Henoch-Schönlein Purpura

Henoch-Schönlein Purpura, the most common vasculitis in children, typically presents with palpable purpura, arthritis, abdominal pain, and kidney involvement, with characteristic ultrasound findings of intestinal wall thickening.

Description

Henoch-Schönlein Purpura (HSP) is an immune-mediated, non-granulomatous small vessel vasculitis, typically affecting the skin, joints, gastrointestinal tract, and kidneys. It is the most common vasculitis in children and is characterised by immunoglobulin A (IgA1) dominant immune deposition in vessel walls and renal mesangium. It is generally a self-limited condition, with a mean duration of 3 – 4 weeks, but can recur in as many as one third of children.

Pathogenesis

HSP is believed to result from an abnormal immune response following an environmental trigger (e.g., upper respiratory tract infection) in a genetically susceptible individual. This leads to IgA1 deposition in small vessel walls, causing vasculitis and organ inflammation.

Subtypes

HSP is typically a single, self-limiting disease without distinct subtypes. However, disease severity can vary, and HSP nephritis is recognised as a serious complication.

Epidemiology, Risk Factors & Associations

• Most common in children aged 3-10 years, but can occur at any age.
• Frequently follows a recent upper respiratory tract infection e.g. β-haemolytic Streptococcus
• Male children are slightly more likely to be affected than female children.
• Seasonal incidence peaks in autumn and winter.

Clinical Features

The tetrad of HSP consists of:

• Palpable nonthrombocytopaenic purpura (predominantly in dependent and pressure-bearing regions, i.e. lower limbs and buttocks)
• Arthritis or arthralgia
• Abdominal pain and vomiting (usually follows within week of rash onset but can precede skin manifestations)
• Renal disease (often asymptomatic initially, but may progress to haematuria or proteinuria) – may be nephritic or nephrotic syndrome.

Complications

• The risk of progression to chronic kidney disease in HSP nephritis varies widely, ranging from 1-20%.
• Sclerosisng ureteritis (very rare) resulting in obstructive uropathy and renal function impairment despite surgical intervention
• Severe gastrointestinal complications can occur but are rare:
  • Intussusception (usually ileoileal)
  • Gastrointestinal haemorrhage
  • Bowel perforation

Pathological Features

Histopathology

• Macroscopic: The skin shows palpable purpura.
• Microscopic: Characteristic leukocytoclastic vasculitis with IgA1-dominant immune deposits in vessel walls. Bowel wall oedema, with submucosal and intramural haemorrhage (usually small bowel).

Serology

• IgA level can be elevated, particularly during acute disease.

Biochemistry

• Non-specific: May show signs of inflammation (e.g., elevated ESR, CRP).
• Haematuria and proteinuria

Radiological Features

General Features

• Characteristically demonstrates gastrointestinal wall thickening and joint effusions.
• Kidney imaging can appear normal or show signs of nephritis.

US

• B-mode¹:
  • Gastrointestinal:
    • Hypoperistalsis, bowel dilatation, bowel wall thickening (uniform or eccentric) secondary to intramural oedema or haemorrhage, peritoneal fluid
    • Intussusception
  • Genitourinary:
    • May appear normal or show signs of nephritis (bilaterally enlarged, echogenic renal cortices).
    • Intramural haematoma may be seen in bladder wall and ureter (uncommon)
    • Scrotal wall thickening, hydrocoele, inflammation of the epididymis and spermatic cord, with or without associated orchitis
• Colour Doppler: No specific features.

Diagnosis

The diagnosis is primarily clinical, based on the presence of the characteristic tetrad (palpable purpura is essential). Skin biopsy can confirm leukocytoclastic vasculitis with IgA deposits, and renal biopsy can confirm HSP nephritis. Imaging helps evaluate for end-organ damage (e.g. of the gastrointestinal and genitourinary systems).

Differential Diagnosis

• Acute rheumatic fever: Arthritis and rash can mimic HSP, but carditis, the response to aspirin, and a history of streptococcal infection can help differentiate.
• Septic arthritis or osteomyelitis: Can mimic the joint involvement of HSP.
• Other causes of vasculitis or purpura (e.g., IgA vasculitis).

Prognosis

Overall excellent prognosis however recurrent haematuria can persist for years.

Management

Management involves supportive care, symptom control, and monitoring for complications. Steroids can be used for severe cases or for specific complications (e.g., severe abdominal pain). Patients with kidney involvement should be referred to a nephrologist for further monitoring and management.

References

1. Khanna, G., Sargar, K. and Baszis, K.W., 2015. Pediatric vasculitis: recognizing multisystemic manifestations at body imaging. Radiographics, 35(3), pp.849-865. ↩︎