Differential Diagnosis for 16-month-old with Erythematous Macules/Plaques Rash

• Single most likely diagnosis
  • Phytophotodermatitis or Sunburn: The child was in the mountains for vacation, and the mother denies using sunscreen. The rash is present on exposed areas (face and tops of forearms) and absent where clothing was worn, suggesting a reaction to sunlight. Phytophotodermatitis, a reaction to certain plant chemicals activated by sunlight, is also possible given the outdoor setting.
• Other Likely diagnoses
  • Contact Dermatitis: This could be due to exposure to allergens or irritants in the environment, such as certain plants or substances encountered during the vacation.
  • Insect Bites or Stings: Being outdoors increases the risk of insect bites, which could cause erythematous macules or plaques.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Meningococcemia: Although the child does not have URI symptoms, meningococcemia can present with a rash and is a medical emergency. It's crucial to consider this diagnosis, especially if the child shows signs of severe illness.
  • Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN): These are severe skin conditions usually triggered by medications or infections. They can present with skin lesions and are medical emergencies.
• Rare diagnoses
  • Juvenile Spring Eruption: A rare condition that occurs in the spring, characterized by a photosensitive eruption on the faces of children.
  • Polymorphic Light Eruption (PMLE): An uncommon skin condition that occurs in response to sunlight, more common in adults but can occur in children.