This woman storms into your office, absolutely outraged (or, by the blush on her cheeks, embarrassed?). She shouts, "The other doctor accused me of having syphilis! He said a lab test even confirmed it. I can't possibly have syphilis. I haven't slept with anyone in years."Challenge: Explain.
Case idea contributed by Alex Penn.
Image is in the public domain.
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lupus- malar rash and false positive result on syphilis test
It’s Not…
The causative organism of syphilis, Treponema pallidum, cannot be cultured in the laboratory. Confirmation can be made by darkfield microscopy, fluorescent antibody staining, PCR, or most commonly, serologic tests. Nontreponemal serologic tests include the VDRL and RPR; treponemal tests include FTA-ABS and TPPA. False positive results for the nontreponemal tests occur in approximately 1% of the general population, and can be due to febrile illness, recent immunization, autoimmune disorders, IV drug use, chronic liver disease, and HIV infection. Positive results always need to be confirmed by a treponemal test (which apparently was not done in this case). Here, the characteristic malar butterfly rash on a woman suggests systemic lupus erythematosus, which commonly gives a false positive VDRL. The other signs and symptoms of lupus are varied and will not be addressed here.
Sources: UpToDate; Medline (nlm.nih.gov); Alex Penn
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