IgG-type lymphoplasmacytic lymphoma with light chain deposition disease.

Lymphoplasmacytic lymphoma (LPL) is a rare, indolent B-cell malignancy, with the IgG subtype being particularly uncommon. We present a case of IgG-type LPL complicated by kidney dysfunction due to light chain deposition disease (LCDD), representing the first documented instance of LCDD-related kidney impairment in this lymphoma subtype. A 65-year-old man presented with lower extremity edema and was found to have significant kidney dysfunction. Laboratory tests revealed elevated serum creatinine, heavy proteinuria, and a markedly skewed free light chain κ/λ ratio. Immunofixation electrophoresis identified an IgG-κ monoclonal protein and Bence Jones protein (κ light chain). Bone marrow biopsy confirmed LPL with a MYD88 L265P mutation, while kidney biopsy demonstrated mesangial proliferation, interstitial fibrosis, and granular κ light chain deposits consistent with LCDD. Given the rarity of IgG-type LPL with kidney involvement, this case underscores the importance of a thorough diagnostic workup in patients presenting with both hematologic malignancy and kidney dysfunction. Early recognition and appropriate management are critical for improving patient outcomes. As non-IgM LPL cases have historically been associated with poorer prognoses compared to Waldenström macroglobulinemia, the identification of underlying kidney complications such as LCDD is essential. Further accumulation of similar cases is needed to establish optimal treatment strategies.