In the dermatology clinic, a 20-year-old man presents who has been referred from the primary care clinic with a diagnosis of pityriasis rosea. He has a rash that looks like pityriasis rosea, but he complains of fevers, myalgias, and swollen lymph glands. He remembers having an ulcer on his penis several months ago. What test do you recommend?

The eruption of secondary syphilis can mimic pityriasis rosea, though patients often have systemic manifestations such as fever, lymphadenopathy, headache, or bone pain. Unlike pityriasis rosea, secondary syphilis often involves the palms, soles, and mucous membranes. A sexual history should be elicited in such patients, and a rapid plasma reagin (RPR) or Venereal Disease Research Laboratory (VDRL) test should be obtained. Because syphilis is readily treated, and because untreated syphilis can result in life-threatening cardiovascular and neurologic sequelae, many dermatologists customarily obtain an RPR or VDRL test on every sexually active patient who presents with a pityriasis rosea–like eruption.