Okay, let's tackle this question about Kawasaki's disease. The user wants a detailed explanation for the MCQ. First, I need to recall the key points about Kawasaki's disease.

The question asks which statement is false. Let's look at each option.

Option A says it's the most common immune-mediated vasculitis in children. From what I remember, Kawasaki's is indeed the leading cause of acquired heart disease in developed countries, so A is true.

Option B mentions coronary artery aneurysms in 25% of patients. I think the incidence is around 15-20%, so 25% is a bit high but close enough. Maybe the exact percentage is a trap here. Wait, some studies say up to 25% if untreated. But with treatment, it's lower. So B might be correct.

Option C states IVIG is indicated only in patients with coronary artery aneurysms. That seems wrong. IVIG is the standard treatment to prevent aneurysms, given early in the course. So C is the incorrect statement.

Option D refers to skin, mucus membranes, and lymph nodes being involved. Classic signs include conjunctival injection, rash, oral changes, and lymphadenopathy. So D is correct.

So the incorrect answer is C. Now, I need to structure the explanation according to the user's guidelines. Make sure each section is covered with the right details. Check for the clinical pearl, maybe about IVIG timing and dosage. Also, mention that IVIG is given to all diagnosed patients regardless of aneurysms.

**Core Concept**
Kawasaki's disease is an acute systemic vasculitis primarily affecting children, characterized by inflammation of medium-sized arteries, particularly the coronary arteries. Early treatment with intravenous immunoglobulin (IVIG) and aspirin is critical to reduce coronary artery aneurysm risk.

**Why the Correct Answer is Right**
**Option C** is false because IVIG is indicated **in all patients with diagnosed Kawasaki's disease**, regardless of coronary artery involvement. IVIG is administered early (within 10 days of fever onset) to suppress inflammation and prevent aneurysms. The standard dose (2 g/kg) is given even in asymptomatic cases to mitigate long-term cardiac complications.

**Why Each Wrong Option is Incorrect**
**Option A:** True. Kawasaki's disease is the most common immune-mediated vasculitis in children, with a peak incidence in those under 5 years.
**Option B:** True. Untreated patients develop coronary artery aneurysms in ~25%, but this drops to 5% with timely IVIG and aspirin therapy.
**Option D:** True. Classic clinical features include polymorphic rash, conjunctival injection (mucous membrane involvement), and cervical lymphadenopathy (>1 cm).

**Clinical Pearl / High-Yield Fact**
Never delay IVIG administration in suspected Kawasaki's disease. Early treatment (within 10 days of fever onset) reduces aneurysm risk to <5%. Remember the acronym **CRASH and BURN** to recall key features: **C**onjunctivitis, **R**ash, **A**ndymenorrhea, **S**loughing, **H**ands/feet changes; **B**i-lateral lymphadenopathy, **U**nic

✓ Correct Answer: B. ac