Monoclonal Gammopathy of Renal Significance with Deposits of Infrequent Morphology: Two Case Reports of Light and Heavy Chain Deposition Disease with Atypical Presentation and Literature Review.

backgroundMonoclonal immunoglobulin deposition disease (MIDD) includes three entities: light chain deposition disease (LCDD), heavy chain deposition disease (HCDD) and light and heavy chain deposition disease (LHCDD). The renal presentation can manifest with varying degrees of proteinuria and/or nephrotic syndrome, microhematuria, and often leads to end-stage renal disease. Given the rarity of LHCDD, therapeutic approaches for this condition remain inconclusive, as clinical trials are limited. CASE PRESENTATION: We report two male patients with underlying monoclonal gammopathy of renal significance (MGRS) associated with LHCDD lesions. Both cases had non-nephrotic proteinuria, moderately impaired renal function, and normal levels of C3 and C4. Light microscopy of the renal biopsies in both patients did not show lesions of nodular glomerulosclerosis. Immunofluorescence showed a staining pattern with interrupted linear IgA-κ in patient #1 and IgA-λ in patient #2 only along the glomerular basement membrane (GBM). Electron microscopy of patient #1 revealed electrodense deposits in the subendothelial and mesangial areas only along the GBM. DISCUSSION: In this case series, we discuss the clinical, analytical, and histopathological findings of two rare cases of LHCDD. Both patients exhibited IgA monoclonality and were diagnosed with monoclonal gammopathy of undetermined significance (MGUS) by the hematology department at the time of renal biopsy. Treatment with steroids and cytotoxic agents targeting the clone cells responsible for the deposition disease resulted in a favorable renal and hematologic response.