Photo Rounds

Rash on arms and legs

A 40-year-old man went to see his family physician (FP) about a rash on his arms and legs that had developed 4 weeks earlier. The patient’s hands and the soles of his feet were clear, and he denied any itching, fever, or pain. He said that he’d had unprotected sex with 2 female partners in the last 3 months. He denied having any penile ulcers at the time or in the recent past. He also denied any penile discharge. A rapid plasma reagin (RPR) test came back negative.

What’s your diagnosis?


Based on the negative RPR test and the results of a subsequent 4-mm punch biopsy, the FP made a diagnosis of pityriasis rosea. The trunk is typically more involved in this condition, making this case (involvement of arms and legs) a type of inverse pityriasis rosea.

Because secondary syphilis can also present as a papulosquamous eruption, it can be difficult to distinguish from pityriasis rosea on clinical grounds. Therefore, taking a sexual history is important when a diagnosis of pityriasis rosea is being considered. In patients with a history of sexually transmitted diseases (STDs) or high-risk sexual practices, an RPR test should be ordered.

The patient in this case was relieved to learn that he didn’t have an STD and said he’d be more careful in the future. The FP assured him that the condition would go away spontaneously and that no medications would be needed.

Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Henderson D, Usatine R. Pityriasis rosea. In: Usatine R, Smith M, Mayeaux EJ, et al, eds. Color Atlas of Family Medicine. 2nd ed. New York, NY: McGraw-Hill; 2013: 896-900.

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