Most common vasculitis in children:
**Core Concept**
Henoch-Schönlein purpura (HSP) is a form of vasculitis that primarily affects children, characterized by the deposition of IgA immune complexes in small blood vessels, leading to inflammation and damage.
**Why the Correct Answer is Right**
HSP is the most common vasculitis in children, typically presenting with a tetrad of symptoms: non-thrombocytopenic purpura, abdominal pain, arthritis, and renal involvement. The pathophysiology involves the deposition of IgA immune complexes in the walls of small blood vessels, leading to inflammation and damage. This process is thought to be triggered by an immune response to an infectious agent.
**Why Each Wrong Option is Incorrect**
* **Option A:** Kawasaki disease is a medium vessel vasculitis that primarily affects children, but it is less common than HSP and typically presents with fever, rash, and lymphadenopathy.
* **Option B:** Polyarteritis nodosa (PAN) is a medium to large vessel vasculitis that can occur at any age, but it is more common in adults and typically presents with hypertension, kidney disease, and gastrointestinal symptoms.
* **Option C:** Granulomatosis with polyangiitis (GPA) is a small vessel vasculitis that primarily affects adults and typically presents with respiratory symptoms, such as sinusitis and pulmonary nodules.
**Clinical Pearl / High-Yield Fact**
HSP is often triggered by a preceding infection, such as a respiratory or gastrointestinal illness, and may be associated with the presence of IgA nephropathy in some cases.
**Correct Answer:** B. Polyarteritis nodosa