Presentation of Quiz #74

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An 80-year-old male presented to the dermatology clinic with a several week history of scalp scales over the nape, temporal areas and ears.  The patient reported no other symptoms other than mild pruritus.  Skin scrapings were submitted to the microbiology laboratory.  The following images were seen.

  

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Answer and Discussion of Quiz #74
Several genera infect the skin of mammals, with Sarcoptes scabiei being found in humans, although some mange mites of animals occasionally cause a pruritic rash in humans. S. scabiei is microscopic and lives in cutaneous burrows, where the fertilized female deposits eggs. Scabies is transmitted by close contact with infested individuals, including touching, shaking hands, sexual contact, and contact in day care centers with children and the elderly. Scabies is common among those in overcrowded conditions, and has been associated with immigrants, poor hygiene, poor nutritional status, homelessness, dementia and sexual contact.The usual skin sites that are susceptible to infection are the interdigital spaces, backs of the hands, elbows, axillae, groin, breasts, umbilicus, penis, shoulder blades, small of the back, and buttocks. In this particular case, the scalp was also involved. The outstanding clinical symptom is intense itching. Scratching commonly causes weeping, bleeding, and sometimes leads to secondary infection.

A form of the infestation, called crusted 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. This infestation is highly contagious and has been reported to be the cause of hospital epidemics. Scabies occurs worldwide, with at least 300 million cases each year.

Crusted scabies usually occurs in individuals with underlying immunosuppressive diseases, including human immunodeficiency virus infection, human T-cell lymphotropic virus 1 infection, and leukemia, but has also been seen in healthy patients. Clinically, crusted scabies presents as dermatitis with an erythematous scaly eruption on the face, neck, scalp, and trunk.  However, the plaques of crusted scabies can sometimes be misdiagnosed as psoriasis, eczema, Darier’s disease, contact dermatitis, ichthyosis, or an adverse drug reaction.

Diagnosis
The 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 (see image above).

1. Place a drop of mineral oil on a sterile scalpel blade. (Mineral oil is preferred to potassium hydroxide solution or water. Mites adhere to the oil, skin scales mix with the oil, the refractility differences are greater between the mite and the oil, and the oil does not dissolve fecal pellets.)

2. Allow some of the 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 (an applicator stick can be used).

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 µm in length, depending on sex. The eggs are 170 µm long by 92 µm wide, and the fecal pellets are about 30 by 15 µm. The fecal pellets are yellow-brown.

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 drop to the bottom of the box or dish and can be seen with a magnifying glass or dissecting microscope.

Discussion
The patient was treated with oral ivermectin and 5% topical permethrin; crust and scale removal was required for the scabicides to penetrate.  The hyperkeratotic plaques resolved approximately 2 weeks later.

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