Papulopustular rosacea and rosacea-like demodicosis: two phenotypes of the same disease?

Papulopustular rosacea and rosacea-like demodicosis have numerous similarities, but they are generally considered as two distinct entities, mainly because the causal role of the Demodex mite in the development of rosacea is not yet widely accepted. Several clinical characteristics are traditionally considered to differentiate the two conditions; for example, papulopustular rosacea is typically characterized by central facial papulopustules and persistent erythema, whereas small superficial papulopustules and follicular scales rather suggest rosacea-like demodicosis. However, none of these characteristics is exclusive to either entity.

To explore differences in Demodex densities according to clinical characteristics traditionally associated with these two conditions.

Retrospective, observational, case-control study of 242 patients with central face papulopustules. Demodex densities were measured on two consecutive standardized skin surface biopsies.

In the whole cohort, Demodex densities were greater in patients with persistent erythema than in those without. In 132 patients without recent treatment or other facial dermatoses, 120 (91%) had persistent erythema, 119 (90%) small superficial papulopustules and 124 (94%) follicular scales; 116 (88%) simultaneously had clinical characteristics traditionally associated with both papulopustular rosacea and rosacea-like demodicosis. Higher Demodex densities were linked to the presence of follicular scales, but not to papulopustules size, nor to the presence/absence of persistent erythema.

Our observations highlight the difficulty differentiating between these entities and suggest that rosacea-like demodicosis and papulopustular rosacea should no longer be considered as two separate entities, but rather as two phenotypes of the same disease.