Pathogenesis and Pathology

The pathogenesis of HSP nephritis appears to be mediated by the deposition of polymeric immunoglobulin A (IgA) in glomeruli. This is analogous to the same type of IgA deposits seen in systemic small vessels, primarily those of the skin and intestine. The glomerular findings can be indistinguishable from those of IgA nephropathy. IgA deposits are present by immunofluorescence, and a broad spectrum of glomerular lesions that can range from mild proliferation to necrotic and crescentic changes can be seen.

Clinical and Laboratory Manifestations

The nephritis that can accompany HSP usually follows onset of the rash, often weeks or even months after the initial presentation of the disease. Nephritis can be manifest at initial presentation but only rarely before onset of the rash. Patients at presentation rarely display a severe combined acute nephritic and nephrotic picture (hematuria, hypertension, renal insufficiency, significant proteinuria, and nephrotic syndrome). Most patients have only mild renal manifestations, principally isolated microscopic hematuria without significant proteinuria. Initial mild renal involvement can progress to more severe nephritis despite resolution of all other features of HSP. The severity of the systemic manifestations does not correlate with the severity of the nephritis. Most patients who develop nephritis have urinary abnormalities by 1 month, and nearly all have abnormalities by 3 months after onset of HSP. Therefore, a urinalysis should be performed weekly in patients with HSP during the period of active clinical disease. Thereafter, a urinalysis should be performed once a month for up to 6 mo. If all urinalyses are normal, then nephritis is unlikely to develop. If proteinuria, renal insufficiency, or hypertension develops along with hematuria, consultation with a pediatric nephrologist is indicated.

Prognosis and Treatment

The prognosis of HSP nephritis for most patients is excellent. Spontaneous and complete resolution of the nephritis typically occurs in those with mild initial manifestations (isolated hematuria with insignificant proteinuria). However, such patients can progress to severe renal involvement, including development of chronic renal failure. Patients with acute nephritic or nephrotic syndrome at presentation have a guarded renal prognosis, especially if they are found to have concomitant necrosis or substantial crescentic changes on renal biopsy. Untreated, the risk of developing chronic kidney disease, including renal failure, is 2-5% in all patients with HSP but almost 50% in those with the most severe clinical and histologic features.

No studies have demonstrated whether short courses of oral corticosteroids administered promptly after onset of HSP have a significant favorable effect on the subsequent development or severity of subsequent HSP nephritis. Tonsillectomy has been proposed as an intervention for HSP nephritis, but it does not appear to have any measurable effect. Mild HSP nephritis does not require treatment because it usually resolves spontaneously.

Limited prospective controlled trials have been performed for severe HSP nephritis, and none have shown benefit from any therapy studied. Several uncontrolled studies have reported benefit from aggressive immunosuppression (high-dose and extended courses of corticosteroids with cyclophosphamide or azathioprine) in patients with poor prognostic features who might be expected to have a high risk of chronic renal failure. Aggressive therapy with careful monitoring may be reasonable in those with the most severe HSP nephritis (>50% crescents on biopsy).