Pathology and Pathologic Diagnosis

Focal and segmental mesangial proliferation and increased mesangial matrix are seen in the glomerulus (Fig. 504-1). Renal histology demonstrates mesangial proliferation that may be associated with epithelial cell crescent formation and sclerosis. IgA deposits in the mesangium are often accompanied by C3 complement (Fig. 504-2).

Figure 504-1 Light microscopy of immunoglobulin A nephropathy demonstrating segmental mesangial proliferation and increased matrix (×180).

Figure 504-2 Immunofluorescence microscopy of the biopsy specimen from a child with episodes of gross hematuria demonstrating mesangial deposition of immunoglobulin A (×150).

IgA nephropathy is an immune complex disease that appears to be caused by abnormalities in the IgA immune system. The abnormalities identified in the IgA immunoglobulin system have also been observed in patients with Henoch-Schönlein purpura and lends support to the hypothesis that these two diseases are part of the same disease spectrum. Familial clustering of IgA nephropathy cases suggests the importance of genetic factors. Genome-wide linkage analysis suggests the linkage of IgA nephropathy to 6q22-23 in multiplex IgA nephropathy kindreds.

Clinical and Laboratory Manifestations

IgA nephropathy is seen more often in male than in female patients. Though there are rare cases of rapidly progressive forms of the disease, the clinical presentation of childhood IgA nephropathy is often benign in comparison to that of adults. IgA nephropathy is an uncommon cause of end-stage renal failure during childhood. A majority of children with IgA nephropathy in the USA and Europe present with gross hematuria, whereas microscopic hematuria and/or proteinuria is a more common presentation in Japan. Other types of presentation include acute nephritic syndrome, nephrotic syndrome, or a combined nephritic-nephrotic picture. Gross hematuria often occurs within 1-2 days of onset of an upper respiratory or gastrointestinal infection, in contrast to the longer latency period observed in acute postinfectious glomerulonephritis, and may be associated with loin pain. Proteinuria is often <1000 mg/24 hr in patients with asymptomatic microscopic hematuria. Mild to moderate hypertension is most often seen in patients with nephritic or nephrotic syndrome but is rarely severe enough to result in hypertensive emergencies. Normal serum levels of C3 in IgA nephropathy help to distinguish this disorder from poststreptococcal glomerulonephritis. Serum IgA levels have no diagnostic value because they are elevated in only 15% of pediatric patients.

Prognosis and Treatment

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