Examining Exanthems!

What is an exanthem anyway?

  • “A widely spread out rash” – Google
  • “Eruptive disease (such as measles) or its symptomatic eruption” – Merriam-Webster Dictionary
  • History and Etymology: Late Latin exanthema, from Greek exanthēma, from exanthein to bloom, break out, from ex- + anthos flower

Most common exanthems are viral, drug-related, or bacterial, and may be associated with systemic symptoms.

Exanthems tend to be macular, maculopapular, papular, or vesicular / pustular. They differ from enanthems, which occur inside the body (e.g. mucous membranes.)

Measles (aka rubeola)

Source: MSF
Source: UpToDate
  • 3 C’s: cough, coryza, conjunctivitis
  • Fever, malaise
  • Enanthem: Koplik spots
  • Exanthem: maculopapular rash, typically begins 2-4 days after onset of fever
  • Rash classically begins on face and spreads to neck, trunk, extremities
  • Complication: Subacute sclerosing panencephalitis (SSPE), which is caused by persistent infection of the CNS with the virus


Source: CDC
Source: UpToDate
  • Prodrome: fever, headache, sore throat, myalgias
  • Exanthem: maculopapular rash starts on face, then spreads to trunk and extremities, becomes generalized in 24 hrs
  • Similar rash to measles, but spread is much more rapid and rash does not darken or coalesce
  • LAD (posterior cervical, posterior auricular, suboccipital)
  • Arthralgias (teenagers, adult women)


Source: brownskinmatters (Instagram)
Source: UpToDate
  • Prodrome: fever, malaise, pharyngitis, loss of appetite
  • Exanthem: pruritic vesicular rash, begins as macules that rapidly become papules followed by characteristic vesicles
  • Rash appears in successive crops over several days, most lesions crust over within 6 days
  • ~20% children who receive one dose of varicella vaccine may develop varicella infection “breakthrough disease” if exposed (often mild disease, maculopapular)

Erythema infectiosum (aka 5th disease)

Source: Contemporary Pediatrics
Source: UpToDate
  • Cause: Parvovirus B19
  • Prodrome: fever, coryza, headache, nausea, diarrhea
  • Exanthem: classic erythematous malar rash with relative circumoral pallor, followed several days later by a reticulated or lacelike rash on trunk/extremities
  • Rash thought to be immunologically mediated
  • Can cause arthralgias/arthritis (adults), transient aplastic crisis

Roseola (aka 6th disease)

Source: brownskinmatters (Instagram)
Source: UpToDate
  • Cause: HHV-6, may also be caused by HHV-7, enteroviruses, adenovirus, parainfluenza type 1
  • 3-5 days of high fever (may exceed 104°C) that resolves abruptly and is followed by development of a rash
    • Rash begins after viremic phase of illness, coincident with development of antibody to HHV-6, suggesting that it may be result from antigen-antibody complexes
  • Exanthem: erythematous, blanching, macular/maculopapular rash that starts on neck/trunk and spreads to extremities (rash may also be vesicular)
  • Rash typically persists 1-2 days but may come and go within 2-4 hours
  • Associations: Palpebral conjunctivitis, edematous eyelids, seizures, LAD (cervical, postauricular, occipital), encephalitis, thrombotic thrombocytopenic purpura
  • Complications: seizures, aseptic meningitis, encephalitis, TTP


Source: UpToDate
  • Only 5-10% children with EBV manifest an exanthem
  • If amoxicillin or ampicillin is administered, a characteristic bright-red morbilliform eruption almost always occurs
  • Most likely results from ampicillin-antibody immune complexes as a consequence of polyclonal B-cell activation
  • NOT a “true” drug allergy

Atypical exanthems

  • Unilateral laterothoracic exanthem
  • Eruptive pseudoangiomatosis
  • Coxsackie A16 – Hand, foot, mouth syndrome
  • Papular-purpuric gloves and socks syndrome
  • Gianotti-Crosti syndrome

Take-home points!

  • Exanthems = widespread rash
  • Exanthems can be a whole lot of things – viral, drug-induced, bacterial
  • Typical exanthems include measles, rubella, varicella, erythema infectiosum, roseola, EBV
  • Atypical exanthems are in different patterns and include unilateral laterothoracic exanthem, Coxsackie HFM, Papular-purpuric gloves and socks syndrome, and Gianotti-Crosti syndrome
  • History is key to diagnosing exanthems!

Blog post based on Med-Peds Forum talk by Ann Ding, PGY3

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