Differential Diagnosis for a 12-month-old with Allergic Rash

• Single most likely diagnosis
  • Atopic dermatitis (eczema): This is the most common allergic rash in infants, characterized by itchy, inflamed skin, and is often associated with other atopic diseases such as asthma and allergies.
• Other Likely diagnoses
  • Contact dermatitis: This occurs when the skin comes into contact with an allergen or irritant, leading to a rash. Common culprits include soaps, detergents, and certain metals.
  • Urticaria (hives): These are raised, itchy welts that can appear anywhere on the body and are often triggered by an allergic reaction to food, insect bites, or medications.
  • Seborrhoeic dermatitis: A common skin condition causing a red, itchy, and flaky rash, typically on the scalp, but can also appear on the face and body.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Anaphylaxis: A severe, life-threatening allergic reaction that requires immediate medical attention. Symptoms can include a rash, but also involve other systems such as the respiratory and cardiovascular systems.
  • Meningococcemia: A rare but potentially deadly infection caused by Neisseria meningitidis, which can present with a rash, fever, and other systemic symptoms.
• Rare diagnoses
  • Wiskott-Aldrich syndrome: A rare genetic disorder characterized by eczema, thrombocytopenia, and recurrent infections.
  • Job syndrome (Hyper-IgE syndrome): A rare condition marked by elevated IgE levels, eczema, and recurrent skin and pulmonary infections.
  • Kawasaki disease: An acute febrile illness of childhood, characterized by a rash, fever, and other systemic symptoms, which can lead to cardiac complications if not treated promptly.