Seronegative secondary syphilis in a patient infected with the human immunodeficiency virus (HIV) with Kaposi sarcoma. A diagnostic dilemma.

Reagin and treponemal antibody tests are highly reliable in diagnosing secondary syphilis. However, patients infected with the human immunodeficiency virus (HIV) respond abnormally to antigenic stimulation and may fail to develop typical serologic responses to infections. We report the case of an HIV-infected man with Kaposi sarcoma and secondary syphilis whose VDRL test and fluorescent treponemal antibody-absorbed test were repeatedly nonreactive. Correct diagnosis required biopsy of a skin lesion with silver staining to show spirochetes. Clinicians treating HIV-infected patients should be aware of the problems of serologic diagnosis of syphilis in these patients. Biopsy samples of appropriate tissues and staining for spirochetes may be needed to arrive at the correct diagnosis.