Erythematotelangiectatic rosacea may be associated with a subclinical stage of demodicosis: a case–control study

Summary Background Facial densities of Demodex mites have been observed to be greater in patients with demodicosis and papulopustular rosacea than in healthy control patients. In patients with erythematotelangiectatic rosacea (ETR), this density has been observed to be similar to or greater than that of healthy controls. Erythema and telangiectasia, characteristics of ETR, are often observed among patients with pityriasis folliculorum, a discreet demodicosis, suggesting a possible link between these conditions. Objectives To compare the facial Demodex densities of patients with clinical ETR and patients with healthy skin, demodicosis, rosacea with papulopustules, and other facial dermatoses. Methods In this retrospective study, we recorded Demodex densities measured using two consecutive standardized skin surface biopsies (SSSB1 and SSSB2) in 23 patients with ETR, 20 healthy control patients, 590 patients with demodicosis, 254 with rosacea with papulopustules and 180 with other facial dermatoses. Results Patients with ETR had higher Demodex densities (D cm−2) than did the healthy controls (mean ± SEM; SSSB1: 15·7 ± 6·3 vs. 1·8 ± 1·1 D cm−2, P = 0·042; SSSB2: 38·0 ± 13·7 vs. 5·1 ± 2·1 D cm−2, P = 0·026) and patients with other dermatoses (SSSB1: 0·4 ± 0·1 D cm−2, P = 0·004; SSSB2: 1·3 ± 0·3 D cm−2, P = 0·004), but lower densities than patients with demodicosis (SSSB1: 82·7 ± 4·2 D cm−2, P = 0·008; SSSB2: 172·2 ± 7·7 D cm−2, P = 0·001) or rosacea with papulopustules (SSSB1: 86·6 ± 7·3 D cm−2, P = 0·027; SSSB2: 197·0 ± 12·1 D cm−2, P = 0·002). Conclusions ETR may be associated with nonvisible Demodex proliferation, possibly corresponding to a subclinical stage of demodicosis. Dermatologists should be aware of this potential association and look for subclinical demodicosis in patients with ETR, so that topical acaricidal treatment can be offered if Demodex density is high. What's already known about this topic? The facial skin density of Demodex mites in patients with papulopustular rosacea and demodicosis (a skin condition caused by Demodex) is greater than that in healthy control patients. In patients with erythematotelangiectatic rosacea (ETR), facial Demodex density has been observed to be similar to or greater than that of healthy controls. Erythema and telangiectasia, characteristics of ETR, are often observed among patients with pityriasis folliculorum, a discreet demodicosis. What does this study add? Patients with ETR had higher mean Demodex densities