Combined crystal-storing histiocytosis, light chain proximal tubulopathy, and light chain crystalline podocytopathy in a patient with multiple myeloma: a case report and literature review.

BACKGROUND: Crystal-storing histiocytosis (CSH), light chain proximal tubulopathy (LCPT), and light chain crystalline podocytopathy (LCCP) are rare complications of multiple myeloma (MM) or monoclonal gammopathy of renal significance, and their diagnoses are challenging. CASE PRESENTATION: In this case, a 69-year-old Chinese woman presented with suspicious Fanconi syndrome with renal insufficiency. Immunofixation electrophoresis of both serum and urine revealed elevated immunoglobulin G kappa (IgGkappa) and kappa light chain. Bone marrow aspirate revealed 15% plasma cells with considerable cytoplasmic granular inclusions and needle-shaped crystals. Renal biopsy confirmed the final pathologic diagnosis of kappa-restricted CSH, combined LCPT and LCCP by immunoelectron microscopy. A number of special casts were present which could easily be misdiagnosed as light chain cast nephropathy. Immunofluorescence on frozen tissue presented false negative for kappa light chain, as ultimately proven by paraffin-embedded tissue after pronase digestion. MM and CSH were diagnosed, and two cycles of chemotherapy were given. The patient subsequently refused further chemotherapy, and her renal function remained relatively stable during a 2.5-year follow-up period. CONCLUSIONS: In conclusion, we report a rare case of generalized kappa-restricted CSH involving bone marrow and kidney, combined with LCPT and LCCP, provide a comprehensive summary of renal CSH, and propose a new nomenclature of monoclonal immunoglobulin-induced crystalline nephrology. The presentation of monoclonal immunoglobulin and Fanconi syndrome should suggest the presence of monoclonal immunoglobulin-induced crystalline nephrology. Use of paraffin-embedded tissue after pronase digestion and immunoelectron microscopy is beneficial to improve the sensitivity of diagnosis.

Clinicopathological manifestations of coexistent monoclonal immunoglobulin deposition disease and immunotactoid glomerulopathy.

Combination of monoclonal immunoglobulin deposition disease (MIDD) and immunotactoid glomerulopathy (ITG) is a rare form of monoclonal immunoglobulin (MIg)-associated renal disease. We retrospectively reviewed the native kidney biopsy specimens at Peking University People's Hospital from 2011 to 2020. Five patients were diagnosed as MIDD + ITG. Their clinical and pathological characteristics were studied. The typical clinical features were nephritic syndrome and renal dysfunction with prominent anemia, but hematuria was mild. Unlike single MIDD and single ITG, on light microscopy, segmentally distributed mesangial nodular sclerosis on the basis of mesangial matrix hyperplasia was the major lesion. Others including membranoproliferative glomerulonephritis (MPGN)-like lesion, glomerular basement membrane thickness, and mild to moderate mesangial and endothelial proliferations might presented at the same time and in the same glomeruli. On immunofluorescence, MIg, usually monoclonal light chains, deposited along glomerular basement membranes and tubular basement membranes, while the intact MIg or monoclonal heavy chain deposited in the mesangial regions. Corresponding to the depositions on immunofluorescence, punctate "powdery" deposits along glomerular basement membranes and tubular basement membranes under electronic microscopy indicated the presence of MIDD. Microtubular substructures (diameters of 20-50 nm) exhibiting hollow cores arranged in parallel arrays in mesangial regions indicated the presence of ITG. Patients treated with bortezomib-based regimen seemed to have better outcomes. In conclusion, MIDD + ITG is a rare combination form of MIg-associated renal disease. Accurate diagnosis requires the comprehensive pathological investigations.

Coexistence of Light- and Heavy-Chain Deposition Disease and Immunotactoid Glomerulopathy in a Patient with Multiple Myeloma: A Case Report.

Multiple myeloma is a malignant neoplasm leading to a variety of renal diseases. Although most patients have only one pattern of renal pathology, two or more patterns can exist in some patients. Here, we report a 61-year-old man with multiple myeloma developed proteinuria, hematuria, hypertension, and renal insufficiency. A combined presentation of light- and heavy-chain deposition disease and immunotactoid glomerulopathy was proved by kidney biopsy. Treatment of multiple myeloma resulted in a complete resolution of the renal manifestations. This case illustrates the complexity of paraprotein associated renal lesions and emphasizes that further studies examining the physiologic properties and pathologic effects of monoclonal immunoglobulin are needed.

Renal outcomes of idiopathic and atypical membranous nephropathy in adult Chinese patients: a single center retrospective cohort study.

BACKGROUND: Membranous nephropathy (MN) is mainly classified into idiopathic MN (iMN) and secondary MN in etiology. In recent years, a new kind of membranous nephropathy, atypical membranous nephropathy (aMN) which shows "full house" in immunofluorescence but without definite etiology was paid more attention. In a single center cohort, the renal outcomes of iMN and aMN were compared. METHODS: iMN and aMN patients were selected from renal pathology databank from January 2006 to December 2015. Patients' demographics, laboratory values, induction regimens and patients' responses were recorded. Specially, creatinine, eGFR, albumin and 24 h urinary protein excretion were recorded at 6th month after the induction of immunosuppressive (IS) treatment and at the end of follow up. Complete proteinuria remission was defined as urinary protein < 0.3 g/d, partial proteinuria remission was defined as urinary protein between 0.3 g/d ~ 3.5 g/d and decreased > 50 % from the baseline. The primary outcome was worsening renal function, defined as a 30 % or more decrease in eGFR or end-stage renal disease (eGFR < 15ml/min/1.73m2). COX proportional hazard models were used to test if aMN was a risk factor of worsening renal function compared with iMN. RESULTS: There were 298 patients diagnosed with MN and followed in our center for 1 year or more, including 145 iMN patients with an average follow-up time of 4.5 ± 2.6 years, and 153 aMN patients with 4.1 ± 2.0 years (p = 0.109). The average age of iMN patients was older than aMN patients (56.1 ± 12.2 versus 47.2 ± 16.2 years old, p < 0.001). There were 99 iMN patients and 105 aMN patients with nephrotic range proteinuria and without previous immunosuppressive treatment. 93 (93.9 %) and 95 (90.5 %) patients underwent immunosuppressive treatment in iMN and aMN group, and there was no significant difference of the overall proteinuria remission rates at 6th month (59.1 % vs. 52.0 %, p = 0.334) and endpoint (73.7 % vs. 69.5 %, p = 0.505) between the two groups. 25 (25.3 %) patients in iMN group and 21 (20.0 %) patients in aMN group reached primary endpoint (X2 = 0.056, p = 0.812). Multivariate COX regression showed that after demographics, baseline laboratory values and remission status at 6th month were adjusted, aMN group had similar renal outcome compared with iMN group, the HR of primary outcome was 0.735 (95 % CI 0.360 ~ 1.503, p = 0.399). CONCLUSIONS: The proteinuria remission rates and renal outcomes were similar in iMN and aMN patients after covariables were adjusted.