What clinical sign is characteristic of measles?

Koplick's spots are small, white lesions that appear on the oral mucosa, typically near Stenson's duct, and are a hallmark clinical sign of measles. These spots are often seen in the early stages of measles infection, preceding the characteristic rash by a few days. They are considered pathognomonic for measles due to their distinct appearance and significance in diagnosis.

The presence of Koplick's spots serves as an important indicator to healthcare professionals that a patient could be suffering from measles, especially if accompanied by other symptoms such as high fever and a rash. This early identification is critical, as measles is a highly contagious viral illness, and prompt recognition can help in controlling outbreaks and managing patient care effectively.

In contrast, while conditions like oral thrush might present with white lesions on the tongue or other viral infections may cause painful vesicles in the mouth, these signs are not specific to measles. Similarly, rashes on palms and soles can occur with several other diseases but are not classical for measles. Therefore, the distinct presence of Koplick's spots is key in recognizing measles early in its course.