A 6-year-old boy from rural Maharashtra presents with a 3-day history of high fever (39.5°C), cough, coryza, and conjunctivitis. On examination, he has a blanching maculopapular rash that started on the forehead and hairline and has now spread to the trunk and limbs. The rash spares the palms and soles. On intraoral examination, you note small white spots with red halos on the buccal mucosa opposite the molars. His mother reports he is unvaccinated. What is the most likely diagnosis?

Explanation

## Diagnosis: Measles ### Clinical Presentation This case presents the classic triad of measles: **Key Point:** The **3 Cs of measles prodrome** — Cough, Coryza, Conjunctivitis — followed by the characteristic **3-day fever** ("3-day measles") before rash onset. ### Pathognomonic Finding: Koplik's Spots **High-Yield:** Koplik's spots are **small white spots with red halos** ("grains of salt on red background") appearing on the buccal mucosa **opposite the molars**, typically 2–3 days before the rash. They are **pathognomonic for measles** and fade as the rash emerges. ### Rash Characteristics | Feature | Measles | Rubella | Varicella | |---------|---------|---------|----------| | **Onset** | Face/hairline → trunk → limbs (cephalocaudal) | Face → trunk (generalized) | Crops on trunk, face, extremities | | **Type** | Blanching maculopapular | Fine maculopapular | Vesicular ("dew drops on rose petals") | | **Palms/Soles** | Spared | Spared | May be involved | | **Prodrome** | 3–4 days (high fever, cough, coryza, conjunctivitis) | Minimal prodrome | 1–2 days (mild fever) | | **Koplik's spots** | Yes (pathognomonic) | No | No | **Clinical Pearl:** Measles rash appears **3–4 days after fever onset** and lasts 5–8 days. The rash is **non-blanching after day 3** as it becomes confluent. ### Vaccination Status The patient is unvaccinated, consistent with measles epidemiology in under-immunized populations. **Mnemonic: MMR** — Measles, Mumps, Rubella vaccine (2 doses; first at 9–12 months, second at 15–18 months in India). ### Complications to Monitor - **Pneumonia** (most common complication) - **Encephalitis** (1 per 1000 cases) - **Otitis media** - **Secondary bacterial superinfection** - **Subacute sclerosing panencephalitis (SSPE)** — rare, 7–10 years post-infection **Key Point:** Vitamin A supplementation (200,000 IU daily × 2 days, then repeat at 2 weeks) is recommended in all measles cases, especially in children <5 years, to reduce morbidity and mortality.