- Koplik spots are small, bluish-white lesions found on the buccal mucosa and are pathognomonic for measles.
- They appear 1-2 days before the characteristic measles rash and are a crucial early clinical sign.
- These spots help distinguish measles from other viral exanthems like rubella, chickenpox, and scarlet fever, which do not present with Koplik spots.
- Their presence confirms the diagnosis of measles even before the skin rash appears.

Reference: Harrison's Principles of Internal Medicine, 20th Edition, Volume 2, Chapter 250