Comparative analysis of immunohistochemistry, polymerase chain reaction and focus-floating microscopy for the detection of Treponema pallidum in mucocutaneous lesions of primary, secondary and tertiary syphilis.

BACKGROUND: The incidence of syphilis is increasing in many parts of the world including a re-emergence in Western Europe and North America. Depending on the disease stage, direct detection of Treponema pallidum in mucocutaneous lesions of syphilis may be difficult and histopathological findings are not always straightforward. Thus, the correct histological diagnosis may be challenging.

OBJECTIVES: Comparatively to evaluate the evidence for infection with T. pallidum by immunohistochemistry (IHC), polymerase chain reaction (PCR) and focus-floating microscopy (FFM).

METHODS: A series of 86 paraffin-embedded skin biopsy samples from patients with primary, secondary or tertiary syphilis was assessed for detection of T. pallidum by IHC and FFM; 45 specimens were also investigated by a T. pallidum-specific PCR analysis. Histopathological reaction patterns and number and distribution of treponemes were studied, and all data were re-evaluated by clinicopathological correlation.

RESULTS: Using a polyclonal antibody directed against T. pallidum, we detected the presence of T. pallidum by IHC in 42/86 (49%) samples [6/9 (67%) primary, 34/62 (55%) secondary and 2/15 (13%) tertiary syphilis]. T. pallidum-specific DNA was detected in 31/45 (69%) specimens [4/4 (100%) primary, 26/34 (76%) secondary and 1/7 (14%) tertiary syphilis]. In comparison, FFM analysis resulted in an overall detection rate of 82/86 (95%) [9/9 (100%) primary, 60/62 (97%) secondary and 13/15 (87%) tertiary syphilis]. Significant differences were observed concerning amount and distribution of organisms (epitheliotropic vs. endotheliotropic) in correlation to the three disease stages and to histopathological reaction patterns.

CONCLUSIONS: FFM is a highly sensitive and specific method to detect T. pallidum in tissue from mucocutaneous syphilis lesions. Our results indicate that a combination of PCR and FFM, as the most sensitive approach, could provide an additional benefit for the histopathological diagnosis of (late) secondary and tertiary syphilis and may be helpful in cases where serological testing of T. pallidum antibodies has failed, but the clinical suspicion for syphilis remains.