Henoch–Schönlein Purpura (HSP), now more properly called IgA vasculitis, is a small-vessel vasculitis that’s almost always IgA-driven. It’s a classic pediatric vasculitis, but can hit adults too.

Core pathophysiology

• Gell and Coomb's Type III (Immune Complex): deposition of IgA immune complexes in small vessels (skin, GI tract, kidneys, joints).
• Histology: leukocytoclastic vasculitis with IgA and C3 deposition on immunofluorescence.
• Triggers: often follows upper respiratory infection (esp. streptococcal, viral).

The classic tetrad of HSP (IgA vasculitis)

1. Palpable purpura – non-thrombocytopenic, mainly on buttocks and legs.
2. Arthralgia/arthritis – knees, ankles commonly affected.
3. Abdominal pain – colicky, may have GI bleeding, intussusception.
4. Renal involvement – hematuria, proteinuria; can present as IgA nephropathy–like GN or even nephritic/nephrotic syndrome.

Labs / findings

• Normal platelets (distinguishes from ITP).
• Serum IgA often elevated.
• Urinalysis: hematuria, proteinuria, RBC casts if nephritis.
• Complement levels (C3/C4) are typically normal (unlike lupus/cryoglobulinemia).

Clinical course

• Kids: often self-limited; symptoms resolve in weeks.
• Adults: higher risk of severe renal disease, sometimes progressing to CKD.