Comparison of dermoscopy, skin scraping, and the adhesive tape test for the diagnosis of scabies in a resource-poor setting

Abstract

Background: Scabies is a parasitic skin disease endemic in resource-poor communities in low-income countries. The best ways to diagnose scabies in this setting have not been investigated.

Objective: To compare the diagnostic properties of dermoscopy, the microscopic examination of a skin scraping, and the adhesive tape test in 125 patients with a presumptive diagnosis of scabies.

Design: A prospective evaluator-blinded study.

Results: The sensitivity of dermoscopy was 0.83 (95% confidence interval [CI], 0.70-0.94) and significantly higher than the sensitivity of the adhesive tape test (0.68; 95% CI, 0.52-0.81; P < .001). The sensitivity of skin scraping was low (0.46; 95% CI, 0.31-0.62). The specificity of dermoscopy was 0.46 (95% CI, 0.34-0.58); by definition, it was 1.00 for skin scraping and the adhesive tape test. The negative predictive value was identical for dermoscopy and the adhesive tape test (0.85; 95% CI, 0.69-0.94 and 0.75-0.91, respectively) but significantly lower for skin scraping (0.77; 95% CI, 0.67-0.84; P < .001). The sensitivity of dermoscopy increased with the severity of the disease, whereas the sensitivity of the adhesive tape test did not depend on this characteristic. Limitations Because of active case finding, the duration of the infestation was short and the severity of disease was rather low in most patients. The rather short duration of the infestation might have affected the diagnostic properties of each test in different ways.

Conclusions: When trained personnel are available, dermoscopy is a valid tool for diagnosing scabies in a resource-poor setting. The adhesive tape test is easy to perform and, because it has high positive and negative predictive values, the test is ideal for screening purposes. Skin scraping cannot be recommended as a diagnostic tool in this setting.