The Matter of Kidney Biopsy in Monoclonal Gammopathy of Renal Significance: A Case Report of a New Pattern of Immunoglobulin-Storing Histiocytosis.

Monoclonal gammopathy of renal significance (MGRS) represents a group of disorders, characterized by paraproteinemia which causes renal damage. These disorders never meet the diagnostic criteria for multiple myeloma (MM) or lymphoproliferative disease. Crystal-storing histiocytosis is one of the rarest patterns of MGRS, characterized by an accumulation of light chains of crystals within histiocyte's cytoplasm, located in bone marrow or other extramedullary sites such as the kidney, cornea, or thyme. A very few cases have been described as immunoglobulin-storing histiocytosis (IgSH) without evidence of crystals. In the recent literature, only 3 cases of IgSH have been described so far, none renal. In all cases, these very peculiar histopathological patterns are associated with lymphoproliferative or plasma cellular disorders. Here, we report a very unusual IgSH pattern in a kidney biopsy, which led to prompt detection and early therapeutic intervention, in a patient with otherwise misdiagnosed MGRS.

Clinical outcomes and temporal trends of immunological and non-immunological rare diseases in adult kidney transplant.

BACKGROUND: Rare diseases (RDs) encompass many difficult-to-treat conditions with different characteristics often associated with end-stage renal disease (ESRD). However, data about transplant outcomes in adult patients are still lacking and limited to case reports/case series without differentiation between immunological/non-immunological RDs. METHODS: Retrospective analysis among all adult kidney transplanted patients (KTs) with RDs (RDsKT group) performed in our high-volume transplantation center between 2005 and 2016. RDs were classified according to the Orphanet code system differentiating between immunological and non-immunological diseases, also comparing clinical outcomes and temporal trends to a control population without RDs (nRDsKT). RESULTS: Among 1381 KTs, 350 patients (25.3%) were affected by RDs (RDsKTs). During a f/up > 5 years [median 7.9 years (4.8-11.1)], kidney function and graft/patient survival did not differ from nRDsKTs. Considering all post-transplant complications, RDsKTs (including, by definition, patients with primary glomerulopathy except on IgA nephropathy) have more recurrent and de-novo glomerulonephritis (14.6% vs. 9.6% in nRDsKTs; p = 0.05), similar rates of de-novo cancers, post-transplant diabetes, dysmetabolism, hematologic disorders, urologic/vascular problems, and lower infectious episodes than nRDsKTs (63.7% vs 72.7%; p = 0.013). Additional stratification for immunological and non-immunological RDsKTs or transplantation periods (before/after 2010) showed no differences or temporal trends between groups. CONCLUSIONS: Kidney transplant centers are deeply involved in RDs management. Despite their high-complex profile, both immunological and non-immunological RDsKTs experienced favorable patients' and graft survival.

Detection of urinary podocytes by flow cytometry in idiopathic membranous nephropathy.

Idiopathic membranous nephropathy (iMN) is considered an immune-mediated disease where circulating autoantibodies against podocyte targets (mainly the PLA2R) cause the deposition of in-situ subepithelial immune-complexes. The consequent podocyte damage may cause cell detachment in urine (Podocyturia-PdoU). PdoU has been assessed in different kidney diseases, but limited data are available in iMN. In this study all patients with a diagnosis of iMN between 15/12/1999-16/07/2014 were tested for PLA2R antibodies (Ab anti-PLA2R, ELISA kit) and PdoU by flow cytometry with anti-podocalyxin antibody. A semi-quantitative PdoU score was defined according to the percentage of podocalyxin positive cells normalized to the total volume of sample and set relative to the urine creatinine measured in the supernatant. PdoU was positive in 17/27 patients (63%; 1+ score in 6/27-22.2%, 2+ in 4/27-14.8%, 3+ in 2/27-7.4%, 4+ in 5/27-18.5%). Only 2/7 patients with complete remission showed a positive PdoU (1+) while all six patients without remission have significant PdoU. PdoU+ was statistically correlated with the absence of remission and Ab anti-PLA2R + (p < 0.05) but PdoU, analysed as a continuous variable, showed a non-linear correlation with proteinuria or PLA2R antibody levels also in the cohort of patients with two available PdoU tests. In conclusion, PdoU could be detected in iMN and seems to be associated with commonly considered markers of disease activity (proteinuria and Ab anti-PLA2R) with a non-linear correlation. Despite data should be confirmed in large and prospective cohorts, according to the podocyte depletion hypothesis PdoU may represent an early marker of immunological activation with potential prognostic utility.