What is Henoch-Schönlein Purpura (HSP)?
Henoch-Schönlein Purpura (HSP), now termed IgA vasculitis, is an IgA-mediated systemic small-vessel vasculitis characterized by the clinical finding of palpable purpura plus at least one of the following: renal involvement (hematuria and/or proteinuria), arthritis/arthralgia, or abdominal pain. 1, 2
Pathophysiology
- HSP is caused by deposition of IgA-dominant immune complexes in small blood vessels, leading to leukocytoclastic vasculitis 3, 4
- The disease involves aberrantly glycosylated IgA1 molecules that form immune complexes, which deposit in the mesangium and subepithelial/subendothelial spaces of glomeruli 5
- These deposited immune complexes trigger mesangial proliferation and renal damage, likely requiring complement system activation 5
Clinical Presentation
The classic tetrad includes: 4, 6
- Palpable purpura (non-thrombocytopenic) - typically on lower extremities and buttocks
- Arthritis or arthralgia - commonly affecting knees and ankles
- Abdominal pain - may include gastrointestinal bleeding
- Renal involvement - hematuria and/or proteinuria
Epidemiology
- HSP is the most common form of systemic vasculitis in children, with an incidence of 10-20 cases per 100,000 children per year 2, 6
- Approximately 90% of cases occur in children aged 2-10 years, with peak incidence at 4-7 years 2
- The disease primarily affects children but can occur in adults, though adult-onset is less common and carries worse prognosis 1, 4
Organ System Involvement
Renal manifestations: 5
- Glomerulonephritis (HSPN) occurs in 30-50% of HSP patients
- Most cases are mild, but a small percentage present with nephrotic syndrome or renal failure
- Renal involvement is the most important prognostic factor determining long-term morbidity and mortality 2
Gastrointestinal manifestations: 2
- Diffuse abdominal pain is common
- Complications can include gastrointestinal bleeding and intussusception
Musculoskeletal manifestations: 3
- Arthritis or arthralgia, typically affecting large joints of lower extremities
Other rare manifestations: 7
- Orchitis, central nervous system involvement, and myocarditis have been reported 6
Diagnostic Approach
Clinical diagnosis is made when palpable purpura is present plus at least one of the following: 1
- Renal involvement (hematuria and/or proteinuria)
- Arthralgia or arthritis
- Abdominal pain
- Biopsy showing predominant IgA deposition 2
Essential laboratory evaluation includes: 1
- Urinalysis with microscopy to assess for proteinuria, red blood cell casts, and dysmorphic red blood cells
- Basic metabolic panel including BUN and serum creatinine to assess renal function
- Complete blood count with platelets to rule out thrombocytopenia
- Blood pressure measurement, as hypertension may indicate severe renal involvement
Biopsy findings: 7
- Immunofluorescence or immunohistochemistry is essential to demonstrate IgA deposition in affected tissues
- IgA nephropathy/Henoch-Schönlein purpura can be overlooked without proper immunofluorescence studies
Natural History and Prognosis
- Most cases are self-limited with an average disease duration of 4 weeks 2
- HSP spontaneously resolves in 94% of children and 89% of adults 6
- Long-term complications are rare but include persistent hypertension and end-stage kidney disease 2
- Renal involvement can persist and relapse years after initial presentation, making 6 months of follow-up prudent 6
- Adults have worse prognosis and higher risk of progression to end-stage renal disease compared to children 1