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Difficulty: MediumPediatric Infectious Diseases

Match the following atypical and classic clinical descriptions of pediatric viral exanthems with their most likely causative pathogen.

  • After maintaining a temperature of 39.8∘C39.8^\circ\text{C} for several days, a toddler suddenly defervesces. Coinciding exactly with the drop in temperature, a prominent blanching maculopapular eruption emerges primarily across the chest and abdomen.Human herpesvirus 6 (HHV-6)
  • Parents note their preschooler developed noticeably flushed, intensely red cheeks following a mild upper respiratory illness. A fading, net-like erythematous rash is now visible across the proximal extremities.Parvovirus B19
  • A kindergarten student without a vaccination history develops significant photophobia, severe coryza, and a harsh cough. A confluent erythematous rash is observed starting strictly at the top of the forehead and migrating distally over several days.Measles virus (Paramyxovirus)
  • During an evaluation for a mild fever, a child is noted to have distinctly enlarged, tender suboccipital nodes along with a faint pink maculopapular exanthem that appeared on the face yesterday and has already covered the entire body today.Rubella virus (Togavirus)

Answer

The correct matches are: the post-fever truncal rash is caused by HHV-6; the flushed cheeks and reticular rash by Parvovirus B19; the severe prodrome with slowly descending rash by Measles virus; and the rapidly spreading rash with suboccipital adenopathy by Rubella virus.
Each classic viral exanthem possesses distinct clinical signatures: HHV-6 causes rash only after the high fever resolves. Parvovirus B19 causes a distinct facial erythema followed by a reticular rash. Measles virus induces a severe prodrome with a slow, downward-spreading exanthem. Rubella virus causes a rapidly spreading exanthem with prominent tender lymphadenopathy.

Step-by-Step Solution

1
Analyze the relationship between the fever timeline and the rash onset in each clinical description.
The first description notes a rash appearing precisely when the fever breaks, a classic hallmark of roseola infantum.
Differentiating roseola from other viral exanthems relies heavily on its unique temporal sequence (fever first, then rash upon defervescence).
2
Identify distinctive morphological features of the exanthems.
The second description's 'intensely red cheeks' and 'net-like' (reticular) extremity rash strongly identify erythema infectiosum.
Parvovirus B19 has a highly specific dermatologic presentation that distinguishes it from generalized maculopapular rashes.
3
Compare the prodrome severity and rash progression speed of the remaining two maculopapular exanthems.
The third description has a severe prodrome (coryza, cough, conjunctivitis) and slower spread, indicative of measles. The fourth has mild symptoms, prominent occipital adenopathy, and rapid 24-hour spread, indicative of rubella.
Both measles and rubella spread cephalocaudally, but measles takes days to spread and has a severe prodrome, while rubella spreads rapidly and is characterized by marked lymphadenopathy.

Key Concept

Clinical differentiation of classic pediatric viral exanthems based on prodrome severity, rash morphology, and temporal pattern of spread.

Alternative Method

A useful heuristic for pediatric exanthems is to focus on the 'defining outlier' symptom: severe cough/coryza = Measles; prominent occipital nodes = Rubella; rash appearing only after fever stops = Roseola; slapped cheeks = Fifth disease.
Estimated Time:1m 30s
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Pediatric Infectious Diseases

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