Folliculitis is a common complaint seen in dermatology practice. The differential diagnosis of folliculitis is broad and includes Demodex folliculitis. In humans, the Demodex mite species Demodex folliculorum and Demodex brevis have been found to inhabit the pilosebaceous unit. D folliculorum typically is found in the follicular infundibulum; D brevis exists in the sebaceous and meibomian glands.1 Although the prevalence of Demodex approaches 100% in middle-aged and elderly adults,1 mite density normally is low in healthy skin.2Demodex mites are considered pathogenic only when they are found in large numbers or in an intradermal location3; therefore, it has been suggested that D folliculorum may play a role in various papular and pustular eruptions of the head and neck, such as demodicosis and rosacea.3 We examine a case of scalp folliculitis secondary to Demodex infection and the role that this organism plays in the pathogenesis of folliculitis, as well as the available treatment options.
A 57-year-old white man presented to our department in June 2004 with an "infected scalp" and scalp irritation for 2 months. The patient was diagnosed with bacterial folliculitis and treated with clindamycin 1% gel twice daily for 1 month. He presented for follow-up in July 2004 with continued complaint of scalp pruritus and rash (Figure 1). Results of an examination showed a deep pink 10X7-cm plaque on the scalp with hyperkeratosis and pustules. An ectoparasite wet mount prepared from one of the pustules revealed the presence of several Demodex mites (Figure 2). The patient was treated with sulfacetamide 10% plus sulfur 5% cream twice daily, in addition to a 2-week course of selenium sulfide 2.5% shampoo once daily. When the patient was seen for follow-up in September 2004, his entire scalp had cleared (Figure 3). He was instructed to continue the selenium sulfide 2.5% shampoo twice weekly for 6 months to prevent recurrence.
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The Demodex mite is a ubiquitous arthropod measuring approximately 0.1 to 0.4 mm in length. Typically, it infests areas around the eyelids, nose, and ear canals in human hosts.4 The life cycle of the mite is 18 to 24 days. The female mite lays 20 to 24 eggs in a hair follicle where the eggs are nourished by the surrounding pilosebaceous unit. The eggs hatch and the nymphs continue to live in the follicle where their main source of food is human glandular secretions.5 The mite primarily is an asymptomatic inhabitant of human pilosebaceous follicles and poses no harm to the host.1
The role of D folliculorum in cutaneous disease in humans remains controversial. The pathogenicity is difficult to establish secondary to the localization of the disease, the widespread prevalence of infection with the D folliculorum mite, and the obligate nature of the parasite; therefore, the detection of the presence of the mite is not, in and of itself, enough evidence to establish pathogenicity.6 Results of immunohistochemical staining have shown that helper T lymphocytes predominate in the dermal infiltrate of demodicosis suggesting a possible role of cell-mediated immune response and delayed hypersensitivity.7 There also is evidence for a humoral immune response component with increased macrophages and Langerhans cells in the presence of infestation with Demodex.7
Demodex mites have been implicated as a causative agent in rosacea and pustular folliculitis.6 It is important to consider the possibility that the vascular changes of rosacea create an environment that is favorable to the multiplication of Demodex mites and their penetration into the dermis.8 Forton and Seys6 reported that Demodex mites are associated with the inflammatory symptoms of rosacea and that the mites are present in greater numbers and higher frequencies in patients with rosacea. Additionally, a study by Georgala et al7 evaluated the importance of D folliculorum in the etiology and course of rosacea and showed that D folliculorum was found in 83 (90.2%) of 92 rosacea subjects studied but in only 11 (11.9%) of the 92 controls, thereby concluding that although Demodex mites may not be the cause of rosacea, they may represent an important cofactor. Finally, Vollmer9 examined 388 follicles in 24 resections of skin for the presence of histologic folliculitis and Demodex mites. Results showed that Demodex mites were found in 87 (42%) of 208 follicles with inflammation but in just 18 (10%) of 180 follicles without inflammation. Furthermore, 87 (83%) of 105 follicles with Demodex showed inflammation, which demonstrated a nonrandom association between these 2 entities.9 A study by Meinking et al10 supported the rapid clearing of papulopustular dermatosis of the scalp and granulomatous rosacea when treated with scabicidal preparations such as permethrin or ivermectin, thereby supporting the pathogenic role of Demodex in papulopustular eruptions.