Pityriasis rosea and the need for a serologic test for syphilis.

A rapid plasma reagin (RPR) test was performed in fifty patients with a clinical diagnosis of pityriasis rosea to determine the frequency of syphilis as the underlying cause of the eruption. In none of the fifty patients was syphilis the cause. Experience in diagnosing skin diseases, frequency of syphilis in the community served, and the characteristics of the individual eruption are important factors in the decision to perform an RPR test.