Paediatrics

Childhood Exanthems

A febrile child with a widespread rash needs pattern recognition, a rapid safety screen, infection-control action and targeted public-health management rather than rash-description alone.

In a nutshell

Approach a febrile rash by severity first, then by pattern. Measles has the three Cs, Koplik spots and a cephalocaudal rash; rubella is milder with posterior nodes and pregnancy risk; chickenpox has itchy crops; scarlet fever has a sandpaper rash after sore throat. Isolation, notification and protection of vulnerable contacts are core management.

Classic presentation

A febrile child with a generalised rash, where the time course, morphology, distribution, mucosal signs, lymphadenopathy, vaccination and exposure history identify the likely exanthem.

Key points

First ask: is the child toxic, dehydrated, hypoxic, encephalopathic or septic?
A non-blanching rash with systemic illness is an emergency until proven otherwise.
Measles: cough, coryza, conjunctivitis, Koplik spots, then a rash from face/behind ears downwards.
Rubella: fine rash, posterior auricular/suboccipital nodes and major fetal risk in early pregnancy.
Chickenpox: itchy vesicles and crusts in crops at different stages.
Scarlet fever: sore throat, sandpaper texture, strawberry tongue and circumoral pallor.
In England, suspected measles, rubella, chickenpox and scarlet fever require current UKHSA notification.
Do not wait for laboratory confirmation before isolating or contacting public health when measles is suspected.

First-line investigation

Structured clinical assessment with rash morphology, blanching, hydration, respiratory and neurological examination; add disease-specific sampling and public-health testing when indicated.

Management

Assess severity before pattern recognition

Treat non-blanching rash with systemic illness, shock, meningism, respiratory compromise, dehydration, encephalitis or invasive bacterial disease as an emergency.^5,6

Describe the rash and identify the likely exanthem

Use prodrome, morphology, distribution, mucosal signs, lymph nodes, exposure, vaccination and host risk to distinguish measles, rubella, chickenpox and scarlet fever.^1,2,3,4

Isolate and notify

Use separate triage and disease-specific exclusion; notify suspected notifiable disease through the current UKHSA process without waiting for laboratory confirmation.^7,1,2,3,13

Give targeted treatment and protect contacts

Use specialist PEP for vulnerable measles or varicella contacts, refer pregnancy exposures promptly, and treat scarlet fever with current antibiotic guidance.^5,1,9,6,14

Close the prevention and safety-netting loop

Check MMR/MMRV status, explain the return-to-school rule, give red-flag advice and arrange follow-up for complications or persistent diagnostic uncertainty.^{12,15,10,2,13}

Exam traps

Do not diagnose severity from the rash alone.
Measles isolation should not wait for PCR; it is a clinical and public-health diagnosis.
Rubella is often mild in the patient but dangerous to a non-immune pregnancy.
Chickenpox exclusion lasts until lesions crust; scarlet-fever exclusion lasts at least 24 hours after the first antibiotic dose; measles exclusion lasts at least 4 days after rash onset; rubella exclusion lasts at least 5 days after rash onset.
Vitamin A is not a routine outpatient measles prescription; hospitalised high-risk children need specialist discussion.

Illustrations

Erythema infectiosum rash on the handsClinical photograph showing a symmetrical erythematous eruption over the hands and distal forearms in fifth disease (erythema infectiosum).CDC, Wikimedia Commons · Public domain

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.