Differential Diagnosis for Expanding Rash in a 9-Month-Old Boy
Single Most Likely Diagnosis
- A) Atopic dermatitis: This is the most likely diagnosis given the age of the patient, the description of the rash as expanding and involving the face and trunk, and the behavior of continuous scratching. Atopic dermatitis is a common condition in infants, characterized by itchy, inflamed skin, and often starts on the face and trunk before spreading.
Other Likely Diagnoses
- E) Impetigo: A contagious skin infection that can cause red sores on the face and trunk, which could fit the description of an expanding rash. It's common in children and can be itchy.
- H) Poison ivy dermatitis: Although less common in infants due to limited exposure, poison ivy dermatitis can cause an itchy, expanding rash. However, a history of exposure to poison ivy would be expected.
- J) Urticaria: Hives can cause itchy rashes that can appear anywhere on the body, including the face and trunk. They can be acute or chronic and have various causes.
Do Not Miss Diagnoses
- D) Herpes simplex: Although less likely given the description, herpes simplex infection can cause severe skin lesions and should be considered, especially if there are vesicular components to the rash or if the child is systemically unwell.
- F) Mucocutaneous lymph node syndrome (Kawasaki disease): This condition is characterized by fever, rash, swelling of hands and feet, conjunctivitis, and cervical lymphadenopathy. While the rash can be variable, the presence of other systemic symptoms would raise suspicion for Kawasaki disease, which is a medical emergency due to its potential to cause coronary artery aneurysms.
Rare Diagnoses
- B) Cellulitis: An infection of the skin and subcutaneous tissues, usually caused by bacteria. It's less likely given the description of the rash as expanding over months without mention of acute onset or systemic signs of infection.
- C) Chickenpox: Typically presents with a vesicular rash in different stages of healing, fever, and malaise. The rash description and age of the child do not strongly support this diagnosis.
- G) Nevus flammeus: A congenital vascular malformation that presents as a port-wine stain, which does not fit the description of an expanding, itchy rash.
- I) Tinea capitis: A fungal infection of the scalp, which would not explain the rash on the face and trunk unless the child has a more widespread fungal infection, but this would be unusual and not the first consideration based on the description provided.