Clinical Case and Discussion 90

Which has a better prognosis?

C3GN, idiopathic	1 (16%)
C3GN secondary to paraproteinemias	5 (83%)

Which has a better prognosis?

— Kenar Jhaveri (@kdjhaveri) November 29, 2017

One study from the Mayo Clinic found 31% of patients with C3GN had a paraprotenemia. Bone marrow biopsy revealed a diagnosis of monoclonal gammopathy of undetermined significance (MGUS) in 90% of these patients, whereas 10% were diagnosed with low-grade chronic lymphocytic leukemia (CLL). No outcome data was reported. Another study of patients with DDD from the same institution found 71.4% of the patients. All had MGUS at the time of diagnosis, but one patient progressed to MM at 120 months of follow-up. These results are similar to those from the University of Utah, which found 83% of the patients with C3G over the age of 49, had an monoclonal gammopathy. In this cohort, 40% had multiple myeloma (MM) or smoldering MM, 40% had monoclonal gammopathy of renal significance (MGRS), and 10% had polyclonal plasmacytosis. The data was mixed regarding outcomes in that small study.

Chavet et al recently in Blood 2017 reported the outcomes of 50 patients with C3G and monoclonal gammopathy treated after treatment. The patients were divided into groups based on the treatment received: clone-directed therapy (alkylator or bortezomib [or rituximab for CLL]), immunosuppressive therapy (corticosteroids, cyclophosphamide, rituximab, mycophenolate, and azathioprine), or RAS inhibition. In this study clone-directed therapy produced superior renal survival than immunosuppressive and RAS inhibition therapy. No differences in patient survival were noted.  The differences in hematological response helped explain why renal response was superior in patients treated with clone-directed therapy. Only 5% of patients treated with immunosuppressive or RAS inhibition therapy achieved a very good partial response (VGPR) or better vs 31% of patients treated with clone-directed therapy. In fact, 95% of the patients treated with immunosuppressive or RAS inhibition therapy had no hematological response. The authors were also able to show renal function was only preserved in patients who achieved a VGPR or better, similar to other MGRS-associated kidney diseases.

While idiopathic C3GN and C3GN associated with MGUS have not been directly compared, based on the large study by Chavet et al, we can expect the outcomes to be better when there was an MGUS associated with the C3GN and the clone was treated. If you have a secondary cause, fix it and the kidney improves!