Demodicidosis
For several months, a 43-year-old woman had erythematous plaques on the cheeks that were more prominent on the right side. The patient had no pruritus but reported occasional facial burning. She had tried over-the-counter lotions but no medicated or corticosteroid topical preparations. She was otherwise healthy and was currently taking no medications.
The rash had overlying scale and minimal papules (A). No pustules were noted. Skin scrapings stained with chlorazol black E revealed transparent mites, 0.3 to 0.4 mm in length, with 8 segmented legs (B). Some areas of colonization had as many as 13 mites per visual field. Demodicidosis was diagnosed on the basis of the clinical presentation and microscopic evaluation.
About 65 species of the Demodex mites exist. Currently, only 2 of these species infest human skin: Demodex folliculorum is a metazoan commonly found to parasitize the lumen of hair follicles, while Demodex brevis infests the pilosebaceous glands.1,2 The Demodex mite belongs to the Arachnida class and has been associated with several skin disorders, including pityriasis folliculorum, rosacea-like demodicidosis, and demodicidosis gravis. Men and women are affected equally, and the incidence increases with age.3
The mites are most active at night. Their life span ranges from 18 to 24 days.4 Although many authors disagree about whether the mite is found in a small percentage of or in all humans, it is clear that its presence is not always pathological. 5 We consider more than 5 mites per visual field to be diagnostic of demodicidosis.
Patients with demodicidosis often present with erythematous papules and pustules with an underlying erythema on the forehead, cheeks, and nose. Madarosis (loss of eyelashes) can occur with significant infestation. The Demodex mite causes intercellular edema of the hair shaft and thus loss of hair resiliency.6 There is no single accepted treatment for demodicidosis. Topically, it has been treated with 5% permethrin cream, benzyl benzoate, lindane, and crotamiton.7 Oral ivermectin (200 μg/kg) has been found to have some efficacy in eradicating the mite.2 This patient’s symptoms resolved after treatment with 1 dose of ivermectin (6 mg).
1. Düzgün OY. Comparison of Demodex folliculorum density in haemodialysis patients with a control group. J Eur Acad Dermatol Venereol. 2007;21:480-483.
2. Bolognia JL, Jorizzo JL, Rapini RP. Dermatology. London: Elsevier; 2003:509, 519.
3. Nutting WB. Hair follicle mites (Acari: Demodicidae) of man. Int J Dermatol. 1976;15:79-98.
4. Rufli T, Mumcuoglu Y. The hair follicle mites Demodex folliculorum and Demodex brevis: biology and medical importance. A review. Dermatologica. 1981;162:1-11.
5. Norn MS. Demodex folliculorum: incidence, regional distribution, pathogenicity. Dan Med Bull. 1971;18:14-17.
6. English FP, Nutting WB. Demodicosis of ophthalmic concern. Am J Ophthalmol. 1981;91:362-372.
7. Thiboutot DM, Strauss JS. Diseases of the sebaceous glands. In: Freedberg IM, Eisen AZ, Wolff K, et al, eds. Fitzpatrick’s Dermatology in General Medicine. New York: McGraw-Hill; 2003: 693-695.