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IgA vasculitis (formerly Henoch–Schönlein purpura, HSP) is a small-vessel vasculitis characterized by IgA1-dominant immune complex deposition, primarily affecting skin, joints, gastrointestinal tract, and kidneys. It is the most common systemic vasculitis in children, though adults can be affected and tend to have more severe disease.

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Epidemiology

Feature	Description
Age	Most common in children aged 3–15 years
Sex	Slight male predominance
Seasonality	Peaks in fall and winter
Trigger	Often follows upper respiratory infection or other antigenic stimulus
(e.g., Group A Streptococcus, vaccines, drugs)

Pathophysiology

Immune complex–mediated vasculitis due to IgA1 deposition in vessel walls
Targets dermal, renal, GI, and synovial small vessels
Leads to leukocytoclastic vasculitis with fibrinoid necrosis of postcapillary venules
Similar mechanism to IgA nephropathy, sometimes overlapping

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Clinical Features

Feature	Description
Palpable purpura	Non-blanching, symmetric, lower extremities and buttocks
Arthritis/arthralgia	Non-deforming, migratory
Abdominal pain	Intermittent, colicky; may have vomiting, GI bleeding
Hematuria/proteinuria	Can progress to IgA nephropathy-like glomerulonephritis
Scrotal swelling	May mimic testicular torsion in males

EULAR/PRINTO/PRES Clinical Criteria:

Mandatory criterion: Palpable purpura (non-thrombocytopenic) Plus ≥1 of the following:

Organ system	Findings
Joints	Arthritis/arthralgia (knees and ankles most common)
GI	Colicky abdominal pain, GI bleeding, intussusception (esp. in young children)
Kidneys	Hematuria, proteinuria, nephritic/nephrotic syndrome
Skin biopsy	Leukocytoclastic vasculitis with IgA deposition

Laboratory Findings

Test	Typical Result
CBC	Normal platelets (excludes thrombocytopenic purpura)
ESR/CRP	Elevated in active inflammation
Urinalysis	Hematuria, proteinuria
Renal function	Monitor for rising creatinine or GFR decline
IgA levels	Elevated in ~50% (non-specific)
Coagulation profile	Normal (rules out DIC or other bleeding disorders)