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Presentation of Quiz #37

A 76-year-old assisted-living patient presented with multiple area of itchy skin. She began to notice the onset of itching in her hands and attributed the symptoms to continued dry weather and lack of hand lotion use. In spite of her using a new lotion and mild soap, the pruritus remained and began to spread to other areas of the body, including elbows, axillae, and her back. She then assumed the increased symptoms might be due to an allergic reaction to something she had been eating. Although her diet was carefully reviewed, and she refrained from eating things to which she thought she might be allergic, the symptoms became worse. At that point, she was seen by her physician.

Positive findings were limited to the skin, with evidence of intense scratching where the skin was excoriated over the hands and arms. There were also some papules seen on her back. Scrapings of some of these lesions revealed the following:

This object measured about 0.25 mm and was almost clear. There were some other structures in the specimen, but they could not be identified.

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Answer and Discussion of Quiz #37

The image presented in Diagnostic Quiz #37 is the following:

  1. This specimen from a skin scraping is representative of the itch mite, Sarcoptes scabiei. This mite is microscopic and lives in cutaneous burrows, where the fertilized female deposits eggs. The eggs hatch and develop into nymphs, which in turn develop into adults. Occasionally, eggs, or scybala (fecal pellets) can also be found in the skin scraping. It is important to remember that low light will enhance your ability to see the mite; light that is too bright may just shine through the organism, preventing morphologic details from being seen.

Comment: This is a case of a woman who had scabies, caused by the itch mite, Sarcoptes scabiei. She was treated and no new lesions appeared. Although the pruritus continued for several weeks, the use of Calamine lotion reduced the symptoms. With followup and discussion with the residents, two additional patients in the same facility were also found to have scabies, both of whom responded well to therapy.

In addition to the skin scrapings, the clinical picture was also diagnostic. One acquires the infection by close contact. Although they never found the original source of the infection, various people worked with the patients, some of whom also worked at other facilities, including a psychiatric hospital; linens and towels can also be involved in transmission. In a situation where an index case is found, other patients with similar symptoms may be treated. The drug of choice is 5% permethrin, applied as a topical cream. A mild steroid cream may also be helpful in sensitive individuals.

Three examples of Sarcoptes scabiei from skin scrapings. The different colors reflect the use of different filters and light microscopy options. It is important to remember that the light should not be too bright; if so, the organisms will appear clear and will not be visible.

This is a tissue slide of Sarcoptes scabiei, the itch mite.

Usual skin sites are the interdigital spaces, backs of the hands, elbows, axillae, groin, breasts, umbilicus, penis, shoulder blades, small of the back, and buttocks. The outstanding clinical symptom is intense itching. Scratching commonly causes weeping, bleeding, and sometimes secondary infection. A form of the infestation called Norwegian scabies can occur in immunosuppressed or anergic individuals; many mites are present in keratotic excrescences on the body and extremities, but pruritus is usually absent. Such individuals will harbor thousands of mites compared to the normal case with no more than a dozen or two at any given time. Scabies is highly contagious and has been reported as the cause of hospital epidemics. Specific recovery techniques are listed below.

Skin Scraping Technique

Diagnosis can be confirmed by demonstration of the mites, eggs, or scybala (fecal pellets). Because the mites are located under the surface of the skin, scrapings must be made from the infected area.

  1. Place a drop of mineral oil on a sterile scalpel blade. (Mineral oil is preferred over potassium hydroxide solution or water. Mites will adhere to the oil, skin scales will mix with mineral oil, refractility of differences will be greater between mite and oil, and oil will not dissolve fecal pellets.)
  2. Allow some of oil to flow onto the papule.
  3. Scrape vigorously six or seven times to remove the top of the papule. (There should be tiny flecks of blood in the oil.)
  4. Transfer the oil and scraped material to a glass slide (can use an applicator stick).
  5. Add 1 or 2 extra drops of mineral oil to the slide, and stir the mixture. Any large clumps can be crushed to expose hidden mites.
  6. Place a coverslip on the slide and examine (first on low power). The adult mites range from approximately 215 to 390 microns in length, depending on sex. The eggs are 170 microns long by 92 microns wide, and the fecal pellets are about 30 by 15 microns. The fecal pellets will be yellow-brown.

Plastic Box or Petri Dish Method

If mineral oil preparations of skin scrapings fail to demonstrate the mites, the encrusted skin scrapings, etc., can be placed in a small plastic box or small petri dish. The container should be left undisturbed at room temperature for 12 to 24 h. Away from the living host, the mites will drop down onto the bottom of the box or dish and can be seen with a magnifying glass or with a dissecting microscope.

References:

  1. Garcia, LS, 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, DC.
  2. Garcia, L.S. 2009. Practical Guide to Diagnostic Parasitology, 2nd Ed., ASM Press, Washington, D.C.