## Measles Exanthem: Cephalocaudal Progression **Key Point:** The measles rash appears first on the face (especially around the hairline and behind the ears) and spreads downward in a cephalocaudal direction, reaching the trunk by day 2 and the extremities by day 3, with complete spread over 3–4 days. ### Rash Progression Pattern **High-Yield:** The **cephalocaudal (downward) spread** of the measles rash is a classic, frequently tested feature that helps distinguish measles from other viral exanthems. ### Timeline of Exanthem Spread | Day | Location | Characteristics | |-----|----------|------------------| | Day 1 (of rash) | Face, hairline, behind ears | Maculopapular, erythematous, blanching | | Day 2 | Trunk, neck, upper extremities | Rash becomes more confluent | | Day 3–4 | Lower extremities, feet | Rash reaches distal sites; may become confluent on trunk | | Day 5–7 | Fading phase | Rash begins to fade in cephalocaudal order (face first) | ### Clinical Features of the Exanthem - **Morphology:** Maculopapular, initially discrete, becoming confluent on the trunk - **Blanching:** Rash blanches with pressure (non-purpuric) - **Associated findings:** High fever (often 40–40.5°C), persistent cough, conjunctivitis - **Desquamation:** Fine desquamation may follow rash resolution **Clinical Pearl:** The **cephalocaudal progression** is so characteristic that its absence should prompt consideration of alternative diagnoses (e.g., rubella spreads centrifugally; roseola infantum appears as rash after fever subsides). **Mnemonic:** **"Measles = Head-to-Toe"** — starts at the face/head and marches downward to the toes over 3–4 days.
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