Human Demodicosis: Revisit and a Proposed Classification

W. Chen; G. Plewig

Disclosures

The British Journal of Dermatology. 2014;170(6):1219-1225. 

In This Article

Definition and Diagnosis

Human demodicosis is a skin disease of the pilosebaceous units associated with human Demodex mites that involves predominantly the face and head.[3] Two clinical variants, primary and secondary, can be observed. Primary demodicosis can be defined when the following diagnostic criteria are met: (i) absence of pre-existing or concurrent inflammatory dermatoses, such as acne, rosacea or perioral dermatitis; (ii) abnormal increase in mite colonization, which should be identified from the active lesions at the time of examination; and (iii) remission of the disease only after adequate treatment with topical or systemic acaricides/arachnicides,[3,6] but not with antibiotics possessing anti-inflammatory effects, such as tetracycline or doxycycline, or macrolides (erythromycin/azithromycin/clarithromycin). A count of more than 5 mites per cm2 identified from lesions by way of 'standardized skin surface biopsy' is currently accepted as abnormal, although this figure is based on very limited studies.[7] Moreover, considering that the method of sampling and quantification varies in most case reports and that control groups are often lacking, it is unclear whether this threshold of mite density can be applied to characterize a diseased state in different age groups and different sexes.[8] It is also unknown whether Demodex mites captured by 'standardized skin surface biopsy' from their sequestration in the deep follicular canal are of clinical relevance in the initiation of inflammation. Preliminary studies using new diagnostic techniques such as dematoscopy,[9] confocal laser scanning microscopy[10] or high-definition optical coherence tomography show promising results;[11] however, the precision, validity and clinical practicability of these methods remain to be determined. An integration of imaging studies and fluorescein staining may provide a fast and exact solution for the detection and (semi)quantification of mites in daily clinical practice.[12]

Skin lesions associated with an abnormal increase of Demodex mites in patients with other known skin or systemic diseases can be classified as secondary demodicosis. It occurs most commonly in significantly immunosuppressed patients, such as those with leukaemia and HIV infection,[13–16] as well as those being treated with immunosuppressants including topical glucocorticoids or topical calcineurin inhibitors.[17,18] Although the relationship is less straightforward, other conditions associated with secondary demodicosis include certain inflammatory dermatoses,[19–22] treatment with epidermal growth factor receptor inhibitors,[23,24] skin tumours,[25–27] chronic renal failure[28] and ultraviolet phototherapy ( Table 1 ).[29] The primary role of Demodex mites in the pathogenesis of rosacea remains debatable, considering that none of the available data show a direct positive causal relationship.[19,30] The hypothesis that primary demodicosis is caused by D. folliculorum and secondary demodicosis by D. brevis has not yet been proven and differs considerably from our concept of classification.[31]

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