About This Page
This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Measles: cough, coryza, conjunctivitis, Koplik spots, cephalocaudal morbilliform rash, high fever, airborne isolation
- Rubella: mild fever, posterior auricular/suboccipital lymphadenopathy, fine rash; congenital infection is the major concern
- Roseola: high fever for 3-5 days followed by rash as fever resolves; associated with febrile seizures
- Erythema infectiosum: parvovirus B19, slapped-cheek rash, lacy body rash; dangerous in pregnancy and hemolytic anemia
- Hand-foot-mouth: oral ulcers plus vesicles on hands/feet; scarlet fever: GAS pharyngitis with sandpaper rash and strawberry tongue
Overview
Childhood exanthems are common Step 2 CK pattern-recognition diagnoses. The key is not memorizing every rash but anchoring the timing, prodrome, mucosal findings, lymph nodes, distribution, vaccination status, and complications. Some exanthems are benign and supportive-care only; others require isolation, public health action, antibiotics, or pregnancy counseling.
Epidemiology
Vaccination has made measles and rubella uncommon in highly immunized populations, but outbreaks occur with under-immunization and travel. Roseola and hand-foot-mouth disease are common in young children. Parvovirus B19 spreads in school-aged children. Scarlet fever reflects toxin-mediated group A streptococcal infection and requires antibiotic treatment.
Clinical Features
Symptoms
Fever with rash and viral prodrome
Cough, coryza, conjunctivitis, photophobia, or Koplik spots suggesting measles
Sore throat, fever, abdominal pain, and sandpaper rash suggesting scarlet fever
Oral pain/refusal to drink with hand/foot vesicles suggesting hand-foot-mouth disease
Rash after fever resolves in toddler suggesting roseola
Pregnancy exposure to rubella or parvovirus B19 is high-risk
Signs
Morbilliform rash starting on face/hairline and spreading downward in measles
Posterior auricular/suboccipital lymphadenopathy with rubella
Slapped-cheek rash with lacy reticular rash on trunk/extremities in parvovirus B19
Vesicles on palms/soles and painful oral ulcers in hand-foot-mouth disease
Strawberry tongue, circumoral pallor, Pastia lines, and sandpaper rash in scarlet fever
Toxic appearance, petechiae/purpura, neck stiffness, or mucosal sloughing are red flags for serious alternative diagnoses
Investigations
First-line
Clinical diagnosisMost exanthems are diagnosed by characteristic pattern and exposure history
Vaccination and exposure historyAssess MMR status, travel, outbreak exposure, school/daycare contacts, pregnancy contacts
Rapid strep test/throat cultureFor suspected scarlet fever or GAS pharyngitis
Second-line
Measles PCR/serology and public health notificationSuspected measles requires airborne isolation and immediate public health involvement
Rubella or parvovirus serologyUseful for pregnancy exposure, outbreak investigation, or unclear diagnosis
CBC/reticulocyte countIf parvovirus exposure in hemolytic anemia or immunocompromised host
Specialist
Public health/infectious diseasesSuspected measles, rubella, outbreak, immunocompromised host, or pregnancy exposure
Obstetrics/maternal-fetal medicinePregnant exposure to rubella or parvovirus B19
1
Measles
- Airborne isolation immediately if suspected; notify public health
- Supportive care plus vitamin A in severe disease or high-risk children per public health guidance
- Post-exposure prophylaxis: MMR within 72 hours or immune globulin within 6 days for eligible high-risk contacts
2
Rubella and roseola
- Rubella is usually mild in children but dangerous in pregnancy; isolate and notify public health if suspected
- Roseola is supportive care; fever resolves before rash appears and febrile seizure may occur
3
Parvovirus B19 and hand-foot-mouth
- Parvovirus is supportive in healthy children; evaluate aplastic crisis in hemolytic anemia and fetal hydrops risk in pregnancy
- Hand-foot-mouth disease is supportive with hydration and analgesia; avoid dehydration from painful oral ulcers
4
Scarlet fever
- Treat GAS pharyngitis/scarlet fever with penicillin or amoxicillin; alternatives for allergy according to guideline
- Antibiotics prevent acute rheumatic fever and reduce transmission
- Children can usually return to school after afebrile and at least 12-24 hours of appropriate antibiotics depending local policy
Complications
- Measles complications: Otitis media, pneumonia, encephalitis, and subacute sclerosing panencephalitis
- Congenital rubella syndrome: Sensorineural deafness, cataracts, PDA, and neurodevelopmental impairment
- Parvovirus aplastic crisis: Severe anemia in sickle cell disease or other hemolytic disorders; fetal hydrops in pregnancy
- Dehydration: Hand-foot-mouth oral ulcers can prevent intake
- Acute rheumatic fever: Preventable complication of untreated GAS pharyngitis/scarlet fever
USMLE Step 2 CK Exam Tips
- 1Measles = cough, coryza, conjunctivitis, Koplik spots, cephalocaudal rash
- 2Roseola = high fever that resolves, then rash appears; febrile seizure association is classic
- 3Parvovirus B19 = slapped cheek + lacy rash; dangerous in pregnancy and hemolytic anemia
- 4Rubella = posterior auricular/suboccipital lymphadenopathy; congenital rubella is the real concern
- 5Hand-foot-mouth = oral ulcers plus palm/sole vesicles, usually coxsackie/enterovirus
- 6Scarlet fever = sandpaper rash + strawberry tongue after GAS pharyngitis; treat with penicillin/amoxicillin
- 7Suspected measles requires airborne isolation and public health notification
practicetest your knowledge on common childhood exanthems (measles, rubella, roseola, erythema infectiosum, hand-foot-mouth, scarlet fever)Apply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — pediatrics and beyond.
open q-bank