A clinico-pathological approach to the classification of human demodicosis

Demodicosis is a parasitic skin disease caused by the follicle mites Demodex folliculorum and Demodex brevis. Although there are several clinical variants of this disease, a clear classification is missing.

To characterize the clinical features and course of the different forms of demodicosis.

Prospective study of 87 patients with clinical symptoms of demodicosis and positive acarological findings. Each patient was examined an average of six times during the treatment period.

We suggest that demodicosis be divided into both primary and secondary types. The usual etiological agent of primary demodicosis is D. folliculorum, which causes an erythemato-squamous eruption in the facial T-zone. The rash starts on unaltered skin and covers 8 - 15 % of the face. Pruritus accompanies the onset of the rash, while erythema is first apparent after papulo-pustules are seen and disappears after treatment. Half the patients show seasonal exacerbations. Secondary demodicosis is usually caused by D. brevis and characterized by a symmetrical malar papulo-pustular eruption. It develops on diseased skin and covers 30 - 40 % of the face. Pruritus starts after the lesion exacerbation, but erythema precedes the papulo-pustular phase and persists after treatment. Most patients flare during the summer. The facial distribution, seasonality and pathogenesis, as well as the species of mite involved, must be taken into consideration in separating the various forms of demodicosis.