A. ESSENTIALS OF DIAGNOSIS
- History of streptococcal infection
- Mild generalized edema, mild hypertension, retinal hemorrhages
- Gross hematuria; protein, erythrocyte casts, granular and hyaline casts, white blood cells (leukocytes), and renal epithelial cells in urine
- Elevated antistreptolysin O titer, hypocomplementemia
B. GENERAL CONSIDERATIONS
Poststreptococcal glomerulonephritis is a disease affecting both kidneys. In most cases recovery from the acute stage is complete, but progressive involvement may destroy renal tissue, leading to renal insufficiency. Acute glomerulonephritis is most common in children aged 3-10 years. By far the most common cause is an antecedent infection of the pharynx and tonsils or of the skin with group A betahemolytic streptococci, certain strains of which are nephritogenic. Nephritis occurs in 10-15% of children and young adults who have clinically evident infection with a nephritogenic strain.
In children under age 6, pyoderma (impetigo) is the most common antecedent; in older children and young adults, pharyngitis is a common antecedent. Occasionally, nephritis may follow infection due to other agents, hence the more general term postinfectious glomerulonephritis.
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The pathogenesis of the glomerular lesion has been further elucidated by the use of new immunologic techniques (immunofluorescence) and electron microscopy. A likely sequel to infection is injury to the mesangial cells in the intercapillary space. The glomerulus may then become more easily damaged by antigen-antibody complexes developing from the immune response to the infection.
Complement is deposited in association with IgG or alone in a granular pattern on the epithelial side of the basement membrane.
Gross examination of the involved kidney shows only punctate hemorrhages throughout the cortex. Microscopically, the primary alteration is in the glomeruli, which show proliferation and swelling of the mesangial and endothelial cells of the capillary tuft. The proliferation of capsular epithelium occurs and around the tuft there are collections of leukocytes, erythrocytes, and exudate.
Edema of the interstitial tissue and cloudy swelling of the tubular epithelium are common. When severe, typical histologic findings in glomerulitis are enlarging crescents that become hyalinized and converted into scar tissue and obstruct the circulation through the glomerulus. Degenerative changes occur in the tubules, with fatty degeneration, necrosis, and ultimately scarring of the nephron.
C. CLINICAL FINDINGS
1. Symptoms and signs– Often the disease is mild, and there may be no reason to suspect renal involvement unless the urine is examined. In severe cases, about 2 weeks after the acute streptococcal infection, the patient has headache, malaise, mild fever, puffiness around the eyes and face, flank pain, and oliguria. Hematuria is usually noted as “bloody” or, if the urine is acid, as “brown” or “coffee colored.” There may be moderate tachycardia, dyspnea, and moderate to marked elevation of blood pressure. Tenderness in the costovertebral angle is common.
2. Laboratory findings–
The diagnosis is confirmed by examination of the urine, which may be grossly bloody or coffee colored (acid hematin) or may show only microscopic hematuria. In addition, the urine contains protein (1-3+) and casts. Hyaline and granular casts are commonly found in large numbers, but the classic sign of glomerulitis, occasionally noted, is the erythrocyte cast. The erythrocyte cast is usually of small caliber, is intensely orange or red, and may show the mosaic pattern of the packed erythrocytes held together by the clot of fibrin and plasma protein.
With the impairment of renal function (decrease in glomerular filtration rate and blood flow) and with oliguria, plasma or serum urea nitrogen and creatinine become elevated, the levels varying with the severity of the renal lesion. A mild normochromic anemia may result from fluid retention and dilution. Infection of the throat with nephritogenic streptococci is frequently followed by increasing antistreptolysin O titers in the serum, whereas high titers are usually not demonstrable following skin infections. Serum complement levels are usually low.
Confirmation of diagnosis is made by examination of the urine, although the history and clinical findings in typical cases leave little doubt. The finding of erythrocytes in a cast is proof that erythrocytes were present in the renal tubules and did not arise from elsewhere in the genitourinary tract.
3. Treatment–
There is no specific treatment. Eradication of infection, prevention of overhydration and hypertension, and prompt treatment of complications such as hypertensive encephalopathy and heart failure require careful management.
4. Prognosis–
Most patients with the acute disease recover completely; 5-20% show progressive renal damage.
This damage may be evident only years after the immune injury. If oliguria, heart failure, or hypertensive encephalopathy is severe, death may occur during the acute attack.
Even with severe acute disease, however, recovery is the rule, particularly in children.
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