Introduction
Membranous nephropathy (also called membranous glomerulonephritis or just plain “membranous”) is one of the most common causes of nephrotic syndrome in adults without diabetes. The term “membranous” refers to the thickening of the glomerular basement membrane when viewed under a microscope.
Membranous nephropathy usually presents with symptoms caused by the loss of protein in the urine(called proteinuria). If enough protein is lost (more than 3.5 grams per day), it is called nephrotic syndrome, which usually presents with foamy urine and swelling of the legs, abdomen, arms and face.
Most of the complications seen with membranous nephropathy are due to nephrotic syndrome. Nephrotic syndrome typically causes a lot of problems with fluid retention and swelling (edema) as well cholesterol and lipid problems. If it is severe enough, you may develop blood clots, infections or malnutrition. In some people (not everyone), the damage becomes extensive enough to cause kidney failure. This usually occurs after a number of years.
It is well known that membranous nephropathy is caused by antibodies being depositing in a particular part of the glomerulus (glomerular basement membrane and subepithial space). Although we know the “what” and the “where” of this disease, we don’t always know the “why”. If we can’t identify a cause, we call it “idiopathic” or “primary” membranous. If we can identify a disease, condition, or drug causing it, we call it “secondary” membranous.
number of kidney diseases can present with protein in the urine so a definitive diagnosis of membranous nephropathy requires getting a kidney biopsy and looking at it under a microscope. The defining characteristics on biopsy are:
- Thickening of the glomerular basement membrane (GBM)
- Immune deposits across the GBM and in the subepithelial space
- Little to know abnormal cells growing in or invading the glomerulus
Membranous nephropathy is a slow disease with a variable outcome. A significant number of people (5-30%) can have a spontaneous recovery, but they usually have a more mild form of the disease. Many people (25-40%) will undergo a spontaneous partial remission with a reduced protein loss (< 2 grams per day) and stable kidney function for an extended period of time. Unfortunately, a significant number of people will eventually develop end-stage kidney disease.
Because many people with membranous nephropathy undergo a spontaneous complete or partial remission (65%), not every patient should be treated aggressively with potentially dangerous immunosuppressive drugs. Certain factors can help identify patients that might be at risk for disease progression. Important risk factors for disease progression are the amount of protein being lost in the urine, whether there is kidney failure, and how much damage is seen with the kidney biopsy.
Treatment for membranous nephropathy includes concervative treatment of symptoms from nephrotic syndrome and aggressive treatment with immunosuppressive drugs. Since there is a good chance (65%) of undergoing a complete or partial remission within 3-4 years, people with relatively mild disease or at low risk for progression should be observed.
