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- Henoch-Schönlein purpura (HSP), also called immunoglobulin A vasculitis, is an immunologically mediated, purpuric, nonthrombocytopenic, and systemic vasculitis involving the small blood vessels of the skin, gastrointestinal (GI) tract, joints, and kidneys.
- Diagnosis is defined by the presence of at least two of the following classification criteria:
- Palpable purpura (not related to thrombocytopenia)
- Age ≤20 years at onset
- Abdominal pain
- Biopsy showing granulocytic infiltrates in the walls of arterioles or venules
- One of the most common acute vasculitides in childhood
- Occurs most frequently between the ages of 3 and 15 years
- Incidence of 13.5 cases per 100,000 children per year
- Male predominance
- Seasonal variation, with most cases occurring primarily in the winter
Preliminary studies suggest that certain human leukocyte antigen types may be associated with an increased risk of HSP and nephritis. Patients with complement deficiencies and IgA-related disorders may be predisposed to HSP.
- Predominantly an IgA-mediated immune response to antigen and operates through the alternative complement pathway
- There is a characteristic vascular deposition of IgA in affected organs.
- IgA immune deposits affect the small vessels, predominantly capillaries, arterioles, and venules.
- Studies suggest that renal injury in HSP is due to galactose-deficient IgA1 that is recognized by antiglycan antibodies, leading to the formation of circulating immune complexes and their mesangial deposition
- Renal biopsy shows proliferative glomerulonephritis with an increase in endothelial and mesangial cells, ranging from focal and segmental lesions to severe crescentic disease.
- Genetically predisposed hosts may be susceptible to the following associations and triggers.
- Many cases are preceded by an upper respiratory tract infection (URI), particularly β-hemolytic streptococci.
- Other infectious associations include viral infections (varicella, rubella, rubeola, hepatitis A and B), Mycoplasma pneumoniae, Bartonella henselae, and Helicobacter pylori.
- Vaccinations, drug exposure, and insect bites have been implicated as possible triggers.