A patient with clustered white lesions on the buccal mucosa opposite the upper 1st and 2nd molars pathognomonic for measles. These are

Koplik&;s spots: Little spots inside the mouth that are highly characteristic of the early phase of measles (rubeola). The spots look like a tiny grains of white sand, each surrounded by a red ring. They are found especially on the inside of the cheek (the buccal mucosa) opposite the 1st and 2nd upper molars. ref : harrisons 21st ed