Dermoscopy as a clinical tool for the diagnosis of demodicosis: a retrospective intrapatient case-control study

Dermoscopy has been used for the non-invasive diagnosis of demodicosis. Several studies have evaluated the usefulness of this tool in the diagnosis, however, there are differences in the gold standard (SSSB or KOH test) and criteria of positivity used between studies. Added to this, is the lack of controls and objective quantification of the usefulness of dermoscopic signs in clinically observable and relevant ranges. To validate the usefulness of dermoscopy for the diagnosis of demodicosis by calculating the performance indicators for the different dermoscopic signs. Retrospective intrapatient case-control study, which included adults with suspicion of demodicosis. Dermoscopic photographs and scraping of healthy and lesional skin were obtained. Samples were analyzed microscopically by trained personnel. Photographs were evaluated by determining the presence of Demodex tails (DT), dilated follicular openings (DFO) and dilated blood vessels (DBV) in pre-defined ranges. 64 patients were included (total = 256 samples); the presence of demodex on skin scraping was seen in 69%. Under dermoscopy, the presence of DT in range 11-20/field had a positive likelihood ratio (LR) of 12.10 (95%CI 6.52-22.45) and negative LR 0.32 (95%CI 0.23-0.45). Combined and dichotomized performance for at least one positive sign under dermoscopy (DT > 10/field, DFO > 10/field or DBV > 50% of the field): positive LR 7.14 (95%CI 4.80-10.62) and negative LR 0.11 (95%CI 0.06-0.22). The presence of DT, DFO or DBV has a high correlation with a positive mite test, so the diagnosis of demodicosis could be made only through dermoscopy.