Demodex Folliculitis of the Scalp: Clinicopathological Study of an Uncommon Entity.

Demodex is a saprophytic mite in humans commonly present in the pilosebaceous units, which has been implicated as a pathogen in several skin conditions. The clinical presentation and histopathology of Demodex folliculitis of the scalp have been described in only a few case reports. This study was performed to further elucidate the clinicopathological features of this entity. We have studied 333 consecutively submitted scalp biopsies performed for hair loss and alopecia. All specimens were completely step-sectioned. Biopsies with Demodex mites were further studied histopathologically, and the patients' clinical files were reviewed. There were 17 biopsies (5.1%) with Demodex in at least 1 pilosebaceous unit. Based on the clinical presentation, histopathology, and response to therapy, Demodex was considered to be nonpathogenic in 13 cases. The remaining 4 cases were characterized by hair loss, scalp erythema, scales, and pustules. There were 2 or more pilosebaceous units with Demodex along mononuclear and/or neutrophilic infiltrates around and in the involved follicles and occasionally granulomas. All 4 cases responded completely to metronidazole therapy. In conclusion, Demodex is infrequently found in scalp biopsies for hair loss and alopecia, and, in most cases, it does not seem to be pathogenic. Occasionally, however, it is associated with folliculitis characterized by hair loss, erythema, scales, and pustules clinically; neutrophilic and/or mononuclear-cell folliculitis with occasional granulomas histopathologically; and a prompt response to anti-Demodex therapy.