Primary membranous nephropathy is a type of kidney disease that affects the natural filtration process, resulting in excess protein output. When left untreated, kidney failure may develop.

Membranous nephropathy is a kidney condition that develops when inflammation causes you to lose too much protein through your urine (proteinuria).

When it develops for an unknown reason, other than infections or other conditions, it is known as primary membranous nephropathy (PMN). Experts think that about 80% of membranous nephropathy cases are primary.

Also known as primary membranous glomerulonephritis, PMN is both an autoimmune disorder and a glomerular disease.

Glomerular diseases affect the glomeruli in your kidneys — clusters of blood vessels that filter waste from your blood and create urine. PMN specifically affects the glomerular basement membranes, which block proteins from entering the urine.

As PMN causes a large amount of protein to leak into your urine, it’s a cause of nephrotic syndrome.

Overall, PMN is a rare condition that mostly affects adults. It can also be a serious condition that can lead to potentially life threatening complications if left untreated.

The exact cause of PMN is unknown. Like other autoimmune diseases, membranous nephropathy involves your immune system attacking your own cells and tissues.

PMN may cause the glomeruli to thicken due to inflammation. When this happens, the membrane cannot filter fluids and wastes as it should, causing the release of unusually large amounts of protein in your urine.

Like other types of glomerular diseases, PMN may develop from a combination of genetic and environmental factors.

Possible symptoms of PMN include:

  • edema (swelling)
  • unexplained weight gain
  • unusual fatigue

Symptoms of PMN tend to develop gradually over time.

Additionally, a doctor may see signs that may point to a kidney problem, such as:

When left untreated, PMN may lead to kidney failure.

Other possible complications associated with this condition include:

Aside from observing symptoms, doctors may diagnose PMN with the following tests:

  • blood testing to measure your cholesterol and protein levels
  • a urine sample to look for proteinuria
  • a glomerular filtration rate test, which determines whether your kidneys are filtering wastes as they should
  • a kidney biopsy to look for the presence of certain antibodies that may point to membranous nephropathy

If a doctor doesn’t believe your condition is secondary to any infections, health conditions, or medications, they may provide you with a PMN diagnosis.

Treatment for PMN focuses on reducing your immune system’s attack on glomerular basement membranes while also alleviating symptoms. This can involve taking immunosuppressant drugs.

However, immunosuppressants can also cause several unwanted side effects. As such, a doctor may only want you to take them when your condition is in an “active” phase and not during periods of symptom remission.

Supportive care for this condition may include:

Treatment for PMN can also help slow down its progression to kidney failure.

PMN is “idiopathic,” meaning the exact underlying cause is unknown.

Possible risk factors for secondary forms of membranous nephropathy include:

If a doctor believes any of these caused membranous nephropathy, they will likely diagnose a secondary and not a primary form of this condition.

While anyone may develop membranous nephropathy, it’s most common in white males and people between the ages of 50 and 60 years.

The exact outlook for people with PMN is difficult to predict, but it is highly treatable.

Not only is the underlying cause unknown, but an estimated one-third of people with membranous nephropathy experience spontaneous remission.

Left untreated, PMN may increase your risk of developing kidney failure. Experts also estimate that about one-third of people may experience progression to end stage kidney (renal) disease or fatal cardiovascular or thrombotic events, like heart attack or stroke.

If you do develop kidney failure, you may require dialysis or a kidney transplant. However, not everyone with this condition will develop kidney failure.

Researchers also believe that the use of immunosuppressant drugs can improve the overall outlook of this condition and reduce the need for a kidney transplant.

How common is primary membranous nephropathy?

Experts think PMN is relatively rare, affecting less than 5,000 U.S. adults.

What is the survival rate for primary membranous nephropathy?

When treated, the overall survival rate for PMN is high.

For unknown reasons, about 30% of people with this condition may achieve spontaneous remission without treatment. However, about one-third of people with PMN may develop end stage kidney disease within 10 years.

Is there a cure for primary membranous nephropathy?

There’s currently no known cure for PMN. Treatment aims to reduce inflammation and the rate of kidney function loss while also decreasing related symptoms.

PMN is a rare condition that causes inflammation in the glomerular basement membrane. This can cause reduced kidney filtration and protein to leak into the urine.

If you’re experiencing any unusual symptoms, such as edema or foamy urine, it’s important to see a doctor. They can determine whether you have PMN or another condition and possibly start treatment.

If you’ve already received a diagnosis of PMN, it’s important to see a doctor for regular visits. They can help monitor any changes and adjust your treatment plan as appropriate to help prevent further kidney damage.