Proliferative Glomerulonephritis With Monotypic Immunoglobulin Deposits of IgG1 Subclass: A Case Series
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Published on: June 8, 2022
Lihong Bu1, Lisa E Vaughan2, Samar M Said3
1Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN.
Rationale & Objective:
Most cases of proliferative glomerulonephritis with monotypic immunoglobulin deposits (PGNMID) are associated with IgG3. The characteristics of IgG1 deposits within PGNMID have not been well defined and are the focus of this study.
Study Design:
Retrospective case series.
Setting & Participants:
Forty-six PGNMID cases with granular monotypic IgG1 deposits (PGNMID-IgG1) identified in nephropathology archives.
Findings:
57% of cases were male and 78% had hematuria. The median age was 57 years, the median proteinuria level was 4.8 g/day, and the median eGFR level was 52 mL/min/1.73 m2. Hypocomplementemia was uncommon (12%). Kidney biopsy revealed MPGN (54%) or mesangial proliferative GN (33%), with membranous features in nearly half (43%). A nephropathic clone or monoclonal Ig (mIg) was detected in 19 of 42 patients with PGNMID-IgG1 who underwent evaluation, including 10 with chronic lymphocytic leukemia or small lymphocytic lymphoma (CLL/SLL). Among patients >50 years, the detection rate was 72% (18/25) vs. 6% (1/17) among younger patients. SPEP/SIF detected the nephropathic mIg in 13 of 40, and bone marrow biopsy done in 25 detected clonal B-cells in eight and clonal plasma cells in two patients. Follow-up (median 27 months) was available for 37 patients. Ten (83%) of 12 patients with an identifiable clone or mIg responded to clone-targeted (anti-plasma or B- cell) therapy, whereas 4 of 8 patients without an identifiable clone or mIg responded to anti-plasma cell therapy. At 60 months, the overall cumulative incidence of kidney failure requiring dialysis or death was 31.1% (7.9% to 48.5%). Four patients underwent kidney transplantation and three with transplant biopsies exhibited recurrent disease.
Limitations:
Retrospective, single-center study, non-standardized hematologic workup and management.
Conclusions:
Nearly 75% of PGNMID-IgG1 cases >50 years of age have a clonal population detected and nearly a quarter have CLL/SLL. Response to anti-B-cell therapy may be greater in those with an identifiable clone or mIg. These data may inform treatment strategies for people with PGNMID-IgG1.
