Final answer:
The described rash is characteristic of measles, which is known for its maculopapular rash starting on the face and spreading, along with distinctive Koplik's spots in the oral mucosa. Chickenpox, roseola, and syphilis present differently.
Step-by-step explanation:
The maculopapular rash described, with a red base and a small white papule in the center, is indicative of measles. Measles, also known as rubeola, typically presents with a raised macular rash that begins on the face and spreads to the extremities. Additionally, Koplik's spots, which are small white spots on the oral mucosa, are characteristic of measles.
The description does not match chickenpox, which is characterized by a pustular rash concentrated mainly on the trunk and is caused by the varicella-zoster virus. Roseola generally begins with a high fever and a pink, patchy rash that starts on the trunk and spreads outward, often following the fever's resolution. The rash in roseola does not start with a red base and a central white papule. Finally, syphilis, caused by the bacterium Treponema pallidum, can also result in a rash but it manifests differently, with a non-itchy rash that can appear on the palms of the hands and soles of the feet.
The final answer in two line explanation in 300 words: The correct diagnosis for a rash with a red base and small white papules in the center, characteristic of measles, is b) Measles.