Monoclonal immunoglobulin deposition disease associated with membranous features

Background. Very few cases of non-organized and non-Randall-type monoclonal immunoglobulin deposition disease (MIDD) associated with membranous features have been reported. Information on clinicopathological features and prognosis in this entity is limited. Methods. We reviewed 5443 renal biopsies processed at our department, and identified three patients with MIDD associated with membranous features. We evaluated clinicopathological features and outcomes in these patients. Results. All patients had proteinuria, and one patient developed nephrotic syndrome. Renal insufficiency was not observed. Cryoglobulin or monoclonal protein in serum and urine was not detected. A renal biopsy showed thickening of the glomerular capillary walls and spike formation. Tubulointerstitial and vascular alterations were mild or absent. Immunofluorescence studies revealed granular IgG3-κ deposits in two patients and IgG1-κ deposits in one patient, along the glomerular capillary walls. Immunofluorescence studies using antibodies specific for γ-heavy chain Fab containing CH1 domain, CH2 domain and CH3 domain did not show any apparent deletion. On confocal microscopy, glomerular colocalization of light and heavy chains was observed. Electron microscopy showed predominant subepithelial granular deposits without distinct ultrastructural organization. All patients were treated with steroids, and good effects were observed. A follow-up renal biopsy performed in one patient showed histological improvements. No patient developed myeloma or other haematological malignancy during the course of follow-up (mean 44 months). Conclusions. MIDD associated with membranous features is an extremely rare but distinctive entity. Our study suggests glomerular deposition of a nondeleted whole immunoglobulin molecule. Patients with this entity appear to respond well to steroid therapy.