A Case of Spontaneous Resolution of Secondary Membranous Nephropathy

Introduction: Membranous nephropathy (MN) is the most common cause of adult-onset nephropathy. Primary MN is characterized by the presence of antibodies to the M-type phospholipase A2 receptor (PLA 2R). The most common causes of secondary MN are infectious, autoimmune disorders, or neoplasms.Here we present a unique case of secondary MN that spontaneously resolved despite progressive primary colon malignancy. Case Description: An 82-year-old gentleman with no known history of kidney diseases presented to clinic with proteinuria. The patient’s only complaints included leg swelling and unintentional weight loss of 15-20 pounds over the previous 3 years. He was noted to have a microalbumin to creatinine ratio of 5000 mg/g. One year prior, his urine microalbumin to creatinine ratio was 57 mg/g. His serum creatinine had been 0.9 mg/dL. Work up for his proteinuria included an SPEP with immunofixation, serum free light chains, hepatitis B/C serologies, anti-PLA 2R antibody, and rheumatoid factor which were all unremarkable. Kidney biopsy revealed membranous glomerulonephritis with several globally sclerosed glomeruli. IgG subclass staining showed IgG1 predominance and absent IgG4 and PLA 2R, suggestive of secondary membranous glomerulonephritis. On electron microscopy, the immune type deposits showed a mixture of electron dance and loosened deposits suggestive of prolonged disease course. Approximately 40 to 50% of the glomeruli in the biopsy were already sclerosed globally. The patient was later evaluated for several malignancies with a CT chest/abdomen/pelvis with IV contrast and a PSA screen. Patient had been recommended to undergo a screening colonoscopy but refused. He was found to have a large right sided pulmonary nodule. Patient had undergone a bronchoscopy in 2022 with pathology showing no evidence of malignant cells. A follow up PET scan showed low level activity. Patient remained on therapy with losartan, HCTZ, and spironolactone. Several months later, the patient’s microalbumin to creatinine ratio trended to 361 mg/g, which persisted for months. He was later diagnosed via repeat colonoscopy to have primary colon cancer but proteinuria had already resolved at that time. Discussion: Resolution of secondary membranous nephropathy is not known to resolve without treatment of the suspected cause.