Membranous nephropathy may develop gradually, so you may not suspect that anything is wrong. As you lose protein from your blood, swelling in your legs and ankles and weight gain from excess fluid can occur. Many people have lots of swelling from the very beginning of the disease, but others may not have any severe symptoms until they have advanced kidney disease.

Signs and symptoms of membranous nephropathy include:

• Swelling in the legs and ankles
• Weight gain
• Fatigue
• Poor appetite
• Urine that looks foamy
• High cholesterol
• Increased protein in the urine (proteinuria)
• Decreased protein in the blood, particularly albumin

Often, membranous nephropathy results from some type of autoimmune activity. Your body's immune system mistakes healthy tissue as foreign and attacks it with substances called autoantibodies. These autoantibodies target certain proteins located in the kidney's filtering systems (glomeruli). This is known as primary membranous nephropathy.

Sometimes membranous nephropathy is brought on by other causes. When this happens, it's called secondary membranous nephropathy. Causes may include:

• Autoimmune disease, such as lupus erythematosus
• Infection with hepatitis B, hepatitis C or syphilis
• Certain medications, such as gold salts and nonsteroidal anti-inflammatory drugs
• Solid cancerous tumors or blood cancers

Membranous nephropathy may also occur along with other kidney diseases, such as diabetic nephropathy and rapidly progressive (crescentic) glomerulonephritis.

Factors that can increase your risk of membranous nephropathy include:

• Having a medical condition that can damage your kidneys. Certain diseases and conditions increase your risk of developing membranous nephropathy, such as lupus and other autoimmune diseases.
• Use of certain medications. Examples of medications that can cause membranous nephropathy include nonsteroidal anti-inflammatory drugs and gold salts.
• Exposure to certain infections. Examples of infections that increase the risk of membranous nephropathy include hepatitis B, hepatitis C and syphilis.
• Genetic background. Certain genetic factors make it more likely that you'll develop membranous nephropathy.

Complications associated with membranous nephropathy include:

• High cholesterol. Levels of cholesterol and triglycerides are often high in people with membranous nephropathy, which greatly increases the risk of heart disease.
• Blood clots. With proteinuria, you may lose proteins that help prevent clotting from your blood into your urine. This makes you more prone to having blood clots develop in deep veins or blood clots that travel to your lungs.
• High blood pressure. Waste buildup in your blood (uremia) and salt retention can raise blood pressure.
• Infections. You're more susceptible to infections when proteinuria causes you to lose immune system proteins (antibodies) that protect you from infection.
• Nephrotic syndrome. High protein levels in the urine, low protein levels in the blood, high blood cholesterol, and swelling (edema) of the eyelids, feet and abdomen occur with this syndrome.
• Acute kidney failure. In cases of severe damage to the kidneys' filtering units (glomeruli), waste products may build up quickly in your blood. You may need emergency dialysis to remove extra fluids and waste from your blood.
• Chronic kidney disease. Your kidneys may gradually lose function over time to the point where you need dialysis or a kidney transplant.