see also:

• viruses
• urticaria
• acute rashes in adults

• “exanthems” are acute onset rashes with the term usually applied to children with fevers and macular or maculopapular rashes
• the cause may be viral, bacterial, toxigenic or due to a drug sensitivity
• in the 19th century, childhood exanthems were classified as:
  • measles
  • scarlet fever
  • rubella
  • “fourth disease” - perhaps misdiagnosis of other exanthems
  • fifth disease - erythema infectiosum
  • sixth disease - roseola infantum
• although many will be “non-specific” viral exanthems and self-limiting, it is important to diagnose the specific ones where possible for various reasons:
  • strict isolation and contact tracing: eg. measles
  • isolation from school, kindergartens: eg. measles, rubella, chickenpox, fifth disease, etc
  • pregnant mother issues: eg. rubella, parvovirus, chickenpox, zoster
  • need for penicillins: eg. scarlet fever
  • need to avoid amoxycillin/ampicillin: eg. EBV
  • need to exclude serious conditions: eg. meningococcal septicaemia, Kawasaki's, toxic shock syndrome, Steven's Johnson syndrome, Staph Scalded Skin syndrome
  • concern of serious bacterial infection causing high fevers and unnecessary LPs: eg. roseola
  • differentiating from true drug reactions

• 80% occur in children under 5yrs
• high swinging fever (beyond 39C) for at least 5 days with 4 or 5 of the 5 cardinal features:
  • measles-like rash
  • redness within the mouth or on the pharynx, strawberry tongue, and red or cracked lips
  • red eyes
  • firm swelling of the hands and feet, sometimes including the fingers and toes, with redness of the palms and soles
  • lymphadenopathy with at least one gland > 1.5cm long
• require specific Rx with immunoglobulin, low dose aspirin and follow up Ix as risk of coronary artery aneurysms

• a number of viruses can cause an exanthem associated with an upper respiratory or gastrointestinal infection
• nonpolio enteroviruses in the summer months, and rhinovirus, adenovirus, parainfluenza virus, respiratory syncytial virus and influenza virus in the winter
• Mycoplasma pneumoniae - short-lasting red patches appear on trunk and limbs

• caused by Coxsackie A16 virus and related viruses
• in addition to maculopapular rash, particularly on buttocks, it is characterised by also having mouth ulcers and characteristic purplish vesicles on hands and feet
• in mid-2022, a new paediatric viral examthem thought to be a HFM variant appeared in India nicknamed “tomato flu” as the red lesions can get as big as a tomato, and although self-limiting, causes widespread m/p which can blister including on the palms, and often associated with severe arthralgia, fatigue, nausea, vomiting, diarrhoea, dehydration and bodyaches

• 5-10% children with EBV / glandular fever / infectious mononucleosis develop a rash

• most people with EBV / glandular fever / infectious mononucleosis who start amoxycillin or ampicillin develop a rash within 5-9 days of starting the antibiotic
• the rash is a a characteristic bright-red morbilliform eruption
• starts on the trunk before becoming generalized as confluent macules and papules
• it is NOT a true drug allergy as these can be prescribed to the patient later in life without HS reaction

• usually caused by parvovirus B19
• young adults mainly
• symmetric, painful erythema, and edema of the hands and feet that later progresses to a petechial rash
• oedema and erythema can be observed on the buccal and genital mucosa, and on the inner aspect of the thighs

• aka asymmetric periflexuralexanthem of childhood (APEC)
• ?viral aetiology
• mainly 1-5yr olds
• 60-70% have prodrome of rhinitis, pharyngitis, bronchitis, conjunctivitis, gastroenteritis
• 40-65% have fever
• macular rash starts in one axilla and extends down side of trunk and arm
• lasts weeks

• a characteristic response of the skin to viral infection in which there is a papular rash which lasts for several weeks.
• AKA papulovesicular acrodermatitis of childhood, papular acrodermatitis of childhood and acrodermatitis papulosa infantum

• hepatitis B virus
• EBV / glandular fever / infectious mononucleosis
• Enterovirus infections
• Echo viruses
• Respiratory syncytial virus

• a profuse papular eruption of dull red spots develops over 3-4 days, first on the thighs and buttocks, then on the outer aspects of the arms, and finally on the face.
• 5-10 mm in diameter and are a deep red colour
• may become purple, especially on legs
• may develop into blisters
• may be itchy
• rash lasts 2-8 weeks with mild scaling
• lymphadenopathy may persist for weeks or months
• DermNetNZ pics

• classical raised, red, target-like lesions especially limbs then trunk
• maybe associated with oral and genital lesions
• may be due to various drugs or infections such as:
  • Mycoplasma pneumoniae