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Pediatric Rashes – Part 1: Diagnosing Pediatric Exanthem Diseases


Pediatric rashes: How to correctly diagnose
pediatric exanthem diseases? A 4-year-old boy presents to your office with
fever and a prominent rash on his upper body. The young boy appears to be quite ill. His
parents report that the rash appeared yesterday. Six classical pediatric exanthems immediately
come to mind: measles, scarlet fever, rubella – also termed German measles, erythema infectiosum
or “fifth disease”, roseola infantum, and varicella, also known as chickenpox. How
do we correctly characterize the patient’s rash on close examination? The characteristic
distribution and morphology allows for differentiation: In measles, there is an erythematous, partially
confluent exanthem of a dark red color, which usually begins behind the ears and disseminates
to the rest of the body. In addition, there is also a pathognomonic enanthem of the palate
as well as Koplik’s spots, which are clusters of white lesions in the mouth of the patient.
Conjunctivitis is also observed in the majority of patients.  
In scarlet fever, there is a fine, light red and maculopapular rash that develops into
a scarlet-like, partially confluent rash after 1 to 2 days. The rash initially begins on
the neck and spreads to the rest of the body. It is usually most pronounced in the underarm
and groin areas. Non-blanching petechiae (or “Pastia’s lines”) may also be present.
The patient’s face is usually red with perioral pallor. Another classical symptom is a bright
red tongue color with enlarged papillae, also termed strawberry tongue.
If the patient’s rash presents as non-confluent, pink, and maculopapular, then it is most likely
rubella. Like measles, the rash begins primarily behind the ears and extends to the rest of
the body. Patients with erythema infectiosum or fifth
disease do not necessarily develop a rash. Red papules may emerge on the extremities
and trunk that eventually adopt a lace-like reticular appearance. In addition, a blotchy
red rash may appear on the cheeks, which group together within a few hours to form red, slightly
swollen, warm plaques with nasal and perioral sparing. Because of this redness on the cheeks,
erythema infectiosum is also termed “slapped cheek syndrome”.
If the patient’s rash is patchy, rose-pink and usually most pronounced on the torso,
then it is characteristic of roseola infantum, which is also called exanthem subitum or three-day
fever. Before the exanthem phase, patient’s experience a febrile phase with three days
of high fever, followed by a sudden decrease in temperature.
Finally the rash could also be “chickenpox”. The rash observed in chickenpox is widespread,
affecting the entire body including the scalp and oral mucosa. It begins with the appearance
of small red bumps that develop into fluid-filled blisters and pustules that finally form scabs.
Because the rash simultaneously occurs in different stages, the term “starry sky”
is sometimes used to describe this characteristic clinical finding.
Now back to the young boy mentioned at the beginning: his diagnosis is chickenpox, which
is evident from the different stages of blister formation that form a starry sky appearance.

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