Darkfield examination and allied procedures

Abstract

When Schaudinn and Hoffmann made the initial discovery of T. pallidum in 1905, they did so with an ordinary light microscope. The difficulty of visualizing the pale treponeme under those circumstances will become apparent immediately to anyone who cares to try it, and the virtual transparency of the organism was, of course, the feature that led to Schaudinn's choice of “pallida” (and later “pallidum”) for the species name of his find. Shortly after the discovery, several German optical firms exhibited prototypes of the newly developed darkfield microscopes, and, in 1906, Landsteiner and Mucha 1 were the first to recommend the use of these instruments to demonstrate T. pallidum. Within a year, darkfield microscopy had become almost routine in the investigation of early and congenital syphilis in the European clinics. The procedure was introduced into the United States in 1909 by Udo Wile, 2 and a survey of the literature of the period shows that by 1914 a recognition of both the strengths and weaknesses of the technique and an understanding of the morphology of the organisms likely to be encountered were remarkably complete. The strongest indications for the use of the darkfield in the current management of venereal disease exist in two special situations: 1) the investigation of lesions in suspected cases of congenital syphilis and 2) the search for organisms in suspected cases of primary syphilis, especially during the initial period of seronegativity. The procedure has lost ground in the latter situation, owing in part to the increasing effectiveness of the newer treponemal and nontreponemal tests in detecting the presence of the disease in its earliest state; but it is premature to conclude, as in the recent statement by one experienced venereologist, that “in the foreseeable future the darkfield examination will be of historical interest, except for those in research.” 3 The purpose of this section is to summarize the technique and the findings to be expected in the darkfield and other methods employed in the examination of material taken directly from early syphilitic lesions. A step-by-step method for combining the results of these procedures and the results of physical examination and serologic testing to make the diagnosis of infectious syphilis is given in Chapter 11.