Chapter 39. Mineral Oil Preparation: Diagnosing Scabies

• Suspected Sarcoptes scabiei infestation; the diagnosis should be verified because it is often overdiagnosed.

• Glass microscope slide.

• Mineral oil.

• Cotton-tipped applicator.

• Microscope.

• #15 scalpel blade or other device to scrape skin.

• Minimal discomfort and bleeding with vigorous scraping.

• Scrape burrows or unexcoriated papules.

• The highest yield of mites, eggs, or fecal pellets is from the burrows, which are most commonly found on hands or feet.

• If many family members have lesions, perform the scraping on the parents, who are often more cooperative and less fearful than infants or young children.

• Treatment includes eradication of the mites on the patient, treatment of associated problems (pruritus, scabietic nodules), treatment of personal contacts, and destruction of the mite in the patient’s surroundings.

• Parents and patients should be aware that scraping may cause minimal bleeding and mild discomfort.

• Patient should be positioned in good lighting with access to lesion to be tested.

• Drop mineral oil on to a sterile blade or the lesion itself with a cotton-tipped applicator.

• Vigorously scrape the lesion 5–6 times until it is unroofed. This may produce bleeding.

• Collect material from as many lesions as possible, preferably from burrows.

• Transfer material from each lesion to the slide, add a few more drops of mineral oil, and cover with the coverslip (Figure 39–1).

• Scan slide on low-power objective.

• Diagnosis is made by seeing the mite itself (0.2–0.4 mm in size), mite parts, eggs (oval and one-tenth the size of the mite), egg cases, or golden-brown fecal pellets (scybala).

• Feces and eggs are easier to find than mites. Feces often occur in clumps.

• Air bubbles (usually round) are an artifact that can be mistaken for eggs. Gently press on coverslip to dislodge these.

• If treated adequately, follow-up is not indicated.

• Pruritus may persist for weeks or months in patients even after adequate therapy.