DermaDiagnosis
Slow and Steady: A Worrisome Pace
The slow, steady growth of the flat, asymptomatic lesion on his right deltoid area concerns this 43-year-old man. His primary care provider...
ANSWER
The correct answer is pityriasis rosea (choice “d”).
Virtually all patients with this condition believe that they have a terrible case of “ringworm” (ie, fungal infection; choice “a”)—an opinion all too often corroborated by the medical provider unacquainted with pityriasis rosea. The two can be difficult to distinguish, but the “herald” patch, oval shape, odd color, and fine scale all serve to confirm the diagnosis. When necessary, a KOH prep or biopsy can be done.
Psoriasis (choice “b”) can manifest acutely, but it is distinctly salmon-pink under coarse, white scale that affects the palms, nails (with pits), and scalp. Psoriasis lesions are round (rather than oval), with coarser scale and without a herald patch.
The lack of antecedent sores and denial of sexual contact ruled out secondary syphilis (choice “c”). Patients with secondary syphilis often present with low-grade fever, malaise, and palmar scaly papules—all of which were missing in this case. Syphilis serology (rapid plasma reagin) can be easily obtained if doubt persists.
DISCUSSION
Pityriasis rosea (PR) is a papulosquamous eruption that is common in younger populations. About 40% of affected patients present with a large scaly lesion, which is followed by the appearance of multiple smaller oval lesions within days. In most cases, PR is fairly easy to diagnose: the lesion’s oval shape, pinkish-brown color, centripetal fine scale, herald patch, and adherence to skin tension lines are all characteristic findings.
Though the exact organism has not been identified, PR is almost certainly viral in origin. Like many viral exanthems, occurrence tends to peak in the spring and fall. There are also indications that the body builds immunity to the infection, since recurrence outside the acute phase is rare.
Treatment options are unsatisfactory, though exposure to UV sources appears to help. Patients must be informed that their condition will, unfortunately, last for at least six to nine weeks, during which crops of lesions will come and go.
