Overview of Nephrotic Syndrome
Nephrotic syndrome (NS) is a condition that is often caused by any of a group of diseases that damage the kidneys' filtering system, the glomeruli. The structure of the glomeruli prevents most protein from getting filtered through into the urine. Normally, a person loses less than 150 mg of protein in the urine in a 24-hour period. Nephrotic-range proteinuria, the urination of more than 3.5 grams of protein during a 24-hour period, or 25 times the normal amount, is the primary indicator of NS.
Incidence and Prevalence of Nephrotic Syndrome
About two in every 10,000 people experience nephrotic syndrome. Nephrotic syndrome prevalence is difficult to establish in adults because the condition is usually a result of an underlying disease. In children, it is diagnosed in more boys than girls, usually between 2 and 3 years of age.
Nephrotic Syndrome Signs and Symptoms
In addition to proteinuria, there are three main symptoms of nephrotic syndrome associated with protein leaking into the urine:
- Hypoalbuminemia (low level of albumin in the blood)
- Edema (swelling)
- Hypercholesterolemia (high level of cholesterol in the blood)
Hypoalbuminemia is a low level of albumin (a protein) in the blood due to proteinuria. Low albumin in the blood causes fluid to move from the blood into the tissue, causing swelling. The kidney perceives the decrease of fluid in the blood and aggressively retains as much fluid and salt as it can. This contributes to the body's fluid-overload state.
Nephrotic-related swelling makes tissue puffy, soft, and impressionable to the touch. Edema is most common in the legs and feet, especially after standing all day. It can cause feelings of tightness in the extremities and may affect mobility. In later stages, swelling may occur in the abdomen (ascites), hands, and around the eyes in the morning (called periorbital edema). In later stages, the whole body may swell (anasarca). Some people gain weight after fluid builds up in their bodies for a long time.
Hypercholestrolemia, high blood cholesterol, is common in nephrotic syndrome). In addition to albumin, other important enzymes involved in cholesterol metabolism slip through the glomeruli, which contribute to high blood cholesterol.
Nephrotic Syndrome Complications
Nephrotic syndrome is associated with renal failure. The disease that causes NS can damage the glomeruli and can interfere with their ability to clean the blood. The edema that is present in the legs may also be occurring in the kidney tissue itself and can interfere with the kidneys' ability to clean the blood. Renal failure can either be gradual (CRF) or acute (ARF).
A hypercoaguable state, in which the blood abnormally overclots, is also seen in some patients with NS. This means that they are at risk for developing a blood clot in the legs or in the renal veins that transport blood from the kidney. Some patients take blood thinners to prevent this complication.
Causes of Nephrotic Syndrome
The following diseases can cause specific damage to the glomeruli and often result in the development of heavy proteinuria and in many instances NS:
- Amyloidosis (the stiffening and subsequent malfunction of the kidney due to fibrous protein deposit in the tissue)
- Congential nephrosis
- Focal segmental glomerular sclerosis (FSGS) (creates scar tissue in the glomerulus, damaging its protein-repellant membrane)
- Glomerulonephritis (GN)
- Diffuse mesangial proliferative GN (affecting the messangium)
- Membranous (damages the protein-repellant membrane)
- Postinfectious (occurs after an infection)
- IgA nephropathy (Berger's disease) (deposit of specific immunoglobulin A causing an inflammatory reaction and leading to glomerulonephritis)
- Minimal change disease (Nil's disease)
- Pre-eclampsia (rarely associated with NS, more often associated with heavy proteinuria)
Many of these diseases tend to occur more often in certain age groups:
- Less than 1 year old
- Congenital nephrosis
- Less than 15 years old
- Min change
- Age 15 to 40 years
- Min change
- Over age 40
- Membranous GN
- Diabetic nephropathy
- Over 60
- Amyloidosis may account for up to 20% of cases