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.
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