Photo Rounds

Itchy rash on forearms

A 35-year-old woman presented to her family physician (FP) with a rash that had been on both forearms for 3 months. She said that the itching had become quite bothersome. Over-the-counter hydrocortisone and antifungal creams were not helping. She was otherwise in good health.

What’s your diagnosis?


The FP strongly suspected that this was a case of nummular eczema, based on the round shape of the plaques, but the location of the lesions suggested psoriasis. The FP also considered tinea corporis with psoriasis in the differential.

The FP checked the patient's scalp, nails, and umbilicus for other signs of psoriasis and found none. He also performed a potassium hydroxide (KOH) preparation, which was negative for hyphae and fungal elements. (See a video on how to perform a KOH preparation here: To be sure that this wasn’t psoriasis, the FP also performed a punch biopsy. (The pathology subsequently came back positive for nummular eczema.) Ultimately, the yellow crusting, along with the round shape of the plaques, supported a diagnosis of nummular eczema. (“Nummus” is Latin for “coin.”)

Treatment for nummular eczema typically includes clobetasol, an ultra-high-potency corticosteroid. (The patient’s lack of response to the over-the-counter [1%] hydrocortisone was not unusual for nummular eczema because it is a low-potency steroid.) The FP in this case prescribed 0.05% clobetasol ointment to be applied twice daily to the lesions until the follow-up appointment 10 days later. At follow-up, the patient reported that the itching had almost completely resolved and the lesions were looking much better. The stitch from the biopsy was removed and the patient was told to continue using the clobetasol until the lesions completely resolved.

Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Wah Y, Usatine R. Eczema. In: Usatine R, Smith M, Mayeaux EJ, et al, eds. Color Atlas of Family Medicine. 2nd ed. New York, NY: McGraw-Hill; 2013.

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