[Case of nephrotic syndrome due to AL-type primary amyloidosis associated with renal cell carcinoma].
ABSTRACT An 80-year-old man was admitted because of appetite loss, mild proteinuria, and leg edema. A computed tomography examination revealed a tumor in his left kidney, and a left nephrectomy was performed. The tumor was histologically diagnosed as a clear cell type renal cell carcinoma, and hematoxylin eosin staining of the non-tumor region of the resected kidney showed an almost normal morphology. Three months later, he was readmitted because of the development of nephrotic syndrome with a urinary protein excretion of 4.2 g/day, a serum total protein concentration of 5.0 g/dL, a serum albumin concentration of 2.4 g/dL, a serum total cholesterol concentration of 214 mg/dL, and generalized edema. A full examination revealed no evidence of metastasis or recurrence of the renal cell carcinoma or any other malignant tumor. Congo red staining and immunohistochemical staining were performed using the non-tumor region of his resected kidney, and the presence of amyloid deposits in the microvascular walls and glomeruli that did not disappear when treated with potassium permanganate was disclosed. In this manner, the patient was diagnosed as having AL-type primary amyloidosis. Bence-Jones proteinuria and gastric amyloidosis were also observed, but a bone marrow examination showed no signs of multiple myeloma. Previous studies have reported an association between renal cell carcinoma and renal amyloidosis, mainly AA-type secondary amyloidosis. To our knowledge, only two cases of renal cell carcinoma associated with primary amyloidosis have been previously reported. Therefore, the present patient not only represents a rare case of renal cell carcinoma associated with primary amyloidosis, but also reminds us that careful histological examination of the non-tumor region of the resected kidney is needed to evaluate the proteinuria associated with renal cell carcinoma, particularly in elderly patients.