Differential Diagnosis for 8-year-old with Cough, Maculopapular Rash, Fever, and Conjunctivitis

• Single most likely diagnosis:
  • Roseola (Exanthem Subitum): Although it typically starts on the trunk, the presence of a maculopapular rash, fever, and the fact that the child is fully vaccinated make this a strong consideration. The rash in roseola can sometimes spread to the limbs.
• Other Likely diagnoses:
  • Measles: Despite being fully vaccinated, vaccine failure or exposure to a large dose of the virus could lead to infection. Measles starts with fever, cough, conjunctivitis, and then a maculopapular rash that spreads from the head down to the limbs.
  • Enteroviral Infection: Enteroviruses can cause a variety of rashes and symptoms, including fever, cough, and conjunctivitis. The rash can appear anywhere on the body, including the arms and legs.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • Meningococcemia: This bacterial infection can present with fever, rash (which can be maculopapular and start anywhere, including the limbs), and conjunctivitis. It's critical to consider this diagnosis due to its high mortality rate if not promptly treated.
  • Kawasaki Disease: Although more common in younger children, Kawasaki disease can present with fever, rash, conjunctivitis, and can involve the limbs. It's a critical diagnosis to consider due to the risk of cardiac complications.
• Rare diagnoses:
  • Scarlet Fever: Caused by Group A beta-hemolytic streptococci, it presents with a rash (typically starting on the trunk), fever, and can have a cough if there's associated streptococcal pharyngitis. The rash can spread to the limbs.
  • Erythema Infectiosum (Fifth Disease): Characterized by a "slapped cheek" appearance, it can also cause a maculopapular rash on the limbs. However, the presence of cough and conjunctivitis is less typical for this condition.