A child has a 2-week history of spiking fevers, which have been as high as 40degC (104degF). She has spindle-shaped swelling of finger joints and complains of upper sternal pain. When she has fever, the parents note a faint salmon-colored rash that resolves with the resolution of the fever. She has had no conjunctivitis or mucositis, but her heart sounds are muffled and she has increased pulsus paradoxus. Which of the following is the most likely diagnosis?

**Core Concept**
The child's presentation is suggestive of a systemic inflammatory disorder characterized by fever, joint inflammation, and a distinctive rash, which resolves with the resolution of fever.

**Why the Correct Answer is Right**
The child's symptoms, particularly the salmon-colored rash that appears with fever and resolves with its resolution, are classic for **Kawasaki disease**. This condition is a medium-vessel vasculitis that predominantly affects children, with an increased risk of coronary artery aneurysms. The presence of increased pulsus paradoxus and muffled heart sounds may indicate cardiac involvement. The absence of conjunctivitis or mucositis helps to differentiate Kawasaki disease from other systemic vasculitides, such as Henoch-Schönlein purpura.

**Why Each Wrong Option is Incorrect**
**Option A:** While rheumatic fever can present with fever and joint inflammation, it typically involves the larger joints and is often accompanied by symptoms such as conjunctivitis and carditis, which are not present in this case.

**Option B:** Juvenile idiopathic arthritis (JIA) can present with joint inflammation and fever, but it does not typically involve a salmon-colored rash that resolves with fever.

**Option C:** Toxic shock syndrome can present with fever, rash, and cardiac involvement, but it is usually accompanied by symptoms such as mucositis and conjunctivitis, which are not present in this case.

**Option D:** Henoch-Schönlein purpura can present with a purpuric rash, but it typically involves the lower limbs and is often accompanied by gastrointestinal symptoms, which are not present in this case.

**Clinical Pearl / High-Yield Fact**
Kawasaki disease is a medical emergency that requires prompt recognition and treatment to prevent long-term cardiac complications. The presence of a salmon-colored rash that resolves with fever is a key diagnostic clue, and treatment should be initiated promptly in suspected cases.

**Correct Answer:** C.

✓ Correct Answer: B. Juvenile idiopathic arthritis