Key Facts

HSP is the most common childhood vasculitis and is usually a benign, self-limiting condition. The most important complication is renal disease, which requires monitoring for up to 12 months after the acute episode.

Epidemiology

Incidence: approximately 20 per 100,000 children per year. Peak age: 3-10 years. Male:female ratio 1.5:1. More common in autumn/winter. Rare in adults (but when it occurs, renal involvement is more severe).

Aetiology

• Trigger: Preceding URTI in ~50-75% of cases
• Infections: Group A Streptococcus, adenovirus, parvovirus B19, Mycoplasma
• Other triggers: Drugs, insect bites, food allergens
• Pathogenesis: IgA immune complex deposition in small vessel walls

Pathophysiology

HSP is an IgA-mediated small vessel vasculitis (leucocytoclastic vasculitis). IgA1 immune complexes deposit in the walls of small blood vessels (skin, joints, gut, kidneys), causing complement activation, neutrophil infiltration, and vessel wall damage. In the kidneys, IgA deposition in the glomerular mesangium causes a proliferative glomerulonephritis identical to IgA nephropathy.

Classic Tetrad

1. Purpura (100%): Palpable, non-thrombocytopenic purpura on buttocks and lower limbs (extensor surfaces); may also affect arms and trunk
2. Arthralgia/arthritis (75%): Knees and ankles most commonly; periarticular swelling; non-deforming
3. Abdominal pain (65%): Colicky; may be severe; GI bleeding (melaena, haematemesis) in 20-30%
4. Renal (40%): Microscopic haematuria, proteinuria; macroscopic haematuria in ~5%; nephrotic syndrome rarely

Other Features

• Scrotal swelling/pain (~15% of boys — may mimic testicular torsion)
• Subcutaneous oedema (face, hands, feet — especially in young children)
• Rarely: CNS involvement (headache, seizures, altered consciousness)

Red Flags

• Heavy proteinuria (uPCR >200) — risk of nephrotic syndrome/renal impairment
• Hypertension — renal involvement
• Severe abdominal pain with bloody stool — consider intussusception (ileo-ileal, not the ileocolic type seen in typical intussusception)
• Scrotal pain — exclude testicular torsion
• Relapse with worsening renal function — nephrology referral

Bedside

• Urine dipstick: Haematuria, proteinuria — at diagnosis and weekly for 4 weeks, then monthly for 6-12 months
• Blood pressure: Monitor throughout

Bloods

• FBC: Platelets NORMAL (distinguishes from ITP)
• U&Es: Renal function
• CRP/ESR: May be mildly elevated
• IgA: Elevated in ~50% (supports diagnosis but not diagnostic)
• Coagulation: Normal
• ASOT/throat swab: If preceding streptococcal infection suspected

Imaging

• USS abdomen: If severe abdominal pain — exclude intussusception
• Doppler USS testes: If scrotal swelling — exclude torsion

Special Tests

• Urine protein:creatinine ratio (uPCR): Quantify proteinuria if dipstick positive
• Renal biopsy: Only if progressive renal impairment, heavy proteinuria (uPCR >200), or nephrotic syndrome — IgA mesangial deposits
• Skin biopsy: Rarely needed — leucocytoclastic vasculitis with IgA deposits

Non-pharmacological

• Supportive care: Rest, adequate hydration, elevation of affected limbs
• Monitoring: Weekly urine dipstick and BP for 4 weeks; then monthly for 6-12 months

Pharmacological

• Analgesia: Paracetamol 15mg/kg QDS + ibuprofen 10mg/kg TDS (if no renal involvement)
• Prednisolone 1-2mg/kg/day (max 40mg): Consider for severe abdominal pain or scrotal pain; does NOT prevent nephritis
• ACEi (ramipril): If significant proteinuria — reduces proteinuria and slows renal progression

Renal Involvement Management

• Mild (microscopic haematuria/mild proteinuria): Monitor; usually resolves
• Moderate (heavy proteinuria/macroscopic haematuria): Nephrology referral; ACEi
• Severe (nephrotic syndrome/declining renal function): Immunosuppression (cyclophosphamide, mycophenolate) — guided by renal biopsy

Referral Criteria

• Heavy proteinuria (uPCR >200) — paediatric nephrology
• Declining renal function — nephrology urgently
• Hypertension — nephrology
• Severe abdominal pain not responding to steroids — surgical review (intussusception)
• Scrotal swelling — urology if torsion cannot be excluded

• Self-limiting: ~95% resolve within 4-6 weeks
• Relapse: ~30% have at least one relapse (usually milder)
• Renal involvement: ~40% have haematuria/proteinuria; <5% progress to significant renal disease; <1% develop ESRD
• Long-term renal follow-up: Monitor for 12 months; late-onset nephritis can occur weeks to months after initial presentation
• Pregnancy: Women with history of HSP nephritis have increased risk of hypertension and proteinuria in pregnancy

HSP Monitoring Schedule

EULAR/PRINTO/PRES Classification Criteria