What is the hallmark symptom of pericarditis in children?

The hallmark symptom of pericarditis in children is chest pain that improves with leaning forward. In pericarditis, the inflammation of the pericardium, or the protective sac surrounding the heart, leads to chest discomfort that is often sharp and pleuritic. This pain is typically aggravated by lying flat or with inspiration, contributing to a sense of relief when the patient leans forward.

This positional relief occurs because leaning forward reduces pressure on the pericardium and can alter the position of the heart itself, relieving some of the friction between the inflamed layers.

The other descriptions of chest pain are not characteristic of pericarditis in this context. For example, chest pain that is constant throughout the day does not reflect the typical oscillation experienced in pericarditis. Likewise, radiation of pain to arms is more typical of conditions related to myocardial ischemia or injury, rather than pericarditis. While chest pain that worsens with movement can occur, it is not as definitive a feature as the relief felt when leaning forward.