Which viral exanthem presents with Koplik's spots, cough, coryza, conjunctivitis, and a macular rash that begins at the head and progresses downward?

• A. Measles
• B. Scarlet fever
• C. Rubella
• D. Fifth disease

Answer: (A)

Koplik spots are a hallmark of measles and, when seen with the 3 Cs—cough, coryza, and conjunctivitis—the picture points directly to measles rather than other viral exanthems. The rash in measles is maculopapular and classically starts on the face (around the hairline or behind the ears) and then spreads downward to the trunk and limbs—a cephalocaudal progression that unfolds over several days.

Koplik spots appear on the inner cheek mucosa as small white or bluish-white dots with a reddish base and typically appear before the rash, helping to distinguish measles from other infections. In contrast, rubella tends to produce a milder illness with a fine rash that also starts on the face but lacks Koplik spots and the prominent respiratory symptoms. Fifth disease presents with a “slapped-cheek” facial erythema and a later lacy body rash, while scarlet fever features a sandpaper-like rash and fever but not Koplik spots or the same pattern of conjunctivitis and coryza.

Thus, the combination of Koplik spots, the 3 Cs, and a cephalocaudal macular eruption is most consistent with measles.