The glomeruli are the inner structures of the kidney that include small capillaries surrounded by membranes through which the blood is filtered to form urine. Membranous nephropathy is caused by thickening of the capillary wall of the glomerular basement membrane (the deepest membrane) by immune complexes. The cause is not known.

It is one of the most common causes of nephrotic syndrome, which is the most common presentation of the disease. It may also appear as asymptomatic excretion of protein in the urine. Glomerular filtration rate (the "speed" of blood purification) is usually nearly normal, and examination of sediment in the urine may be unremarkable or may show oval fat bodies, and hyaline, granular, and fatty casts.

Membranous nephropathy may be a primary renal disease of uncertain origin, or it may be associated with other conditions. Risks include systemic disorders such as Hepatitis B, malaria, malignant solid tumors, non-Hodgkin's lymphoma, systemic lupus erythematosus, syphilis, and others. Risks also include exposure to substances or medications, including gold, mercury, penicillamine, trimethadione, skin-lightening creams, and others.

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

• Edema (swelling) in any area of the body, may be generalized
• Foamy appearance of urine
• Weight gain (from fluid retention)
• Poor appetite
• Urination, excessive at night
• Blood pressure, high

The goal of treatment is to minimize symptoms and slow the progression of the disease. Symptoms should be treated as appropriate. Medications vary. Often, corticosteroids or immunosuppressive medications may be used to attempt to reduce symptoms and progression of the disorder, with variable results. Medications to treat symptoms may include antihypertensive and diuretic medications. Antibiotics may be needed to control infections.

Treatment of high blood cholesterol and triglyceride levels is recommended to reduce the development of atherosclerosis secondary to nephrotic syndrome. Dietary limitation of cholesterol and saturated fats may be of only limited benefit as the high levels of cholesterol and triglyceride seem to be caused by overproduction by the liver rather than excessive intake of fats. Medications to reduce cholesterol and triglycerides may be recommended.

Affected individuals are at increased risk for thrombotic (clotting) events involving the lungs (pulmonary embolisms) and legs (deep venous thromboses, often referred to as DVTs). Those affected are therefore occasionally prescribed warfarin or other blood thinners to prevent these complications.

High-protein diets are of debatable value. In many patients, reducing the amount of protein in the diet produces decrease in urine protein. In most cases, a moderate-protein diet (1 gram of protein per kilogram of body weight per day) is usually recommended. Sodium in diet (salt) may be restricted to help control edema. Vitamin D may need to be replaced if nephrotic syndrome is chronic and unresponsive to therapy.

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