What is HSP (Henoch-Schönlein Purpura)?
HSP is an IgA-mediated systemic small vessel vasculitis that predominantly affects children aged 3-10 years, characterized by a classic tetrad of palpable non-thrombocytopenic purpura, arthralgia/arthritis, abdominal pain, and renal involvement 1, 2.
Pathophysiology
HSP results from IgA1-dominant immune complex deposition in small blood vessel walls, leading to leukocytoclastic vasculitis 3, 2. The exact trigger remains unknown, though the disease is fundamentally an immune-mediated process affecting capillaries, venules, and arterioles throughout multiple organ systems.
Clinical Manifestations
The disease presents with a characteristic pattern, though not all features appear simultaneously:
Cutaneous Features
- Palpable purpura is the hallmark finding - non-blanching, raised purpuric lesions typically starting on lower extremities and buttocks, often spreading to other areas 1, 4
- The rash may be pruritic and painful
Musculoskeletal Involvement
- Joint manifestations occur in 82% of cases - typically affecting knees and ankles with arthralgia or frank arthritis 4
- In 22% of cases, joint symptoms precede the purpuric rash (atypical presentation) 4
Gastrointestinal Involvement
- Abdominal pain affects approximately 54% of patients 4
- Can range from mild colicky pain to severe complications including intussusception, GI bleeding, bowel angina, or perforation 5, 6
- Fecal occult blood positivity is common
Renal Involvement
- Occurs in 19-54% of cases, with most manifestations appearing within the first month after disease onset 7, 4
- Ranges from isolated microscopic hematuria (most common) to severe crescentic glomerulonephritis
- Adults have worse renal prognosis than children 7
Age-Related Differences
Children (majority of cases):
- Generally self-limited disease with favorable long-term outcomes 7
- Lower incidence of severe renal complications
Adults:
- More aggressive course with higher risk of severe renal involvement and progression 7, 3
- Greater likelihood of persistent proteinuria >1 g/day
- Higher morbidity and mortality
Diagnostic Approach
Clinical diagnosis is primarily based on the classic tetrad, but confirmation requires:
- Skin or renal biopsy showing leukocytoclastic vasculitis with IgA deposition increases diagnostic sensitivity and specificity 2
- Renal biopsy is indicated in children with decreased renal function at presentation or severe nephrotic/nephritic syndrome 7
- Laboratory findings: elevated serum IgA levels, hematuria, proteinuria, elevated BUN/creatinine in renal involvement 3
Prognosis
The vast majority of children with HSP have self-limited disease and excellent long-term outcomes 7. However, long-term prognosis is primarily determined by the degree of renal involvement. Recurrences occur in approximately 15% of patients 4. Adults face higher risk of progression to chronic kidney disease, particularly with proteinuria >1 g/day 7.
Key Clinical Pitfalls
- Do not assume HSP is always benign - while self-limited in most children, adults and those with significant renal involvement require aggressive monitoring
- Joint symptoms may precede purpura in 22% of cases, potentially delaying diagnosis 4
- Renal involvement can occur late - up to 68% of renal manifestations appear within the first month, but monitoring should continue for at least 6 months 4
- Cardiac and neurological complications are rare but serious - arrhythmias and neurological involvement require immediate intensification of therapy 5