What is membranous nephropathy (MN)?
Membranous nephropathy (MN) is an immune system condition that causes too much fluid to be retained in the body and too much protein to be lost in the urine.
MN affects around 1 in 100,000 people in the UK and is twice as common in men than women, although the reason for this is not yet known.
What are the signs and symptoms of MN?
MN develops slowly, over a number of years. Common symptoms of MN include:
- Protein in the urine (proteinuria) – this is likely to only be seen when the urine is tested by dipping a specially treated paper strip into the urine (urine dipstick), although if there is a lot of protein, the urine may look frothy.
- Swelling or puffiness (oedema) – this can develop in different parts of the body, especially around the eyes and ankles. Swelling around the eyes tends to be worse first thing in the morning and improve as the day goes on whereas ankle swelling is usually worse in the evenings. There is no pain associated with the swelling itself but if it gets very bad it can cause the skin to stretch and break which can be painful. The swelling is not an allergic reaction but is caused by the kidneys retaining too much water.
- High blood pressure – this can damage the structure of the kidney if it is not treated.
- Extreme tiredness.
What causes MN?
MN occurs when certain antibodies that are produced by the immune system to fight infections attack normal tissue by mistake. This causes the tiny filters in the kidney to malfunction and allow a protein called albumin to leak into the urine where it is wasted.
The filtering process takes place across a special membrane, which is thickened in MN due to deposits of antibody.
How is MN diagnosed?
MN is usually diagnosed between the ages of 40 and 70. Routine blood or urine tests may initially show a drop in kidney function and/or an increase in protein in the urine. A further blood test can then check for antibody levels.
A kidney biopsy can help to confirm the diagnosis, but this is not always needed.
In some cases, MN is triggered by other conditions, including certain cancers, hepatitis or rheumatoid arthritis. Screening for these conditions is likely to be carried out as part of the diagnosis.
Does MN affect other parts of the body?
MN only affects the kidneys but can result in oedema (swelling) in other parts of the body, especially around the eyes and ankles.
Does MN run in families?
MN can occasionally run in families, although no genetic basis has yet been found.
How is MN treated?
Treatment for MN is based on the perceived risk of kidney damage. If there is minimal risk, a ‘watch and wait’ approach is used for around six months. Medication is still likely to be prescribed during this time. This may include:
- angiotensin receptor blockers (ARBs) or angiotensin-converting enzyme (ACE) inhibitors to reduce the loss of protein in the urine.
- diuretics (water tablets) to help the body get rid of excess water to control any swelling.
Around one in three people with MN recover without the need for any further treatment.
If further treatment is needed, immunosuppressants medicines may be prescribed. This may include steroids to dampen the immune system.
Dialysis and/or kidney transplant may be necessary if the kidneys become damaged. MN can reoccur in the transplanted kidney.
Where can I get more information or support about MN?
For more information on MN, including its diagnosis, symptoms and treatment, visit The Edinburgh Renal Unit - Membranous nephropathy.
Publication date: 11/2023
Review date: 11/2026
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