Accuracy of standard dermoscopy for diagnosing scabies
Scabies is a contagious skin infestation caused by the human mite Sarcoptes scabiei. The usual reference method for definitive diagnosis is ex vivo identification of the mite with microscopic examination of skin scrapings. We compared diagnostic accuracy of in vivo dermoscopic (DS) mite identification using a pocket handheld low-magnification DS with the reference method.
We conducted a prospective, nonrandomized, evaluator-blinded, noninferiority study to compare sensitivities (main outcome) and other diagnostic properties of DS and microscopic examination of skin scrapings. Among 756 patients with a presumptive diagnosis of scabies consulting in one center, 238 were sequentially submitted to the two diagnostic procedures. Three dermoscopists (one expert, two inexperienced) were involved. Diagnostic strategies using clinical skills only, DS results, and a combination of both were compared.
Sensitivities were 91% (95% confidence interval: 86-96) for DS and 90% (95% confidence interval: 85-96) for microscopic examination of skin scrapings (P = .005 for noninferiority). Specificities were 86% (95% confidence interval: 80-92) for DS and 100% (by definition) for microscopic examination of skin scrapings. DS sensitivities were similar for the expert and inexperienced dermoscopists, whereas differences were observed in specificities. However, diagnostic accuracy of inexperienced dermoscopists steadily increased during the study. Compared with clinical-based, DS-based treatment decision rule minimized the number of false-positive and false-negative findings, whereas a treatment decision rule based on combination of clinical presumption and DS result drastically reduced the number of patients with scabies left untreated.
There is no definitive standard for ruling out the diagnosis of scabies.
Standard DS with a handheld DS is a useful tool for diagnosing scabies, with high sensitivity, even in inexperienced hands. It greatly enhances clinical skills for making treatment decisions.
Available from: Sang Seok Kim
- "The weight of this evidence is that dermoscopy is very useful, especially in certain circumstances. Walter et al.6 and Dupuy et al.7 evaluated the diagnostic characteristic of dermoscopy. However, to our knowledge, there have been few well-designed clinical studies concerning the diagnostic accuracy of dermoscopy by comparing skin scraping "with dermoscopy" to skin scraping "without it". "
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ABSTRACT: Scabies is a contagious skin infestation characterized clinically by nocturnal pruritus, visible burrows and contagiousness. Dermoscopy has been suggested as an alternative for diagnosing scabies. But, there have been few well-designed studies evaluating the diagnostic accuracy of dermoscopy.
We tried to confirm the diagnostic accuracy of dermoscopy for diagnosing scabies. We also tried to demonstrate specific circumstances in which dermoscopic identification of mites ("with dermoscopy") is more useful in diagnosing scabies, and to identify the specific clinical findings that could be used as a possible marker in diagnosing scabies.
We compared the scraping procedure "with dermoscopy" and "without it" in 49 patients, measuring the duration and outcome of each procedure. Also, we tried to find the specific clinical factors associated with our objects.
The skin scraping "with dermoscopy" was superior to "without it" with respect to the duration and accuracy of the procedure. A history of previous steroid treatment was associated with the superiority of dermoscopy. The correlation between the presence of visible burrows and the positive outcomes of "with dermoscopy" was statistically significant.
Skin scraping with dermoscopy is implicated as the diagnostic method of choice for scabies at the present time. Dermoscopy is especially useful in diagnosis of incognito scabies. In addition, the presence of visible burrows could be a reliable positive marker of scabies in the absence of dermoscopy or microscopy data.
Available from: Carle F Paul
- "La structure triangulaire correspond à la section antérieure pigmentée du parasite, le segment linéaire correspond au tunnel creusé par le parasite pour déposer ses oeufs . Une étude prospective récente, non randomisée, réalisée chez 756 patients dont 238 patients analysés en dermatoscopie, montre que la sensibilité de la dermatoscopie est identique à celle de l'examen parasitologique , même dans des mains inexpérimentées . Il peut être utile de répéter cet examen, en cas de négativité. "
Available from: Luc Thomas
- "La dermoscopie est une alternative de choix, permettant un diagnostic non invasif, plus rapide et précis . La dermoscopie a, à cet égard, démontré son utilité dans la démarche diagnostique  . Elle permet également de guider les prélèvements à la recherche du sarcopte. "
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