2.4.6 Demodicosis

Most infections are caused when demodex mites are overpopulating, penetrating the follicular wall or wall of the sebaceous duct, colonizing the follicular opening and interfollicular epidermal surface. Two types have to be differentiated: Demodex folliculorum and Demodex brevis. They have eight legs. Larva stage takes 7 days, adult life time around two to three weeks. Whereas D. brevis (0.15-0.2 mm) is mostly found in the follicles of the eye lashes, D. folliculorum (0.2-0.4 mm) is found in the sebaceous follicles. Usually, the mites are not found in infants. Aged skin with wider follicular openings predisposes the growth. Other predisposing factors include aged skin with actinic elastosis, immunodeficiency such as HIV infection or under chemotherapy, alcoholism and diabetes.

In rosacea it is an important factor in driving the inflammatory course and leading to granulomatous courses because mites invade the sebaceous duct which ruptures and they enter the papillary and deeper dermis. Demodex mites harbour Bacillus oleronius which may contribute to additional inflammation.

Demodex mites move in the night 8-16mm /h over the skin, deposit eggs and can produce itch and tickling. Light makes them move back to the follicle to hide. Skin feels sensitive and sometimes more scaly, may produce tiny rough feeling by striking over the surface (spinula like pattern) and shows some redness. Rarely an eczematous pattern is observed. The appearance of papules and pustules mimic an acneiform feature. The lesions are mostly not symmetrically located. Sometimes small abscesses develop. In particular, the eye lashes are prone to have strong irritating feeling when blinking and hordeolum like lesions can appear. Severe conjunctivitis and loss of eye lashes can follow. At the external ear canal an increased scaling and itching is recognized.

Dermatoscopy can make the spinula visible. A cyanoacrylate tape stripe can help to visualize the mites under the microscope and numbers can be counted for therapy success (in clinical trials).

Not necessary for a normal diagnosis, but in granulomatous diseases of the face and in rosacea recommended. The mites are in masses populating the follicular canal with folliculitis and perifolliculitis. In case of penetrating the wall, foreign body reaction appears in the dermis.

• seborrhoic dermatitis

• periorificial dermatitis

• acne

• folliculitis

• superficial granulomatous sarcoidosis

Others: follicular T-cell-lymphoma, spinula follicular pattern in plasmocytoma, P-type of atopic dermatitis, tinea follicularis and candida.

Prevention: regular use of facial cleansers, avoiding UV light as promoter of actinic elastosis. Hands off from the face. In immunodeficient status an accompanying application of permethrin / ivermectin cream can be considered.

Therapy: Topical treatment is the mainstay. Life span with production of new larvae has to be considered. Weekly application of 5% permethrin ointment including antiseptics in case of papulo-pustular pattern over 4 weeks. Other options are 1.0% ivermectin creme daily long-term. In granulomatous and absceding courses an oral ivermectin treatment is necessary. In rosacea with demodex provocation ivermectin crème 1% long-term is essential.