Differential Diagnosis

The patient's presentation of transient, red patches with white blotches or welts, along with a history of constipation, recurrent infections, and recent environmental changes, suggests a multifactorial etiology. The following differential diagnoses are considered:

• Single Most Likely Diagnosis

  • Urticaria: This is the most likely diagnosis given the description of transient, red patches with white blotches or welts that appear and disappear rapidly on various parts of the body. Urticaria can be triggered by infections, allergies, or environmental factors, which aligns with the patient's history of recurrent infections and recent preschool attendance.

• Other Likely Diagnoses

  • Allergic Reaction: An allergic reaction to food, environmental allergens (e.g., from the pellet stove), or other substances could explain the skin findings and gastrointestinal symptoms.
  • Viral Exanthem: A viral infection could cause the skin rash and systemic symptoms such as vomiting and poor oral intake.
  • Contact Dermatitis: Direct contact with an irritant or allergen could result in the observed skin changes, especially given the recent introduction of a pellet stove and potential for new environmental exposures.

• Do Not Miss Diagnoses

  • Meningococcemia: Although less likely, meningococcemia is a life-threatening condition that can present with a rash, and it is crucial to consider this diagnosis, especially in a pediatric patient with a history of recurrent infections.
  • Kawasaki Disease: This condition can cause rash, fever, and other systemic symptoms, and it is essential to rule out Kawasaki disease due to its potential for serious cardiac complications.
  • Septicemia: Any pediatric patient presenting with a rash and systemic symptoms such as vomiting and poor oral intake should be evaluated for sepsis, as it is a life-threatening condition requiring immediate intervention.

• Rare Diagnoses

  • Erythema Multiforme: A skin condition characterized by target lesions, which could be considered if the rash has a distinctive targetoid appearance.
  • Juvenile Rheumatoid Arthritis (JRA): Although rare, JRA can present with rash and systemic symptoms, and it should be considered in the differential diagnosis of a pediatric patient with unexplained rash and joint symptoms.
  • Autoimmune Disorders: Conditions such as lupus or dermatomyositis are rare in pediatric patients but could present with skin manifestations and systemic symptoms, warranting consideration in the differential diagnosis.