Membranous nephropathy is a pathomorphologic diagnostic term, which is a common cause of adult nephrotic syndrome characterized by the characteristic pathologic changes of massive immune complex deposition visible on the epithelial side of glomerular capillary collaterals. Clinical manifestations include nephrotic syndrome (massive proteinuria, hypoproteinemia, high edema, hyperlipidemia), or asymptomatic, non-nephrotic range of proteinuria.
Membranous nephropathy can be classified into idiopathic and secondary membranous nephropathy depending on the causes.
1. Idiopathic membranous nephropathy
Mostly it is associated with antiphospholipase A2 receptor antibodies, which are bound to the corresponding antigen on the podocyte to form an in situ immune complex, followed by activation of complement via the bypass pathway to form a C5b-9 membrane attack complex, damaging the podocyte, disrupting the glomerular filtration barrier, and producing proteinuria.
2. Secondary membranous nephropathy
It is a disease secondary to many systemic diseases, such as systemic lupus erythematosus, rheumatoid arthritis, hepatitis B virus infection as well as drugs, toxins, tumors or environmental factors, etc. The main drugs giving rise to secondary membranous nephropathy are some gold agents, mercury, penicillamine, ibuprofen, diclofenac, etc.
It is more commonly seen in people over 40 years of age and tends to be more insidious in its onset.
2. Nephrotic syndrome
Clinical manifestations include nephrotic syndrome (massive proteinuria, hypoproteinemia, high edema, hyperlipidemia), or asymptomatic, non-nephrotic range of proteinuria.
3. Microscopic hematuria
It may be associated with a small amount of microscopic hematuria.
4. Hypertension and/or renal impairment
Some patients are associated with hypertension and/or impaired renal function.
5. Physical signs
Edema of both lower extremities or face, and in severe cases, there may be pneumoperitoneum and pleural effusion, mostly leakage; some patients may be without clinical symptoms and proteinuria is found during routine physical examination.