Nephritic syndrome

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Not to be confused with nephrotic syndrome

Nephritic syndrome (or acute nephritic syndrome)^[1] is a collection of signs (known as a syndrome) associated with disorders affecting the kidneys, more specifically glomerular disorders. ^[2] It's characterized by having small pores in the podocytes of the glomerulus, large enough to permit proteins (proteinuria) and red blood cells (hematuria) to pass into the urine. By contrast, nephrotic syndrome is characterized by only proteins (proteinuria) moving into the urine. Both nephritic syndrome and nephrotic syndrome result in hypoalbuminemia due to protein albumin moving from the blood to the urine.

Hematuria can be caused by bleeding anywhere in the urinary tract, but if the RBCs are trapped in urinary casts, it is more likely that the bleeding originated in the nephron, and Nephritic syndrome becomes more probable.

It is usually distinguished from nephrotic syndrome, but sometimes the two are described as associated in a minority of cases.^[3] Some conditions can cause either syndromes, and both syndromes can have a similar appearance upon biopsy. Neither term represents a definitive diagnosis, but both terms can be useful in the early stages of a differential diagnosis.

Signs and symptoms

Nephritic syndrome is characterized by;

• hematuria (blood in the urine), with red blood cell (RBC) casts present in the urine
• proteinuria (protein in the urine) - small amounts of protein are lost in the urine, but this is usually trivial (<3.5 g/day)
• hypertension^[4] (high blood pressure)- mild
• uremia - due to retention of waste products

and variable renal insufficiency, with;

• azotemia (elevated blood nitrogen)
• oliguria (low urine output <400 mL/day)

The main features are hypertension and RBC casts. The proteinuria in nephritic syndrome is not usually severe, but may occasionally be heavy enough to be in the range usually found in nephrotic syndrome.

Mnemonic: PHAROH = Proteinuria, Hematuria, Azotemia, RBC casts, Oliguria, Hypertension

Diagnosis

Nephritic syndrome is not a specific diagnosis. It is a clinical syndrome and characterized by the above signs.

An anti-streptolysin O titre (or ASOT) is typically done to test for exposure to streptococci. This test however has incredibly poor specificity.

The test panel of choice nowadays is ASOT combined with an anti-DNAase B test, the latter have approximately 90% sensitive.

Pathophysiology

The exact pathophysiology is dependent on the specific diagnosis. However, the common features are an inflammation of the glomeruli, leading to salt and water retention (causing hypertension) and a reduction in the kidney function.

Differential diagnosis

The two classic diagnoses of nephritic syndrome are:

• post-streptococcal glomerulonephritis
• crescentic glomerulonephritis (also called rapidly progressive glomerulonephritis)

Nephritic syndrome causes are usually grouped into 'focal proliferative' and 'diffuse proliferative' on the basis of histology (obtained by a renal biopsy).

Focal proliferative

• IgA nephropathy
• chronic liver failure
• Celiac sprue
• dermatitis herpetiformis
• Henoch-Schoenlein purpura
• Alport syndrome
• SLE

Diffuse proliferative

• membranoproliferative glomerulonephritis (malaria, hepatitis B, hepatitis C, chronic infection, sickle-cell disease, SLE, hemolytic uremic syndrome/thrombotic thrombocytopenic purpura)
• cryoglobulinemia
• SLE
• rapidly progressing glomerulonephritis (RPGNs) - several.

Treatment

Treatment is dependent on the underlying etiology (cause) and the degree of kidney dysfunction.

Prognosis

Because nephritic syndrome is not a disease, just a collection of symptoms, the prognosis depends on the underlying etiology.

References

External links

• Acute nephritic syndrome - medlineplus.org
• Nephritic syndrome - A to Z topics.
• Nephritic syndrome - Merck Manual.