A standardized skin-surface biopsy (1 cm2) of the check was performed in 49 patients with rosacea [13 with erythemato-telangiectatic rosacea (ETR), three with squamous rosacea (SR), 33 with papulopustular rosacea (PPR)], and 45 controls. A mean density of 0.7 Demodex folliculorum/cm2 was found in controls, 98% of whom had less than five Demodex/cm2. When all clinical types of rosacea were considered collectively, the density of Demodex was significantly higher in patients with rosacea than in controls (mean = 10.8/cm2; P < 0.001). When the various clinical types of rosacea were considered separately, Demodex density was statistically significantly higher than in controls only in the PPR patients (mean = 12.8/cm2; P < 0.001). The same type of comparison was also made for three other groups of subjects--patients with isolated inflammatory papules (n = 4), rhinophyma (n = 3), and HIV infection (n = 21), respectively: in these groups, the Demodex density did not differ significantly from controls. The present study demonstrates a high density of D. folliculorum in PPR, and supports its pathogenic role in the papulopustular phase of rosacea. The study suggests that standardized surface biopsy could be a useful diagnostic tool for PPR, with a 98% specificity when Demodex density is higher than 5/cm2.

No abstract

Papulopustular rosacea (PPR) is a common facial skin disease, characterized by erythema, telangiectasia, papules and pustules. Its physiopathology is still being discussed, but recently several molecular features of its inflammatory process have been identified: an overproduction of Toll-Like receptors 2, of a serine protease, and of abnormal forms of cathelicidin. The two factors which stimulate the Toll-like receptors to induce cathelicidin expression are skin infection and cutaneous barrier disruption: these two conditions are, at least theoretically, fulfilled by Demodex, which is present in high density in PPR and creates epithelial breaches by eating cells. So, the major pathogenic mechanisms of Demodex and its role in PPR are reviewed here in the context of these recent discoveries. In this review, the inflammatory process of PPR appears to be a consequence of the proliferation of Demodex, and strongly supports the hypothesis that: (1) in the first stage a specific (innate or acquired) immune defect against Demodex allows the proliferation of the mite; (2) in the second stage, probably when some mites penetrate into the dermis, the immune system is suddenly stimulated and gives rise to an exaggerated immune response against the Demodex, resulting in the papules and the pustules of the rosacea. In this context, it would be very interesting to study the immune molecular features of this first stage, named "pityriasis folliculorum", where the Demodex proliferate profusely with no, or a low immune reaction from the host: this entity appears to be a missing link in the understanding of rosacea.

Diagnosing papulopustular rosacea is not always straightforward; no specific diagnostic test is currently available. A high density of Demodex mites is consistently observed in this condition. This retrospective study assesses an improved method for evaluating Demodex density among 1,044 patients presenting to our dermatology practice. The skin was cleaned with ether and Demodex densities were measured in 2 consecutive standardized skin surface biopsies taken from the same site. Mean densities in patients with rosacea and demodicosis were much higher than those in healthy controls and patients with other facial dermatoses. The optimal cut-off values for the 2 biopsies were combined and the resultant criterion (presence of a first biopsy density < 5 Demodex/cm2 or a second biopsy density < 10 Demodex/cm2) enabled confirmation of a diagnosis of rosacea or demodicosis with a sensitivity of 98.7% and specificity of 95.5%, making this a valuable diagnostic tool for dermatologists in routine clinical practice.

A standardized skin surface biopsy was performed in 34 patients suffering from skin diseases with high Demodex folliculorum density (Dd) > 5D/cm2 before, during and after topical treatment. The patients were randomized into six comparable groups to study six topical treatments: metronidazole 2%, permethrin 1%, sublimed sulphur 10%, lindane 1%, crotamiton 10% and benzyl benzoate (BB) 10%. Their acaricidal activity was measured according to three criteria: (i) for each treatment, decrease of Dd to under the normal threshold (< or = 5 D/cm2); (ii) for each treatment, a significant decrease in Dd; and (iii) comparison of the relative difference in Dd between treatments. These three criteria converged to establish the acaricidal activity of BB on D. folliculorum; the efficacy of crotamiton was demonstrated by the second criterion. An important irritating effect was observed with BB and sulphur.