A new superficial needle-scraping method for assessing Demodex density in papulopustular rosacea

Standardized skin surface biopsy (SSSB) is often performed to determine the density of Demodex mites in facial papulopustular eruptions.

We aimed to test the applicability of a new, "superficial needle-scraping" (SNS) method for assessing Demodex density in papulopustular rosacea (PPR).

Using SNS method, we measured the Demodex density in patients with PPR, also enrolling the patients with acne vulgaris as controls. SNS was performed by gently scraping off 5 small pustules with the convex surface of the tip of an 18# needle for examination. For comparison, SSSB was also performed in patients with PPR. Demodex density was expressed as "mites per 5 pustules" for SNS and as "mites per cm² " for SSSB.

A total of 40 patients with PPR and 35 patients with acne vulgaris were recruited. There were no statistically significant differences in age or sex between the PPR and acne groups. The Demodex density was 5.6 ± 4.2 in the PPR group versus 0.3 ± 1.0 in the acne group (P < .001). The cutoff of "≥3 Demodex mites per 5 pustules" gave a sensitivity of 78% and a specificity of 97%, and the area under the receiver operating characteristic curve was 0.89. Moreover, SNS and SSSB gave mutually concordant results (positive or negative) in half of the patients.

Our study suggests that SNS is a simple and convenient method for assessing Demodex density of pustules in PPR and can be a useful alternative or addition to SSSB for evaluation of Demodex-associated facial papulopustular eruptions.