Biopsy for this patient revealed folliculitis with Demodex mites visualized on histology. Direct immunofluorescence was negative. A KOH preparation was performed and was positive for large numbers of Demodex. Bacterial cultures were negative. The patient was started on a course of submicrobial doxycycline and ivermectin and showed marked improvement 1 month following treatment.
Demodex folliculorum and Demodex brevis (collectively referred to as Demodex) are microscopic parasitic mites that commonly live on human skin.1 Typically, the mite remains asymptomatic. However, in higher numbers, the infestation may cause dermatoses, called demodicosis. Lesions often present as itchy papules, pustules, and erythematous scaling on the face, ears, and scalp. Blepharitis may be present. Demodex folliculitis is more common in immunocompromised patients.2
Demodex may have a causative role in rosacea and present similarly, with a key difference being that Demodex-type rosacea is more scaly/dry and pustular than common rosacea.1 In Demodex folliculitis, bacterial cultures are often negative. A skin scraping for KOH will reveal increased mite colonization. The Demodex mite may also be seen in histologic slides.
Treatment of Demodex folliculitis includes crotamiton cream, permethrin cream, oral tetracyclines, topical or systemic metronidazole, and topical or oral ivermectin.
This case and photos were submitted by Susannah McClain, MD, Three Rivers Dermatology, Pittsburgh.
References
1. Rather PA and Hassan I. Indian J Dermatol. 2014 Jan;59(1):60-6.
2. Bachmeyer C and Moreno-Sabater A. CMAJ. 2017 Jun 26;189(25):E865.