**Core Concept**
Hypersensitivity vasculitis, also known as leukocytoclastic vasculitis, is a form of small vessel vasculitis characterized by inflammation of blood vessels due to an immune-mediated reaction. This condition is often triggered by infections, medications, or other allergens.

**Why the Correct Answer is Right**
The correct answer is associated with Henoch-Schönlein purpura (HSP), a classic example of hypersensitivity vasculitis. HSP is characterized by the deposition of IgA immune complexes in the walls of small blood vessels, leading to inflammation and damage. This results in symptoms such as palpable purpura, arthritis, abdominal pain, and renal involvement. The IgA immune complex deposition is a hallmark of HSP and is often seen in the skin, kidneys, and other organs.

**Why Each Wrong Option is Incorrect**
* **Option A:** While systemic lupus erythematosus (SLE) is an autoimmune disease that can cause vasculitis, it is not the most common cause of hypersensitivity vasculitis.
* **Option B:** Polyarteritis nodosa (PAN) is a form of medium vessel vasculitis, not small vessel vasculitis like hypersensitivity vasculitis.
* **Option C:** Eosinophilic granulomatosis with polyangiitis (EGPA) is a form of vasculitis that affects the lungs, skin, and other organs, but it is not the most common cause of hypersensitivity vasculitis.

**Clinical Pearl / High-Yield Fact**
Henoch-Schönlein purpura (HSP) is often associated with a characteristic "palpable purpura" on the lower extremities, which is a classic exam finding. Remember the "Buerger's" criteria for diagnosing HSP: palpable purpura, abdominal pain, arthritis, and renal involvement.

**Correct Answer: C. Henoch-Schönlein purpura**