Heavy-chain deposition disease associated with multiple myeloma: a case report

Heavy-chain deposition disease (HCDD) is a rare disorder characterized by the deposition of monoclonal immunoglobulin. Due to the disease's rarity and diagnostic challenges, its prognosis is generally poor. Herein, we report a case of successful treatment of HCDD coexisting with multiple myeloma. A 56-year-old man presented at an outpatient clinic with complaints of whole-body pain, edema, and dyspnea that had persisted for 2 weeks. Diagnostic tests confirmed nephrotic syndrome, hematuria, and progressive renal failure. Serum immunofixation electrophoresis identified the presence of IgG kappa paraprotein. A diagnosis of multiple myeloma was established following a bone marrow biopsy. A renal biopsy revealed antibodies specific to the heavy chains of IgG on immunofluorescence, and electron microscopy showed diffuse electron-dense "powdery" densities in the glomerular basement membrane. Based on these findings, the patient was diagnosed with both HCDD and multiple myeloma. Following the diagnosis, the patient immediately began anti-plasma cell therapy using bortezomib, lenalidomide, and dexamethasone. Intermittent hemodialysis was initiated due to persistent azotemia during the diagnostic process; however, renal function improved significantly after only 1 month of therapy, allowing the discontinuation of dialysis. Early intervention with anti-plasma cell therapy, such as bortezomib, is known to improve prognosis in the early stages of the disease. This case report is presented to enhance understanding of HCDD and underscore the importance of prompt diagnosis and treatment in managing this rare condition.