Nephritic Syndrome
Nephritic syndrome is a disorder of glomeruli characterized by tissue swelling (edema), high blood pressure, and the presence of red blood cells in the urine.
Nephritic syndrome can develop suddenly or over a short time period (acute nephritic syndrome) or develop and progress slowly (chronic nephritic syndrome). In 1% of children and 10% of adults, the acute nephritic syndrome evolves into rapidly progressive glomerulonephritis, in which most of the glomeruli are destroyed, resulting in kidney failure.
Causes
Acute nephritic syndrome most often results from infection by streptococcus, a type of bacteria. Acute nephritic syndrome after a streptococcal infection (post-streptococcal glomerulonephritis) typically develops following a throat or skin infection in children between the ages of 2 and 14. Infections by other types of bacteria, such as staphylococcus and pneumococcus, viral infections such as chickenpox, and parasitic infections such as malaria can also result in acute nephritic syndrome. Membranoproliferative glomerulonephritis, IgA nephropathy, Henoch-Schönlein purpura, systemic lupus erythematosus, mixed cryoglobulinemia, Goodpasture's syndrome, and Wegener's granulomatosis are all noninfectious causes of acute nephritic syndrome. Acute nephritic syndrome that develops into rapidly progressive glomerulonephritis most often results from conditions that involve an abnormal immune reaction.
The cause of chronic nephritic syndrome cannot be identified in many people. Often, chronic nephritic syndrome seems to result from one of the same conditions that causes acute nephritic syndrome.
Symptoms
About half of the people with acute nephritic syndrome have no symptoms. If symptoms do occur, the first to appear are fluid retention and tissue swelling (edema), low urine volume, and dark urine that contains blood. Edema may first appear as puffiness of the face and eyelids but later is prominent in the legs. Blood pressure increases as kidney function becomes impaired. In turn, high blood pressure and swelling of the brain may produce headaches, visual disturbances, and more serious disturbances of brain function. In older people, nonspecific symptoms, such as nausea and a general feeling of illness (malaise), are more common.
When rapidly progressive glomerulonephritis develops, weakness, fatigue, and fever are the most obvious early symptoms. Loss of appetite, nausea, vomiting, abdominal pain, and joint pain are also common. About 50% of people had a flu-like illness in the month before kidney failure started to develop. These people have edema and usually produce very little urine. High blood pressure is uncommon and rarely severe when it does occur.
Because chronic nephritic syndrome usually causes only very mild or subtle symptoms for years, it goes undetected in most people. Fluid retention (edema) may occur. High blood pressure is common. The disease may progress to kidney failure, which can cause itchiness, fatigue, decreased appetite, nausea, vomiting, and difficulty breathing.
Diagnosis
Doctors investigate the possibility of acute nephritic syndrome in people who develop symptoms of the disorder after having had strep throat or another infection and whose laboratory test results indicate kidney dysfunction. Laboratory tests show variable amounts of protein and blood cells in the urine and a high concentration of urea and creatinine (metabolic waste products) in the blood.
In people with rapidly progressive glomerulonephritis, protein clumps (casts) of red blood cells or white blood cells are almost always visible under a microscope, and blood tests detect anemia and often an abnormally high number of white blood cells. When doctors suspect nephritic syndrome, a biopsy is usually performed to confirm the diagnosis, help determine the cause, and determine the amount of scarring and potential for reversibility.
Additional tests are sometimes helpful for identifying the cause of nephritic syndrome. For example, a throat culture may provide evidence of streptococcal infection. Blood levels of antibodies against streptococci may be higher than normal or progressively increase over several weeks. Acute nephritic syndrome that follows an infection other than strep throat is usually easier to diagnose, because its symptoms often begin while the infection is still obvious. Cultures and blood tests that help identify the organisms that cause these other types of infections are sometimes needed to confirm the diagnosis.
Chronic nephritic syndrome develops gradually, and therefore, a doctor may not be able to tell exactly when it began. It may be discovered when a urine test performed as part of a medical examination reveals the presence of protein and blood cells in a person who is feeling well, has normal kidney function, and has no symptoms. A kidney biopsy is the most reliable way to distinguish chronic nephritic syndrome from other kidney diseases. A biopsy, however, is rarely performed in advanced stages, when the kidneys are shrunken and scarred, because the chance of obtaining specific information about the cause is small.
Prognosis
Acute nephritic syndrome resolves completely in about 80 to 90% of children and about 60% of adults.
The prognosis for people with rapidly progressive glomerulonephritis depends on the severity of glomerular scarring and whether the underlying cause, such as infection, can be cured. In about half of the people who are treated early (within weeks to a few months), kidney function is preserved and dialysis is not needed. However, because the early symptoms can be subtle and vague, many people who have rapidly progressive glomerulonephritis are not aware of the underlying disease and do not seek medical care until kidney failure develops. People with advanced kidney failure die within a few weeks unless they undergo dialysis. The prognosis also depends on the cause, the person's age, and any other diseases the person might have. When the cause is unknown or the person is older, the prognosis is worse.
In some children and adults who do not recover completely from acute nephritic syndrome, other types of kidney disorders develop, such as asymptomatic proteinuria and hematuria syndrome or nephrotic syndrome. Other people with acute nephritic syndrome, especially older adults, develop chronic nephritic syndrome.
Treatment
No specific treatment is available in most cases of acute nephritic syndrome. Following a diet that is low in protein and sodium may be necessary until kidney function recovers. Diuretics may be prescribed to help the kidneys excrete excess sodium and water. High blood pressure needs to be treated.
When a bacterial infection is suspected as the cause of acute nephritic syndrome, antibiotics are usually ineffective because the nephritis begins 1 to 6 weeks (average, 2 weeks) after the infection. However, if a bacterial infection is still present when acute nephritic syndrome is discovered, antibiotic therapy is started. Antimalarial drugs may be beneficial if the cause of the syndrome is malaria.
For rapidly progressive glomerulonephritis, drugs to suppress the immune system are started promptly. High doses of corticosteroids are usually given intravenously for about a week, followed by a variable period of time when they are taken by mouth. Cyclophosphamide, an immunosuppressant, may also be given. In addition, plasmapheresis is sometimes used to remove antibodies from the blood. If treatment is delayed, there is an increased likelihood of kidney failure and the need for dialysis. Kidney transplantation is sometimes considered for people who have chronic kidney failure, but rapidly progressive glomerulonephritis may recur in the transplanted kidney.
Angiotensin-converting enzyme (ACE) inhibitors often slow progression of chronic nephritic syndrome. Taking drugs to reduce high blood pressure and reducing sodium intake are considered beneficial. Restricting the amount of protein in the diet is modestly helpful in reducing the rate of kidney deterioration. Kidney failure must be treated with dialysis or a kidney transplant.
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