Late seronegative syphilis refers to clinical signs of ocular or neurosyphilis in a patient whose routine blood (reagin) test is nonreactive, but in whom a specific treponemal test is reactive. This report documents the presence of spirochetes in aqueous humor, cerebrospinal fluid, and at liver biopsy in such patients. Spirochetes have been found in the aqueous humor with no biomicroscopic abnormality and in cerebrospinal fluids which had normal cell counts, protein levels, and reagin and colloidal gold test results. Identification of the organisms depends on use of the fluorescein antibody technique, in that spirochetes stain with fluorescein-tagged anti-Treponema pallidum globulin on ultraviolet microscopy.
Smith JL, Israel CW. The Presence of Spirochetes in Late Seronegative Syphilis. JAMA. 1967;199(13):980-984. doi:10.1001/jama.1967.03120130066011