Henoch-Schöenlein Purpura (HSP) is a disease which occurs in childhood; greater than 80% of the patients affected are children between the ages of 5 and 15. HSP can have multiorgan involvement upon presentation. The classic constellation of symptoms and findings includes cutaneous purpura and edema, migratory arthralgias, and spasmodic gastrointestinal pain which can progress to hematochezia, hematemesis, and which may mimic surgical emergencies such as bowel infarction or intussusception; most important in terms of prognosis are the renal manifestations of the disease, which include gross or microscopic hematuria, mild to nephrotic range proteinuria, and possible later progression to chronic renal failure in up to 25% of cases. HSP accounts for up to 3% of terminal renal failure in Europe, but progression to this stage of disease is usually slow, requiring 5 to 10 years for the patient to develop chronic renal insufficiency after a long period of persistent microhematuria and microproteinuria. However, over 50% of affected individuals enjoy complete clinical remission with return of normal renal function indices after an average of 2 years.
Grossly, affected kidneys usually appear normal. Microscopically, HSP affecting the kidney is characterized primarily by glomerular disease, with mesangial and focal and segmental endocapillary proliferation, similar to that seen in classical IgA nephropathy. However, in contrast to this entity, extracapillary proliferation is more commonly seen in HSP nephritis. The phenomenon of mesangial cell "interposition" between the GBM and the endothelial cells, demonstrated on electron microscopy, is a common finding in HSP, and can simulate similar findings in membranoproliferative glomerulonephritis type I. Segmental fibrinoid necrosis can be seen in biopsies of early lesions, and formation of glomerular crescents can be seen in the later stages of more severe disease. These crescents can later contribute to glomerulosclerosis and incite renal failure in some patients.
Immunofluorescence is an important adjunct in the diagnosis of HSP. Examination commonly reveals diffuse mesangial and occasional focal glomerular capillary staining with IgA. Concomitant staining with C3 component of complement is noted in 75-85% of cases, as opposed to IgA nephropathy, in which up to 95% stain for C3.
Electron microscopic examination of these cases reveals mesangial matrix expansion, with electron dense, often "scalloped" or "fluffy" deposits commonly seen in the mesangium. Patients with endocapillary proliferation can show interposition of mesangial cells between the layers of the basement membrane and the endothelial cells of the glomerular tuft.
Contributed by Kevin D. Horn, MD. and Paul S. Dickman, MD.