Membranous nephropathy: what is it and what causes it?

Membranous nephropathy or membranous glomerulonephritis is a slowly progressive disease that it occurs when the blood vessels in the kidney (glomeruli) are damaged and thicken. It is a leading cause of non-diabetic nephrotic syndrome in adults and has an incidence of 8-10 cases per million population.

There are 2 variants of membranous nephropathy (MN): a primary idiopathic one (without apparent cause) and a secondary one, product of infections, neoplasms, consumption of some drugs and autoimmune pathologies. If you want to know more, keep reading.

What is membranous nephropathy?

As we have already said, membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome in adults and the elderly, as stated in the magazine updated nephrology. The incidence is estimated at 5-10 cases per million inhabitants per year and up to 85% are primary.

Membranous nephropathy is caused by the deposition of antigen-antibody complexes between the glomerular basement membrane (GBM) and podocytes, renal cells attached around the capillaries of the renal corpuscle. The complexes activate the complement system and promote membrane attachment.

This attack complex damages the epithelial cells of the glomerulus. (a region with tiny coils of capillaries in the kidney where blood is filtered and urine is produced). As mentioned, over time the blood vessels in the kidney become damaged and thicken, resulting in organ failure.

The attack complex releases proteases, cytokines and oxidizing substances, causing damage to the glomerular tissue. As a result, there is a mismatch in the ion barriers of the kidney structures and substances that should not pass in the urine, such as proteins. This condition is known as proteinuria.

Symptoms associated with membranous nephropathy

According to the portal orpha.net, The pathology usually appears between 50 and 60 years of age, with symptoms limited to the kidney. Some of the more common clinical signs are as follows:

  • Swelling in the legs and ankles: renal filtration failures cause fluid to accumulate in the body. For this reason, edemas usually appear in the lower limbs of patients.
  • Weight gain: fluid retention in the body can also cause the patient to gain weight emptythat is, it does not correspond to an increase in adipose tissue.
  • Foamy urine: foamy urine is due to the presence of protein. It is one of the first signs of nephrotic syndrome.
  • Other nonspecific symptoms are tiredness and lack of appetite.

80% of the images manifest as complete nephrotic syndrome, so the patient will notice the changes clearly and his disease can be detected promptly. Leg edema is the main reason for the consultation.

Swollen legs due to membranous neropathy.
Edema is the accumulation of fluid in the tissues. When the kidney fails, inflammation usually sets up in the legs, as well as the face.

Causes of the disease

As we have said, nephrotic syndrome is divided into 2 main clinical entities: primary and secondary. It is necessary to differentiate them when discussing their etiology.

1. Primary membranous nephropathy

As indicated Stat Pearlsprimary membranous nephropathy accounts for 75-80% of all cases. Its cause is idiopathicbut to detect it, one of the following antibodies must be present in the affected area and no other possible triggers present:

  • 70-80% of cases: antibodies against M-type phospholipase A2 receptor autoantigen (PLA2R).
  • 15-20% of cases: similar to neural epidermal growth factor (NELL).
  • 1-5% of cases: antibodies against thrombospondin.

In both cases, the antibodies bind to the body’s self-antigens and launch a targeted attack on the glomerular tissue of the kidneys. At presentation of the disease, renal function is relatively normal, but thromboembolic events gradually appear which complicate the patient’s well-being.

2. Secondary membranous nephropathy

The remaining 20-25% of cases of nephropathy can be explained by underlying pathologies. For example, infectious diseases such as hepatitis, syphilis, malaria, HIV or schistosomiasis. It is also relatively common in cancer patients or before the consumption of some drugs.

Many autoimmune diseases (such as systemic lupus erythematosus) cause NM, because the patient’s misdirected immune system can mistakenly attack the kidneys. In almost all juvenile patients with membranous nephropathy there is an underlying cause of the disease, that is, it is secondary.

Possible complications

As indicated in Research F1000Up to 30% of patients develop end-stage renal disease 5 to 15 years after symptom onset. Anyway, spontaneous remissions are observed in 35-40% of cases without any immunosuppressive treatment.

On the contrary, up to 20% of patients present an aggressive picture with very marked proteinuria which rapidly evolves towards terminal stages. When renal function declines steadily during the first 12 to 24 months, the prognosis is very poor.

The remaining 40-60% of people with membranous nephropathies evolve slowly and steadily, although if there is no spontaneous remission the picture is dangerous. Reduced or no kidney function causes end-stage nephrotic syndromes, high blood pressure, easy urinary tract infections, and blood clots.

Diagnosis of membranous nephropathy

As indicated by United States National Library of MedicineThe clearest evidence that something is wrong with the kidneys is the presence of protein in the urine (proteinuria). Proteins are essential for homeostasis of the body and for obtaining energy, therefore the kidneys are responsible for their reabsorption and prevent them from being excreted in the urine.

If usable substances are excreted through urination, it is time to suspect a pathology. A person is considered to have proteinuria when the protein content in the urine is equal to or greater than 300 milligrams in 24 hours.

Inversely proportional, reduced amounts of protein in the blood also indicate proteinuria. Other chemistry tests include blood and urine albumin, blood urea nitrogen, creatinine, and lipid panel. Anyway, what specifies the accurate diagnosis is the kidney biopsy.

After taking a sample of the patient’s kidney tissue, diffuse thickening of the capillary and glomerular basement can be observed by light microscopy. Histological staining methods can also be applied to detect antibody activity.

Doctor with a model of kidneys.
The kidneys express their malfunction in the loss of protein with urine. This is known as proteinuria.

Treatment

The goal of treatment for membranous nephropathy is reduce symptoms and prevent disease progression, as this condition has no cure. In any case, as we have said, up to 3 out of 10 patients the pathology regresses on its own without the need for a clinical approach.

Depending on the degree of proteinuria of the patient, his condition can be classified into different categories. In general, some of the drugs prescribed for the treatment of membranous nephropathy are as follows:

  • Angiotensin Converting Enzyme Inhibitors: it is a blood pressure medication that can reduce the amount of protein in your urine. Because they lower blood pressure, they make it easier for these essential biomolecules to stay in the flow.
  • diuretics: Drugs that cause excretion of water and electrolytes in the urine. Although diuretics do not cure the disease, they can help reduce swelling and edema in the lower limbs.
  • Immunosuppressive drugs: We must not forget that membranous nephropathy is an autoimmune disease. Therefore, immunosuppressive therapy may be needed to slow the damage. As indicated by UNC Renal CenterSome of the more commonly used drugs are cytoxan, rituxan and prednisone.

Finally, if the nephropathy is secondary, the most important thing is to treat the underlying cause. If it is an infection, antibiotics, antiprotozoals or retrovirals will be needed. If the cause is a tumor, the extraction of the neoplastic mass will be a priority.

Patients with membranous nephropathy cannot delay their treatment

Establishing an absolute prognosis in all cases is very difficult for this pathology. A third of patients recover on their own, 10-20% die from complications of rapid onset and the remaining percentage is maintained or gradually worsens. It’s not always known what causes the condition, but sometimes it goes away on its own.

However, in cases with a poor prognosis, diuretics, immunosuppressants and other drugs can significantly lengthen the patient’s life. Prognosis depends on each case and the rate of symptom onset.

Postmembranous nephropathy: what is it and what is the cause? first appeared on research-school

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