Demodicosis: A clinicopathological study

Background Demodex mites are common commensal organisms of the pilosebaceous unit in human beings and have been implicated in pityriasis folliculorum, rosacea-like demodicosis, and demodicosis gravis. Objective We sought to describe the spectrum of clinicopathological findings and therapeutic responses of demodicosis in Taiwanese patients. Methods We conducted a retrospective study to review clinicopathologic findings and therapeutic responses of 34 cases of diagnosed demodicosis. Results Fifteen cases with positive results of potassium hydroxide examination, standardized skin surface biopsy specimen, and/or skin biopsy specimen, and resolution of skin lesions after anti- Demodex treatment were included for final analysis. Nineteen cases were excluded because of insufficient positive data to make a definite diagnosis. There were 4 male and 11 female patients (age 1-64 years, mean age 38.7 years). The disease was recurrent or chronic with a duration ranging from 2 months to 5 years (mean 15.7 months). The skin lesions were acne rosacea-like (n = 8), perioral dermatitis-like (n = 5), granulomatous rosacea-like (n = 1), and pityriasis folliculorum (n = 1). Skin biopsy was performed in 7 patients. Overall, the histopathology was characterized by: (1) dense perivascular and perifollicular lymphohistiocytic infiltrates, often with abundant neutrophils and occasionally with multinucleated histiocytes; (2) excessive Demodex mites in follicular infundibula; and (3) infundibular pustules containing mites or mites in perifollicular inflammatory infiltrate. The skin lesions resolved after treatment including systemic metronidazole, topical metronidazole, crotamiton, or gamma benzene hexachloride. Limitations Small sample size and a fraction of patients without long-term follow-up are limitations. Conclusion Demodicosis should be considered in the differential diagnosis of recurrent or recalcitrant rosacea-like, granulomatous rosacea-like, and perioral dermatitis-like eruptions of the face. Potassium hydroxide examination, standardized skin surface biopsy, skin biopsy, or a combination of these are essential to establish the diagnosis.