Treponema pallidum in macular and papular secondary syphilitic skin eruptions

The ultrastructure of biopsies from dry macular and papular secondary syphilitic skin lesions of 10 patients were studied by electron microscopy. In all biopsies few diffusely distributed treponemes were observed. This may explain the difficulties in demonstrating treponemes by darkfield examination of tissue fluid from dry secondary syphilitic skin lesions. The outlines of treponemes were less distinct as compared to those of primary syphilis. The periplastic membranes were almost invariably absent and the cytoplasmic membranes appeared in close contact with an enclosing layer of irregularly demarcated, electron dense amorphous substance. This substance may be a manifestation of the immune reaction of the host cells to the treponemes. Degenerations were noted in both unmyelinated and myelinated nerve tissue. This accounts for the fact that skin lesions in secondary syphilis are usually without symptoms. Also in the vessel walls treponemes were demonstrated. The vascular endothelial cells were proliferating and the basement membranes were multilaminated and split.