A 3-month-old boy presented with a circular rash that appeared after routine immunizations at 2 months of age. He was born by cesarean delivery to a 40-year-old mother (gravida 10, para 5) after an uneventful prenatal course. The rash had gradually expanded from the injection site. The patient had no fevers or problems with feeding and had not recently traveled. His weight gain and development were appropriate. There was no family history of autoimmune disorders, and there were no similar rashes among household members.

The physical examination revealed two confluent 20 cm × 10 cm, circular, pink plaques on the anterior side of the left leg and one 10 cm × 10 cm, circular, pink plaque on the lateral side of the right leg (Figure 1). The lesions were not tender or warm and showed no signs of excoriation. The physical examination was otherwise unremarkable, and his vital signs were normal.

QUESTION

Based on the patient's history and physical examination, which one of the following is the most likely diagnosis?

• A. Contact dermatitis.

• B. Eczema (atopic dermatitis).

• C. Hyperimmunoglobulinemia E syndrome.

• D. Ringworm (tinea corporis).

• E. Vaccine reaction with dermatitis.