**Question:** True about Henoch Schonlein purpura is -

A. It is a vasculitis affecting small blood vessels
B. It primarily affects the skin, joints, kidneys, and gastrointestinal tract
C. It is more common in adults than children
D. It is caused by an infection

**Answer Explanation:**

**Core Concept:** Henoch Schönlein Purpura (HSP) is a small-vessel vasculitis that primarily affects children, characterized by palpable purpura, abdominal pain, arthritis, and renal involvement.

**Why the Correct Answer is Right:**

HSP is a vasculitis, which is an inflammation of small blood vessels. In this case, it affects small blood vessels (capillaries, small arteries, and venules). The condition primarily affects children and is characterized by the following clinical features:

1. Purpura: A palpable, non-itchy, and non-blanching rash, typically affecting the lower extremities.
2. Abdominal pain: Common feature, often relieved by defecation.
3. Joint involvement: Arthralgia and arthritis, usually affecting the knees and ankles.
4. Renal involvement: Proteinuria, hematuria, and hypertension are common.

**Why Each Wrong Option is Incorrect:**

A. While the condition affects small blood vessels, the statement "It is a vasculitis affecting small blood vessels" is too broad and does not address the specific points mentioned in the correct answer.
B. Although HSP can affect the gastrointestinal tract, joints, and kidneys, the statement "It primarily affects the skin, joints, kidneys, and gastrointestinal tract" is too specific and does not cover the overall clinical picture of HSP.
C. HSP is more common in children than adults, making the statement "It is more common in adults than children" incorrect.
D. Infection is not a cause of HSP, which is a post-infectious vasculitis. HSP is triggered by an infection, usually caused by Streptococcus pyogenes, and is characterized by immune complex deposition in small blood vessels.

**Clinical Pearl:** Henoch Schönlein Purpura is a clinical entity that should be considered in the differential diagnosis of children presenting with arthralgia, abdominal pain, and a non-itchy, non-blanching rash. Renal involvement, including hematuria and proteinuria, is common in HSP and should raise suspicion for this condition. Prompt diagnosis and treatment are essential to prevent complications like renal scarring and hypertension.