Koplik spots pathognomonic

1 to 3 mm whitish, grayish, or bluish elevations with an erythematous base, typically seen on the buccal mucosa opposite the molar teeth, though they can spread to cover the buccal and labial mucosa as well as the hard and soft palate. They have been described as "grains of salt on a red background" . Koplik spots may coalesce and generally last 12 to 72 hours. Koplik spots often begin to slough when the exanthem appears.