Unilateral Rash in a Toddler

Introduction. A 15-month-old girl with a 1-week history of a non-pruritic rash on the left arm and trunk was brought to the dermatologist by her mother.

History. The patient was born prematurely at 35 weeks via emergency cesarean delivery and has no significant medical history other than a history of eczema, which was not flaring on the day of presentation. The patient’s mother stated that the patient had an upper respiratory infection 2 weeks prior to presentation, followed by this non-pruritic mild rash the next week. The mother noted that her daughter did not have a fever, chills, history of seasonal allergies or allergies to any medication, nor any other symptoms. Additionally, she was not taking any oral medication.

The mother applied desonide 0.05% topical ointment and crisaborole 2% topical ointment twice a day, which did not clear the rash. The patient was alert, interactive, and cooperative during the exam.  She was afebrile and in no distress.  Her physical examination was unremarkable except for multiple coalescent small erythematous papules with a surrounding halo in a unilateral distribution on the left rib cage (fig. 1) and left anterior medial proximal upper arm. On her right side, there were sparing features on the face, palms, flank, and soles.


Figure 1. Multiple coalescent small erythematous papules with a surrounding halo distributed on the left rib cage and left anterior medial proximal upper arm.

Figure 2. Sparing features of the rash on the right flank.