Membranous Nephropathy

Anatomy

The kidneys are paired organs responsible for filtering waste products and excess fluid from the blood. The structural and functional unit of the kidney is the nephron, and each kidney contains up to one million nephrons. Each nephron consists of a glomerulus—a network of tiny capillaries surrounded by Bowman’s capsule—and a system of renal tubules. Blood filtration occurs in the glomerulus, while the tubules reabsorb essential substances and secrete waste products into the urine.

Description of the Disease

Membranous nephropathy is a kidney disease characterized by the deposition of immune complexes along the glomerular basement membrane. These deposits cause inflammation and damage to the glomerular filtration barrier, making it abnormally permeable to proteins. As a result, large amounts of protein are lost in the urine.

The disease commonly presents as nephrotic syndrome, which is characterized by heavy proteinuria (more than 3.5 g of protein in the urine per day), low blood albumin levels (hypoalbuminemia), and generalized edema.

Membranous nephropathy occurs predominantly in adults and is rare in children.

Cause of the Disease

Membranous nephropathy may be primary (idiopathic) or secondary.

Primary membranous nephropathy is now recognized as an autoimmune disease in most cases, in which the immune system mistakenly produces antibodies that damage the glomerular basement membrane.

Secondary membranous nephropathy may occur in association with autoimmune diseases, chronic infections, certain malignancies, or the use of medications such as gold-containing compounds or lithium.

Symptoms

Common symptoms include:

• Swelling of the legs and other parts of the body (edema), particularly in the lower limbs.
• Weight gain due to fluid retention.
• Frequent urination at night (nocturia).
• Fatigue.
• Insomnia.
• Loss of appetite.

Diagnosis

Membranous nephropathy is suspected in patients with nephrotic syndrome or when significant proteinuria is detected during routine urine testing.

Evaluation includes blood and urine tests to assess kidney function and the degree of protein loss. Additional investigations may be performed to identify an underlying cause.

The diagnosis is confirmed by kidney biopsy, which demonstrates the characteristic thickening of the glomerular basement membrane caused by immune complex deposition.

Treatment

If an underlying cause is identified, treatment is directed at the associated disease or discontinuation of the offending medication.

Management also includes supportive therapy to reduce edema and control high blood pressure. In patients at increased risk of disease progression, immunosuppressive therapy, including glucocorticosteroids and other immunosuppressive agents, may be recommended.

Some patients experience spontaneous or treatment-induced remission, whereas others develop progressive kidney dysfunction that may eventually lead to end-stage kidney disease. In advanced cases, kidney replacement therapy, including dialysis and kidney transplantation, may become necessary.

Source | Author Doctor Nikas Samuolis, reviewed by Prof. Virginijus Šapoka | Vilnius University | Faculty of Medicine | Head of the Department of Internal Medicine, Family Medicine, and Oncology