Acute Postinfectious Glomerulonephritis

Acute poststreptococcal GN (APSGN) is the most common cause of APIGN in children and has a higher incidence in developing countries (Figure 62-2). APSGN is caused by nephritogenic forms of Lancefield group A streptococci. In most cases, there is clinical or laboratory evidence of antecedent streptococcal infection. APSGN must be confirmed or ruled out before looking for less common causes of post infectious GN (Staphylococcus aureus, Streptococcus viridans).

Figure 62-2 Acute poststreptococcal glomerulonephritis.

APSGN is characterized by sudden onset and variable presentation of hypertension, periorbital, lower extremity edema, oliguria, and painless gross hematuria. Urine microscopy reveals RBC casts. The glomerular damage in APSGN is immune mediated, with antigen–antibody reactions occurring in the circulation or in situ in glomeruli. These antigen–antibody reactions activate the alternative complement pathway cascade with reduction in the serum C3 concentration.

By light microscopy, findings in APSGN include glomerular enlargement, mesangial cell expansion and proliferation, and neutrophil exudation (see Figure 62-2). Electron microscopy (EM) reveals discrete subepithelial deposits.

IgA Nephropathy

IgA Nephropathy (IgAN) is an immune complex–mediated GN. Its course is highly variable and can range from asymptomatic microhematuria to recurrent episodes of gross hematuria to hypertension and acute and chronic renal failure. In Japan, of the children found by mass screening to have IgAN, 70% had asymptomatic microscopic hematuria. In these cases, IgAN is clinically silent. However, in up to 20% of patients who are referred to a pediatric nephrologist, IgAN will progress over decades to chronic renal failure.

The etiology of this disease is unknown. Although many children with IgAN present 1 to 2 days after the beginning of an upper respiratory infection, no infectious etiology has ever been identified. Most IgAN is sporadic, although an autosomal dominant form with incomplete penetrance has been found. Abnormally glycosylated IgA1 is found in the circulation and deposits in the skin and mesangium of the kidneys. The deposition of IgA in the mesangium causes activation of cytokines and growth factors, leading to mesangial expansion and extracellular matrix deposition.

Light microscopic findings show cellular and matrix expansion of the mesangium with deposition of IgA by immunofluorescence. Electron microscopy reveals electron dense deposits within the mesangium that may extend along capillary loops.

Henoch-Schönlein Purpura Nephritis

HSP nephritis is a small vessel vasculitis caused by IgA deposition within the glomeruli in the context of systemic HSP. Renal manifestations may present weeks after the onset of systemic HSP; rarely is it the first feature manifested in this syndrome. Prevalence of renal manifestations is subject to observer bias. Pediatric nephrology centers report that 50% of children with HSPN have hematuria and proteinuria, 8% have acute GN (AGN), 13% have nephrotic syndrome, and 29% have a mixed nephritic and nephrotic syndrome. Treatment of HSP nephritis is controversial because of a high rate of spontaneous remission and the lack of rigorous studies regarding treatment. Prognostic features are noted in Table 62-1.

Table 62-1 Poor Prognostic Features of Selected Glomerulonephritides and Recommended Treatment