Glomerulonephritis is a histopathologic diagnosis acutely associated with clinical findings of hematuria, edema, and hypertension. It commonly follows a skin or throat infection caused by nephritogenic strains (serotypes 12 and 49) of group A β-hemolytic streptococcus (serotypes 12 and 49) in children between 3 and 7 years of age, with males being more commonly affected. Viral infections such as cytomegalovirus and coxsackievirus have also been implicated. Patients younger than 2 years are rarely affected. Timely treatment of pharyngitis does not clearly decrease the incidence of acute glomerulonephritis.

Glomerulonephritis probably results from the deposition of circulating immune complexes in the kidney. These immune complexes are deposited on the basement membrane, causing glomerular inflammation and injury and thereby reducing glomerular filtration.¹

DIAGNOSTIC FINDINGS

There is usually a preceding streptococcal infection or exposure 1 to 2 weeks before the onset of glomerulonephritis. An interval of less than 4 days may imply that the illness is an exacerbation of pre-existing disease rather than an initial attack. Skin infections may have a latent period of 3 to 6 weeks. Henoch–Schönlein purpura, nephritis associated with subacute bacterial endocarditis, or shunt infection may also be causative. Fever, malaise, abdominal pain, and decreased urine output are often noted.

The physical findings reflect the duration of illness. Initial findings may be mild facial or extremity edema only, with a minimal rise in blood pressure. Patients uniformly develop fluid retention and edema and commonly have hematuria (90%), hypertension (60%–70%), and oliguria (80%). Fever, malaise, and abdominal pain are frequently reported. Anuria and renal failure occur in 2% of children. Circulatory congestion as well as hypertensive encephalopathy may be noted.

Urinalysis reveals microscopic or gross hematuria. Erythrocyte casts are present in 60% to 85% of hospitalized children. Proteinuria is generally less than 2 g/m² per 24 hours. Hematuria (Fig. 88-1) and proteinuria (Fig. 88-2) may present independently and require a specific evaluation.^2–4 Leukocyturia and hyaline and granular casts are common. If the diagnosis and etiology are unclear, renal biopsy may be indicated to exclude other diagnoses.

The fractional excretion of sodium as a reflection of renal function may be reduced (Table 88-1). The blood urea nitrogen (BUN) level is elevated disproportionately to the creatinine level.

Total serum complement, and specifically C3, is reduced in 90% to 100% of children during the first 2 weeks of illness, returning to normal within 4 to 6 weeks. Ongoing low levels suggest the presence of chronic renal disease. The streptozyme test, measuring five different streptococcal antibodies, is positive in 95% of patients with pharyngitis and 80% of those with skin infections. The antistreptolysin (ASO) level may be low or negative in patients with skin infections. Anemia, hyponatremia, and hyperkalemia may be present.

MANAGEMENT

Fluid and salt restriction is essential to normalize intravascular volume. Diuretics are often required. Elevated blood pressure may require specific pharmacologic management. Specific complications, such as congestive heart failure, renal failure, and hyperkalemia, must be anticipated and treated. Recovery is usually complete. More than 80% of patients recover without residual renal damage.⁵ Children without evidence of hypertension, congestive heart failure, or azotemia may be followed closely at home, although a nephrologist is usually consulted. Fortunately, recurrence is rare.

Historically known as lipoid nephrosis, childhood nephrosis, foot process disease, nil disease, minimal change nephrotic syndrome, and idiopathic nephrotic syndrome; nephrotic syndrome is associated with increased glomerular permeability, which produces massive proteinuria. Hypoalbuminemia results, producing a decrease in the plasma osmotic pressure. The shift of fluids from the vascular to interstitial spaces shrinks the plasma volume, thereby activating the renin–angiotensin system and enhancing sodium reabsorption and edema develops.

The etiology is generally idiopathic, but has been associated with diffuse foot process effacement on electron microscopy with glomerular lesions Seventy-five percent of children have minimal change disease. Intoxications, allergic reactions, infection, and other entities have also been associated with the syndrome (Table 88-2). It may be a primary pathologic process or associated with a systemic disease.