Photo Rounds

Pruritic rash

A 48-year-old Hispanic man visited the dermatology clinic with a 2-month history of a pruritic rash that was confined mainly to the trunk. Prior to the visit, he had tried topical corticosteroids and antifungals, but they hadn’t helped. His trunk showed erythematous macules and reticulate patches with interspersed thin urticarial plaques without scale. The physician performed a biopsy.

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The patient’s punch biopsy showed an unremarkable epidermis but a superficial perivascular infiltrate (predominantly plasma cells). However, further investigation prompted the physician to suspect syphilis.(The patient had revealed a history of unprotected sex with multiple women.)

A subsequent rapid plasma reagin (RPR) was elevated with a titer of 1:256. Specific treponemal antibody tests confirmed the diagnosis of syphilis. The patient’s human immunodeficiency virus test was negative.

Syphilis, a systemic disease with varied dermatological findings, has been described as "the great imitator." Although it is on the list of differential diagnoses for multiple conditions, it is rarely the culprit—especially given how uncommon it has become in 20th century medicine. However, beginning in 2002, its incidence started to rise, reaching 4.6/100,000 in 2009.

Treatment for syphilis depends upon the stage of infection, which can range from the primary stage (10-90 days following exposure) to the late latent (>1 year of no symptoms) and tertiary stages (months to years after infection).

Given the nebulous history of the patient’s exposure, the physician treated the patient as having late latent syphilis and administered 2.4 million units benzathine penicillin G IM weekly for 3 weeks. After this treatment course, the pruritic lesions resolved and the patient’s RPR titer dropped to 1:8 in 3 months.

Adapted from: Mattei PL, Johnson RP, Beachkofsky TM, et al. Photo Rounds: Pruritic rash on trunk. J Fam Pract. 2011;60:539-542.

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