented phenotypic classification axis. Conclusion Interobserver variation in Banff-based kidney transplant biopsy assessment is structured rather than random and driven mainly by how readers threshold and integrate key inflammatory lesion compartments rather than experience or geographic location.

ABSTRACT Background Membranous nephropathy (MN) is a leading cause of nephrotic syndrome (NS). Since the identification of anti–phospholipase A2 receptor (anti-PLA2R) antibodies in 2009, the use of laser microdissection and tandem mass spectrometry (LMD/MS) has allowed the discovery of several target antigens in MN. Methods In this retrospective cohort study, adult patients evaluated at the Division of Nephrology at Brotzu Hospital (Cagliari, Italy) with biopsy-proven MN and a negative serological test for anti-PLA2R antibody underwent LMD/MS, performed at the Department of Laboratory Medicine and Pathology of Mayo Clinic (Rochester, MN, USA). Results Twenty-four cases of biopsy-proven MN were available for antigen detection by LMD/MS studies. High total spectral counts of PLA2R were detected in 12 out of 24 (50%) cases. In addition, high spectral counts of THSD7A and NELL1 were detected in two cases each, and EXT1/EXT2 and NCAM1 in one case each. Five putative antigens have been detected: SULF1, PGLYRP, HYAL1, THBS and SEZ6L2. Conclusions Our study highlights at least two interesting considerations. First, the determination of PLA2R on renal tissue in the diagnosis of PLA2R-associated MN is emphasized since 50% of our cases were falsely diagnosed with PLA2R-negative MN based on the serum anti-PLA2R antibodies determination. Second, our study shows six patients with MN likely associated with putative antigens, two of them showing new antigens never described before in literature (HYAL1 and THBS1). This high prevalence of putative antigens in our cohort is not easily explainable and paves the way for evaluating specific factors in the Sardinian population that could explain this evidence.

Abstract Interstitial nephritis associated with multiple myeloma (LCTIN) is a rare histological finding defined as an abundant inflammatory infiltrate of polyclonal lymphocytes and plasma cells in the interstitium, not related to secondary causes other than a coexistent malignant plasma cell dyscrasia. The present case report illustrates an LCTIN associated with a light chain proximal tubulopathy, secondary to a kappa light chain MM, previously addressed as steroid-resistant drug-induced interstitial nephritis.

Abstract Light chain cast nephropathy (LCCN) in multiple myeloma often leads to severe and poorly reversible acute kidney injury. Severe renal impairment influences the allocation of chemotherapy and its tolerability; it also affects patient survival. Whether renal biopsy findings add to the clinical assessment in predicting renal and patient outcomes in LCCN is uncertain. We retrospectively reviewed clinical presentation, chemotherapy regimens, hematologic response, and renal and patient outcomes in 178 patients with biopsy-proven LCCN from 10 centers in Europe and North America. A detailed pathology review, including assessment of the extent of cast formation, was performed to study correlations with initial presentation and outcomes. Patients presented with a mean estimated glomerular filtration rate (eGFR) of 13 ± 11 mL/min/1.73 m2, and 82% had stage 3 acute kidney injury. The mean number of casts was 3.2/mm2 in the cortex. Tubulointerstitial lesions were frequent: acute tubular injury (94%), tubulitis (82%), tubular rupture (62%), giant cell reaction (60%), and cortical and medullary inflammation (95% and 75%, respectively). Medullary inflammation, giant cell reaction, and the extent of cast formation correlated with eGFR value at LCCN diagnosis. During a median follow-up of 22 months, mean eGFR increased to 43 ± 30 mL/min/1.73 m2. Age, β2-microglobulin, best hematologic response, number of cortical casts per square millimeter, and degree of interstitial fibrosis/tubular atrophy (IFTA) were independently associated with a higher eGFR during follow-up. This eGFR value correlated with overall survival, independently of the hematologic response. This study shows that extent of cast formation and IFTA in LCCN predicts the quality of renal response, which, in turn, is associated with overall survival.