Pruritic rash on trunk
The patient had been treated with topical antifungals and steroids without relief, but a more detailed history suggested a serious infectious etiology.
The differential included urticaria and lupus erythematosus
The differential diagnosis for our patient included urticaria, telangiectasia macularis eruptiva perstans, subacute cutaneous lupus erythematosus, and mycosis fungoides. All of these conditions can be distinguished from secondary syphilis by serology and/or biopsy.
Urticaria is a common dermatologic problem with numerous etiologies. It presents as pruritic raised edematous erythematous wheels that blanch with pressure. Although it affects 15% to 25% of the general population at least once in their lives,3 it may progress to life-threatening anaphylaxis. Isolated acute urticaria usually responds to oral antihistamines.
Telangiectasia macularis eruptiva perstans is a form of cutaneous mastocytosis that appears as persistent macules that are red to brown and may exhibit telangiectasia.4 Systemic disease may be evaluated using serum tryptase levels. Patients without systemic disease are managed with oral antihistamines.
Subacute cutaneous lupus erythematosus (SCLE) often presents precipitously as erythematous maculopapular lesions that may coalesce into annular or papulosquamous plaques.5 It has a predilection for sun-exposed areas and is more common in women.5 Multiple drugs have been associated with SCLE, including phenytoin, calcium channel blockers, and thiazide diuretics.6 Treatment consists of discontinuing the offending drug (if one is identified), avoiding (or protecting against) sun exposure, and using topical corticosteroids, oral corticosteroids, and/or antimalarials.
Mycosis fungoides is a form of primary cutaneous T-cell lymphoma that more commonly affects males.7 It begins as erythematous pruritic patches that typically involve the sun-spared areas of the lower abdomen and proximal extremities; it progresses slowly.7 As lesions develop into plaques, they may appear psoriasiform. Treatment depends on the stage of the disease and ranges from topical corticosteroids to systemic radiation and chemotherapy.8
Serology greatly aids diagnosis
If syphilis is not treated during the primary stage, it may progress directly into latency or into the second stage of infection. Preventing progression into late findings hinges upon proper diagnostics. While the initial suspicion should begin with history and physical examination, serology is most frequently used to confirm the presence of Treponema pallidum.
It may take as long as 3 weeks after the appearance of the primary chancre for serology to become positive.9 During this interval, directly visualizing the pathogen via dark-field microscopy may be useful. Following this interval, nontreponemal serology such as the RPR and venereal disease research laboratory (VDRL) are frequently used as the initial serology. These rapid tests detect the antibody to cardiolipin and are relatively inexpensive.
Infection is confirmed with specific treponemal tests, including the fluorescent treponemal antibody absorption (FTA-abs), treponemal enzyme immunoassay, and treponemal particle agglutination tests. These tests are specific for T pallidum and confirm a positive RPR or VDRL. However, specific treponemal tests will not differentiate syphilis from nonvenereal treponematoses such as Bejel, Yaws, and Pinta.10
The common belief is that nontreponemal tests may become negative after successful treatment, and treponemal tests will remain positive indefinitely after successful treatment. However, a study found that 28% of patients treated during primary syphilis and 44% of patients treated during secondary syphilis had positive nontreponemal tests 3 years after treatment.11 In the same study, nearly a quarter of patients treated during primary syphilis no longer had positive FTA-abs 3 years after treatment.11
