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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- Measles: cough, coryza, conjunctivitis, Koplik spots (pathognomonic white spots on buccal mucosa), maculopapular rash starting behind ears spreading down. Notifiable. Complications: encephalitis, SSPE
- Chickenpox (VZV): crops of vesicles at different stages (macule-papule-vesicle-pustule-crust), centripetal distribution, intensely itchy. Treat with calamine, NOT aspirin (Reye syndrome). Aciclovir if immunocompromised
- Scarlet fever (Group A Strep): sandpaper-textured rash, strawberry tongue, perioral pallor, Pastia lines. Treat with penicillin V. Notifiable
- Roseola (HHV-6): high fever for 3–5 days then rash appears AS fever settles. Classic trigger of febrile seizures
- Erythema infectiosum/fifth disease (parvovirus B19): slapped cheek rash then lacy reticular rash on limbs. Dangerous in pregnancy (hydrops fetalis) and sickle cell (aplastic crisis)
- Hand-foot-and-mouth (Coxsackie A): vesicles on palms, soles, and oral mucosa. Self-limiting
Overview
Childhood exanthems are rash-producing viral or bacterial infections that are common in paediatric practice. Accurate clinical differentiation is essential for appropriate management, isolation advice, and recognition of complications. Some conditions are notifiable (measles, scarlet fever, rubella) and some have specific implications in pregnancy (rubella — congenital rubella syndrome; parvovirus B19 — hydrops fetalis) or in immunocompromised hosts (varicella — disseminated disease).
Epidemiology
Chickenpox is the most common childhood exanthem, with >90% of children infected before adolescence in the pre-vaccine era. Measles incidence has risen in areas with reduced MMR uptake. Scarlet fever incidence increased significantly in the UK from 2014. Most exanthems are self-limiting in immunocompetent children but can cause serious complications in pregnancy, neonates, and immunocompromised individuals.
Clinical Features
Symptoms
Measles: prodrome of cough, coryza, conjunctivitis (the 3 Cs) and Koplik spots, followed by maculopapular rash starting behind ears
Chickenpox: itchy vesicular rash in crops at different stages, centripetal (trunk > limbs)
Scarlet fever: sore throat, fever, then sandpaper rash starting on neck/trunk, strawberry tongue, circumoral pallor
Roseola: high fever 3–5 days, rash appears as fever resolves, often triggers febrile seizure
Fifth disease: slapped cheek appearance, then lacy reticular rash on limbs, arthralgia in older children/adults
Signs of encephalitis: altered consciousness, seizures, focal neurology (measles, VZV complication)
Signs
Koplik spots (measles): white-grey spots on erythematous buccal mucosa opposite molars — pathognomonic, appear before rash
Pastia lines (scarlet fever): linear petechial streaks in flexural creases (axillae, antecubital fossae)
Vesicles on palms and soles (hand-foot-and-mouth) — unusual distribution
Dermatomal vesicular rash (herpes zoster/shingles — reactivation of VZV)
Investigations
First-line
Clinical diagnosisMost childhood exanthems are diagnosed clinically based on rash morphology, distribution, and associated features
Throat swabIf scarlet fever suspected — rapid antigen test or culture for Group A Streptococcus
Second-line
Measles serologyIgM antibodies or PCR from oral fluid swab — required for notification and public health
Parvovirus B19 IgMIf pregnant contact, sickle cell disease, or immunocompromised
VZV PCRVesicle fluid — for atypical presentations or immunocompromised
Specialist
Notify PHEMeasles, rubella, and scarlet fever are notifiable diseases
Management
NICE CKS and PHE guidelines1
Measles
- Supportive: fluids, paracetamol for fever
- Notifiable disease — inform public health
- Vitamin A supplementation in severe cases or malnourished children
- Complications: otitis media (most common), pneumonia (most common cause of death), encephalitis, SSPE (years later)
- Exclusion from school for 4 days after rash onset
- Prevention: MMR vaccine at 12–13 months and 3 years 4 months
2
Chickenpox
- Supportive: calamine lotion, antihistamines for itch, paracetamol
- Do NOT give aspirin (Reye syndrome) or ibuprofen (theoretical increased risk of necrotising fasciitis with VZV)
- Aciclovir: for immunocompromised, neonates, and severe disease
- Exclude from school until all lesions have crusted (usually 5 days after rash onset)
- VZIG (varicella-zoster immunoglobulin): for high-risk contacts who are non-immune (immunocompromised, neonates, pregnant women)
3
Scarlet fever
- Penicillin V for 10 days (first-line). Clarithromycin if penicillin-allergic
- Notifiable disease
- Complications: peritonsillar abscess, rheumatic fever, post-streptococcal GN, invasive GAS (rare)
4
Other exanthems
- Roseola: supportive only — resolves spontaneously
- Fifth disease: supportive. Avoid contact with pregnant women (risk of hydrops fetalis). Check parvovirus IgG in sickle cell contacts
- Hand-foot-and-mouth: supportive — maintain hydration if oral ulcers painful
Complications
- Measles: Otitis media, pneumonia (most common cause of death), encephalitis (1 in 1,000), SSPE (years later, fatal)
- Chickenpox: Secondary bacterial skin infection (GAS), pneumonia, encephalitis/cerebellitis, purpura fulminans
- Scarlet fever: Rheumatic fever, post-streptococcal GN, invasive GAS disease
- Parvovirus B19: Aplastic crisis in sickle cell disease, hydrops fetalis if maternal infection in pregnancy
UKMLA Exam Tips
- 1Koplik spots = measles (pathognomonic). Appear BEFORE the rash
- 2Roseola: fever THEN rash (rash appears as fever resolves). Most common cause of febrile seizures from an identifiable virus
- 3Chickenpox vesicles appear in CROPS at different stages — centripetal distribution (trunk > limbs)
- 4Scarlet fever: sandpaper rash + strawberry tongue + circumoral pallor + Pastia lines. Treat with penicillin V
- 5Parvovirus B19 and pregnancy: risk of hydrops fetalis. Parvovirus B19 and sickle cell: aplastic crisis
- 6Do NOT give ibuprofen in chickenpox — use paracetamol only
- 7Fifth disease: by the time slapped cheek rash appears, the child is no longer infectious
practicetest your knowledge on Common Childhood ExanthemsApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — Paediatrics and beyond.
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