Practice Gap
The Sarcoptes scabiei mite is a microscopic organism that causes scabies in the human host. The scabies mite is highly transmissible, making scabies a common disease in heavily populated areas. The mite survives by burrowing into the epidermis, where it feeds, lays eggs, and defecates.1
The rash in the host represents an allergic reaction to the body of the scabies mite, producing symptoms such as intense itching, rash, and erosions of the skin. The scabies rash tends to occur in warm and occluded areas of the body such as the hands, axillae, groin, buttocks, and feet.1,2
Delaying treatment of scabies can be hazardous because of the risk of rapid spread from one person to another. This rapid spread can be debilitating in specific populations, such as the immunocompromised, elderly, and disabled.
Mineral oil preparation is the classic method used to identify scabies (Figure 1). This method relies on obtaining mites by applying mineral oil to the skin and using a 15-mm blade to scrape off layers of the affected skin. The scraped material is spread onto a microscope slide with mineral oil, a coverslip is applied, and the specimen is analyzed by direct microscopy. This method proves only as effective as knowing where the few mites are located.
FIGURE 1. Sarcoptes scabiei mineral oil preparation (original magnification ×400). Microphotograph courtesy of Steven Daveluy, MD (Detroit, Michigan).
At any time, only 10 to 12 mites live on a human host.3 Therefore, it can be challenging to obtain a mite for diagnosis because the location of the skin mites may be unknown. Dermoscopy can be used to locate burrows and other signs of S scabiei. With a dermatoscope, the scabies mite can be identified by the so-called delta-wing jet sign.4
However, dermoscopy is not always successful because extensive hemorrhagic crusting and erosions of the skin secondary to constant scratching can obscure the appearance of burrows and mites. Because patients are constantly scratching areas of irritation, it is possible that S scabiei can be located under the fingernail of the dominant hand.
The Technique
To address this practice gap, a mineral oil scabies preparation can be performed by scraping under the fingernail plate at the level of the hyponychium. Mites might accumulate underneath the fingernails of the dominant hand when patients scratch the area of the skin where S scabiei mites are burrowing and reproducing.