Childhood exanthems

Feature	Rubella (German Measles)	Measles (Rubeola)	Scarlet Fever	Erythema Infectiosum (Fifth Dis.)	Roseola Infantum (Sixth Dis.)	Varicella (Chickenpox)
Agent	Togavirus (RNA)	Paramyxovirus (RNA)	S. pyogenes (GAS) exotoxin	Parvovirus B19 (DNA)	HHV-6, HHV-7 (DNA)	VZV (HHV-3) (DNA)
Prodrome	Low-grade fever, postauricular/occipital LAD, arthralgias.	3 C’s: Cough, Coryza, Conjunctivitis. High fever.	Fever, pharyngitis, headache, vomiting.	Mild flu-like sx.	High fever (>40°C) for 3-5 days, child appears well.	Fever, malaise.
Enanthem	Forchheimer spots (petechiae on soft palate)	Koplik spots (blue-white spots on buccal mucosa). Pathognomonic.	Strawberry tongue, palatal petechiae.	N/A	Nagayama spots (papules on soft palate).	Ulcers in mouth/pharynx.
Exanthem	Maculopapular rash starts on face, spreads caudally in <24h. Lighter than measles.	Maculopapular rash starts at hairline, spreads caudally. Confluent.	”Sandpaper” texture, diffuse erythema. Starts on trunk, spreads out. Spares palms/soles. Circumoral pallor.	”Slapped cheeks” (malar rash), followed by lacy, reticular rash on trunk/extremities.	Maculopapular rash appears as fever breaks. Starts on trunk, spreads to face/extremities.	Vesicular rash on erythematous base (“dew drop on a rose petal”). Lesions in different stages. Starts on trunk, spreads to face/limbs.
Key Buzzwords	”3-day measles”, postauricular LAD. Congenital: PDA, cataracts, deafness.	Koplik spots, 3 C’s, SSPE (late complication).	Sandpaper rash, strawberry tongue, Pastia’s lines (linear petechiae in flexures).	Slapped cheeks, aplastic crisis (in SCD), hydrops fetalis.	Fever first, then rash. Febrile seizures common.	Pruritic vesicles in crops, Tzanck smear shows multinucleated giant cells. Reactivates as shingles.
Tx	Supportive. MMR vaccine for prevention.	Supportive, Vit A. MMR vaccine for prevention.	Penicillin or Amoxicillin (to prevent rheumatic fever).	Supportive.	Supportive.	Supportive. Acyclovir in teens/adults/immunocompromised. Live-attenuated vaccine.

Fever-rash relationship

• Measles (Rubeola): Fever first (with cough, coryza, conjunctivitis) → Rash appears 3-5 days later, spreading from head to toe.
• Rubella (German Measles): Low-grade fever → Rash appears 1-2 days later, spreading quickly from head to toe.
• Scarlet Fever: Fever and sore throat begin together → “Sandpaper” rash appears 1-2 days later.
• Erythema Infectiosum (Fifth): Low-grade fever/prodrome resolves → “Slapped cheek” rash appears days later.
• Roseola Infantum (Sixth): High fever for 3-5 days → Fever breaks → Rash appears after the fever is gone.
• Varicella (Chickenpox): Fever and vesicular rash appear at the same time (lesions in various stages).