Expanding the pathologic spectrum of light chain deposition disease: a rare variant with clinical follow-up of 7 years.

We report an unusual histologic manifestation of light chain deposition disease in a 69-year-old female patient, who presented with nephrotic syndrome and an increased serum creatinine. The renal biopsy findings by light and electron microscopy suggested a glomerulonephritis with massive immune-complex deposition, such as lupus nephritis. However, the overall clinical scenario was inconsistent with lupus. Subsequent tests revealed multiple myeloma confirmed by bone marrow biopsy and identification of a monoclonal kappa light chain immunoglobulin by serum and urine immunoelectrophoresis and immunofixation. Additional immunohistochemistry of the first biopsy also demonstrated strong kappa light chain staining of the glomerular capillary walls and mesangium but not lambda light chain or IgG staining. The patient responded well to therapy and was asymptomatic until nearly 7 years later. A repeat biopsy revealed similar findings to the first biopsy with the addition of immunofluorescence microscopy, which confirmed the prominent kappa light chain staining of the glomeruli, tubular basement membranes, and interstitium with corresponding electron-dense deposits visualized by electron microscopy. This case represents an unusual histologic variant of light chain deposition disease, which to our knowledge has not been previously described and further expands the wide clinicopathologic spectrum within the diagnostic entity of light chain deposition disease.