Secondary Membranous Nephropathy Due to Benign Tumors in 2 Young Women: A Case Report

Membranous nephropathy (MN) is one of the most common causes of adult-onset nephrotic syndrome. We describe the cases of 2 young women in their 20s presenting with nephrotic syndrome due to antiphospholipase A₂ receptor (anti-PLA₂R)-negative MN, that was found to be associated with benign tumors. Both women had no extrarenal symptoms of a connective tissue disease, infection, or malignancy. They both had been previously healthy and were not receiving treatment with any drugs. Both had MN on kidney biopsy. Biopsies were negative for PLA₂R antigen, and their serum did not demonstrate the presence of anti-PLA₂R antibodies. Both were investigated for a secondary cause on the basis of negative anti-PLA₂R serology and biopsy features supportive of secondary MN and were found to have benign tumors on radioimaging: a uterine leiomyoma and mesenteric fibromatosis, respectively. In both instances, the nephrotic syndrome remitted following resection of the tumors. To our knowledge, uterine leiomyoma and mesenteric fibromatosis have not previously been described in association with MN. These cases highlight the importance of pursuing a secondary cause of MN in patients without anti-PLA₂R antibodies in serum or PLA₂R antigen on kidney biopsy.