Membranous nephropathy

Definition

Membranous nephropathy is a kidney disorder which involves changes and inflammation of the structures inside the kidney that help filter waste and fluids. The inflammation leads to problems with kidney function.

Alternative Names

Membranous glomerulonephritis; Membranous GN; Extramembranous glomerulonephritis; Glomerulonephritis - membranous; MGN

Causes, incidence, and risk factors

Membranous nephropathy is caused by thickening of part of the glomerular basement membrane. Glomerular basement membrane is a part of the kidneys that helps filter waste and extra fluid from the blood. The exact reason for this thickening is not known.

It is one of the most common causes of nephrotic syndrome. The condition may be a primary kidney disease of uncertain origin, or it may be associated with other conditions.

The following increase your risk for this condition:

• Exposure to toxins, including gold and mercury
• Use of certain medicines, including penicillamine, trimethadione, and skin-lightening creams
• Infections, including hepatitis B, malaria, syphilis, and endocarditis
• Blood cancers, including non-Hodgkin lymphoma and leukemia
• Melanoma, a type of skin cancer
• Systemic lupus erythematosus, rheumatoid arthritis, Graves' disease, and other autoimmune disorders

The disorder occurs in approximately 2 out of 10,000 people. It may occur at any age but is more common after age 40.

Symptoms

• Edema (swelling) in any area of the body
• Foamy appearance of urine
• Weight gain
• Poor appetite
• Urination, excessive at night
• High blood pressure
• Fatigue

Signs and tests

A physical exam may show swelling (edema).

A urinalysis may reveal protein in the urine or blood in the urine. Glomerular filtration rate (the "speed" of blood purification) is usually nearly normal.

Other tests may be done to see how well the kidneys are working. These include:

• Blood urea nitrogen (BUN)
• Creatinine - blood
• Creatinine clearance

Albumin levels in the blood may be low. Cholesterol and triglyceride levels may be high.

Kidney biopsy confirms the diagnosis of membranous nephropathy.

The following tests can help determine the cause of membranous nephropathy:

• Antinuclear antibodies test
• Anti-double-strand DNA, if the antinuclear antibodies test is positive
• Blood tests to check for hepatitis B, hepatitis C, and syphillis
• Complement levels
• Cryoglobulin test

Treatment

The goal of treatment is to reduce symptoms and slow the progression of the disease.

Controlling blood pressure is the most important measure to delay kidney damage. The goal is to keep blood pressure at or below 130/80 mmHg. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) are the medicines most often used.

Corticosteroids and other drugs that suppress or quiet the immune system may be used.

High blood cholesterol and triglyceride levels should be treated to reduce the risk of atherosclerosis. However, a low-fat, low-cholesterol diet is usually not as helpful for people with membranous nephropathy. Medications to reduce cholesterol and triglycerides may be recommended, most commonly statins.

A low salt diet may help with swelling in the hands and legs. Water pills or diuretics may also help with this problem.

Low protein diets may or may not be helpful. A moderate-protein diet (1 gram of protein per kilogram of body weight per day) may be suggested.

Vitamin D may need to be replaced if nephrotic syndrome is chronic and does not respond to therapy.

This disease increases the risk for blood clots in the lungs and legs.Patients are occasionally prescribed blood thinners to prevent these complications.

Expectations (prognosis)

The outlook varies. There may be symptom-free periods and acute flare ups. In some cases, the condition may go away with or without therapy.

The majority of patients will have some degree of irreversible kidney damage within 2-20 years. About 20% of those will progress to end-stage renal disease.

Complications

• Nephrotic syndrome
• Chronic renal failure
• End-stage renal disease
• Renal vein thrombosis
• Pulmonary embolism

Calling your health care provider

Call for an appointment with your health care provider if symptoms indicate membranous nephropathy may be present. Call for an appointment with your health care provider if symptoms worsen or persist, if you experience a decreased urine output or other new symptom develops.

Prevention

Promptly treating associated disorders and avoiding associated substances may reduce risk.

References

In: Brenner BM, ed. Brenner: Brenner and Rector's the Kidney. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 30.