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Membranous nephropathy
Definition
Membranous nephropathy is a kidney disorder that leads to changes and inflammation of the structures inside the kidney that help filter wastes and fluids. The inflammation may lead to problems with kidney function.
Alternative Names
Membranous glomerulonephritis; Membranous GN; Extramembranous glomerulonephritis; Glomerulonephritis - membranous; MGN
Causes
Membranous nephropathy is caused by the thickening of part of the glomerular basement membrane. The 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.
The thicker glomerular membrane does not work normally. Large amounts of protein are lost in the urine as a result.
This condition is one of the most common causes of nephrotic syndrome. It may be a primary kidney disease, or it may be associated with other conditions.
The following increase your risk for this condition:
- Cancers, especially lung and colon cancer
- Exposure to toxins, including gold and mercury
- Infections, including hepatitis B, malaria, syphilis, and endocarditis
- Medicines, including penicillamine, trimethadione, and skin-lightening creams
- Systemic lupus erythematosus, rheumatoid arthritis, Graves' disease, and other autoimmune disorders
The disorder occurs in about 2 out of every 10,000 people. It may occur at any age, but is more common after age 40.
Symptoms
Symptoms often begin slowly over time, and may include:
- Edema (swelling) in any area of the body
- Fatigue
- Foamy appearance of urine (due to large amounts of protein)
- Poor appetite
- Urination, excessive at night
- Weight gain
Exams and Tests
A physical exam may show swelling (edema).
A urinalysis may reveal large amounts of protein in the urine. There may also be some blood in the urine. The glomerular filtration rate (the "speed" at which the kidneys cleanse the blood) is usually nearly normal.
Other tests may be done to see how well the kidneys are working and how the body is adapting to the kidney problem. These include:
- Albumin - blood and urine
- Blood urea nitrogen (BUN)
- Creatinine - blood
- Creatinine clearance
- Lipid panel
- Protein - blood and urine
A kidney biopsy confirms the diagnosis.
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 syphilis
- 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 way 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 to lower blood pressure.
Corticosteroids and other drugs that suppress 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 triglyceride levels (most often statins) may be recommended.
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 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.
Outlook (Prognosis)
The outlook varies, depending on the amount of protein loss. Patients may have symptom-free periods and occasional flare-ups. In some cases, the condition may go away, either with or without therapy.
Most patients will have some kidney damage within 2-20 years. About 20% of those patients will progress to end-stage renal disease.
Possible Complications
- Chronic renal failure
- Deep venous thrombosis
- End-stage renal disease
- Nephrotic syndrome
- Pulmonary embolism
- Renal vein thrombosis
When to Contact a Medical Professional
Call for an appointment with your health care provider if:
- You have symptoms of membranous nephropathy
- Your symptoms get worse or don't go away
- You develop new symptoms
- You have decreased urine output
Prevention
Quickly treating disorders and avoiding substances that can cause membranous nephropathy may reduce your risk.
References
Appel GB. Glomerular disorders and nephrotic syndromes. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 122.
Nachman PH, Jennette JC, Falk RJ. Primary glomerular disease. In: Brenner BM, ed. Brenner and Rector's the Kidney. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 30.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Herbert Y Lin, MD, PhD, Nephrologist, Massachusetts General Hospital; Associate Professor of Medicine, Harvard Medical School. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
