Primary membranous nephropathy

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Overview

Primary membranous nephropathy (pMN) is an auto-immune disease characterized by auto-antibodies targeting podocyte antigens resulting in activation of complement and damage to the glomerular basement membrane

Symptoms

The main symptoms of MN are from excess protein in your pee due to kidney damage. This leads to water retention and other symptoms. Together, these symptoms are called nephrotic syndrome. Other than edema (swelling), other signs can include:

  • Proteinuria (foamy-looking pee due to high levels of protein in your pee).
  • High cholesterol.
  • Peeing more or less than usual.
  • Weight gain (people usually gain water weight because of the swelling).
  • Fatigue (tiredness).
  • High blood pressure.
  • Trouble breathing or shortness of breath.

Causes

Primary membranous nephropathy is an autoimmune disease, which means your body is attacking healthy cells in your body. If you have MN, your body’s immune system makes an antibody (a protein that normally helps fight infections) to a protein called the phospholipase A2 receptor (PLA2R). Instead of targeting an infection, these antibodies attack certain healthy cells in your kidney. Your kidney stops being able to filter the proteins in your bloodstream, which allows them to leak into your pee.

Having an underlying medical condition that damages your kidneys puts you at risk for secondary MN. Some examples of medical conditions include:

  • Autoimmune conditions like lupus or rheumatoid arthritis.
  • Infections like malaria, hepatitis B, hepatitis C or syphilis.
  • Cancer (especially colon or lung).
  • NSAIDs (nonsteroidal anti-inflammatory drugs) and other medications like penicillamine.
  • Exposure to mercury or other toxins.

Diagnosis

If you have any symptoms of nephrotic syndrome (like protein in your pee, swelling or decreased kidney function), your primary care provider may refer you to a nephrologist. A nephrologist is a healthcare provider who specializes in diseases and conditions of the kidneys. Your nephrologist will use several tests to confirm an MN diagnosis. These tests can include:

  • Blood test: Taking a sample of blood to measure kidney function. Specific tests include blood urea nitrogen (BUN), creatinine and albumin.
  • Glomerular filtration rate (GFR): Studying a blood sample to see the speed at which your kidneys are filtering waste.
  • Kidney biopsy: Taking a small sample of kidney tissue and sending it to a lab to see if it contains an antibody associated with MN.
  • Urine test: Measuring levels of protein and blood in your urine.

Your healthcare provider may also order tests to diagnose what’s potentially causing secondary MN. These could include tests for certain infections, an antinuclear antibody test and an anti-double stranded DNA test.

Treatment

Treatment for MN depends on the type and your symptoms. The goal of treatment is to reduce your symptoms and stop the disease from getting worse. Your healthcare provider may try one or several treatments to help you.

These treatments may include:

  • Angiotensin-converting enzyme (ACE) inhibitors: Drugs that manage high blood pressure, lower urine protein levels and help reduce inflammation in your kidneys.
  • ARBs (angiotensin receptor blockers): Medication to treat high blood pressure and kidney disease.
  • Diuretics: Medications that remove excess fluid from your body (by causing you to pee more) and lower blood pressure.
  • Cholesterol-lowering medications (statins): Medication to reduce cholesterol levels.
  • Corticosteroids: Medication to reduce inflammation and suppress your immune system (this helps it not attack your healthy cells).
  • Blood thinners: Drugs that lower your risk for blood clots.
  • Changes to your diet: Reducing salt intake and keeping your overall protein intake at a moderate level. Your healthcare provider will recommend what types of diet changes you should make.

If these treatments don’t help your symptoms, your healthcare provider may recommend immunotherapy. Immunotherapy drugs stop your immune system from producing the antibody that attacks your kidneys. Some examples of immune-suppressing medications include cyclophosphamide (Cytoxan®) and rituximab (Rituxan®).

If your kidneys show severe damage, your provider may recommend a kidney transplant.

In some people with secondary MN, treating the underlying health condition may stop kidney damage from progressing.