Nummular Eczema of the Diaper Area

This 9-month-old boy was brought to dermatology by his parents, who were alarmed by the rash on his buttocks. The rash had been present on and off for several weeks and had been treated as ringworm, first with clotrimazole then with terbinafine cream, to no good effect. The rash appeared to be largely asymptomatic, but it concerned the parents nonetheless.

There was a strong family history of atopy; in fact, the child had begun to show signs of allergic rhinitis and mild reactive airway disease.

At presentation, the child was well developed and well nourished. The rash was composed of several large, arciform, papulosquamous patches on the buttocks. Scaling was distributed uniformly on the surfaces of the slightly erythematous lesions. No such lesions were seen elsewhere on his exceptionally dry skin. Results of potassium hydroxide preparation testing were negative for superficial fungal infection.

These findings all point to the likelihood that these lesions are a form of eczema, which is a common problem in atopic children, especially in the diaper area as a result of the continual wetting and drying. In this patient’s case, the eczema took on a nummular (round) morphology, leading to confusion with ringworm (dermatophytosis), which actually would be quite uncommon on this area of a child’s body. Other conditions in the differential diagnosis were psoriasis, candidiasis, and irritant/contact dermatitis, among others.

The boy’s rash was treated successfully with application of 2.5% hydrocortisone cream twice daily for 1 week.