๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
Demodicosis
Demodicosis
There are two species of Demodex that live in a symbiotic relationship in human hair follicles. The mites are D. folliculorum and D. brevis. The former is mainly found in the infundibulum of the hairs and the latter in the sebaceous glands. They are ubiquitous in the skin but there is a predilection for the face. Their pathogenetic role in skin diseases has always been controversial and they are often regarded as innocent bystanders. However, it does seem that in a small number of cases, particularly in immunocompromised patients, they have an important role in causation of disease.1โ4 The mites do not appear to be a primary factor in the development of rosacea although they may play a part in the granulomatous form of the disease. Traditionally, three facial forms of involvement have been described: pityriasis folliculorum, rosacea-like demodicosis, and demodicosis gravis. Recently, a classification of the disease into primary and secondary forms has been proposed. The latter is associated with immunosuppression. The primary form has been divided into: 1. spinulate demodicosis or pityriasis folliculorum not usually associated with inflammation; 2. papulopustular/nodulocystic or conglobate demodicosis presenting with inflamed lesions with predilection for skin around the eyes and mouth; 3. ocular demodicosis; and 4. auricular demodicosis.5 Skin eruptions attributed to the mites have variable manifestations and include a rosacea-like eruption, a perioral dermatitis-like eruption, follicular plugging, and erythema, and a disseminated form in immunocompromised patients.1โ13 Localized pustules and even abscesses have also been reported.14 An unusual case of a patient with demodicosis presenting as a facial plaque after ophthalmic herpes zoster has been described. In a further case, the disease mimicked favus in a child.15 Eye involvement usually presents with chronic blepharitis or chalazion and more rarely with keratoconjunctivitis. Ear involvement is mainly associated with otitis externa or myringitis. Adults are mainly affected but cases in children have been reported.10โ12,16
Pathogenesis and histologic features The pathogenesis of periorificial dermatitis is not clearly understood, but the condition seems to be etiologically linked in some cases to the use of potent topical steroids, the application of cosmetics, certain toothpastes, epoxy diacrylates in dental composite resins, contraceptive pills, some moisturizing creams, and propolis.17โ27 In rare patients, the disease appears during pregnancy and may flare up before the menstrual period.27,28 Even inhaled and systemic corticosteroids have triggered perioral dermatitis.29โ31 Physical sunscreens with high sun protection factor have also been blamed for causing the disease in children.32 Multiple dental fillings with a mercury-containing amalgam induced perioral dermatitis in a girl, and in a further case the disease appears to have been triggered by orthognathic surgery.33,34 An association has also been reported in renal transplant patients on systemic steroids and azathioprine.35 Fusobacteria have also been suggested as having a possible role in the disease.36
Pathogenesis and histologic features The pathogenetic link between the mites and cutaneous disease is a matter of controversy. In cases where there seems to be a clear link, the density of mites is very high.4 A role for the symbiotic relationship between the mites and bacteria has been suggested but remains to be proven.
Biopsy shows mild acanthosis, focal spongiosis, and hyperkeratosis with parakeratosis and a mild perivascular and periadnexal lymphohistiocytic infiltrate. The appearances are almost indistinguishable from those found in rosacea.37 Ruptured hair follicles with microabscess formation are occasionally seen. Sometimes granulomata with sarcoidal features are present.38
Histologically, the findings combine suppurative and granulomatous changes. Dilated hair follicles with multiple mites are seen and there is formation of neutrophilic pustules. This is associated with a variable, perifollicular mononuclear cell infiltrate composed of lymphocytes and plasma cells. When the hair follicle ruptures, focal granulomata are seen and often contain fragments of the mites.