Thrombotic microangiopathy with intraglomerular IgM pseudothrombi in Waldenström macroglobulinemia and IgM monoclonal gammopathy

C3 glomerulonephritis associated with monoclonal gammopathy: a retrospective case series study from a single institute in China

Objective

To investigate the demographic and clinicopathological features and renal outcomes of Chinese patients with C3 glomerulonephritis in the setting of monoclonal gammopathy.

Methods

Patients with renal biopsy-proven C3 glomerulonephritis and detectable serum and/or urine monoclonal immunoglobulin from 2006 to 2018 in Peking University First Hospital were included, their clinical data, renal pathology type, treatment, and prognosis were collected and analyzed.

Results

Nineteen patients were enrolled, accounting for 24% of C3GN patients in the study period. The mean age of onset was 55 years old and the gender ratio was 4/15 (female/male). The mean eGFR at biopsy was 49.55 ± 29.81 ml/min/1.73m². The prominent clinical manifestations included nephrotic syndrome (58%), anemia (68%), microscopic hematuria and leukocyturia (58%), and hypocomplementemia (13, 68%). The IgG was the most common isotype of monoclonal Ig on immunofixation electrophoresis. Kidney biopsies revealed a relatively prominent MPGN pattern. Only two patients had direct evidence of monocle immunoglobulins acting as C3GN pathogenic factors. Two patients had concurrent TMA-like renal injuries. The median renal survival was 12 and 15 months, respectively in patients receiving conservative therapy and immunosuppressant therapy, without statistical significance. The efficacy of clone-targeted therapy needed further investigation. Plasma exchange therapy only improved one patient’s renal outcome.

Conclusions

This is the first case series report of C3GN combined with monoclonal Ig in northern China. The renal prognosis of these patients is poor, and immunosuppressant therapies show no advantage over supportive therapy in renal prognosis, while the benefit of clone-targeted chemotherapy is still requiring investigation.

Types of M protein and clinicopathological profiles in patients with monoclonal gammopathy of renal significance

BACKGROUND

The development of renal disease in patients with monoclonal gammopathy of renal significance (MGRS) depends on the pathogenicity of the secreted monoclonal protein (M protein). However, the correlation between the types of M proteins and clinical and renal pathological features is still unclear.

METHODS

A total of 148 patients with detectable serum M protein and biopsy-proven MGRS were recruited. The patients were categorized according to the heavy and light chain types of M protein in the serum.

RESULTS

Among 148 patients, the most common M protein was IgGλ, followed by IgAλ and IgGκ. According to the type of heavy chain, patients with IgM-MGRS were more likely to have renal dysfunction, anemia and hypocomplementemia than patients with IgG-MGRS and IgA-MGRS. The λ light chain was predominant in patients with IgG-MGRS and IgA-MGRS, whereas the κ light chain was predominant in patients with IgM-MGRS. The most common renal lesion was amyloidosis in patients with IgG-MGRS and IgA-MGRS, while it was cryoglobulinemic glomerulonephritis in patients with IgM-MGRS. According to the type of light chain, patients with κ light chain were more likely to be male and to have renal dysfunction, anemia and hypocomplementemia than those with λ light chain. The types of heavy chain and light chain of M protein were not associated with patient or renal survival.

CONCLUSION

The clinicopathological features were distinct in patients with different types of M protein. Integration of the types of M protein and renal pathologic findings may shed light on individual management of patients with MGRS.