A standardized skin-surface biopsy (1 cm2) of the cheek was performed in 49 patients with rosacea [13 with erythematotelangiectatic 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.