Demodicosis

Synonyms

Pityriasis folliculorum.

Epidemiology

Around 90 % of the world population have some demodex mites on the body surface, but around 5 to 10 % only suffer from a demodex infection.

Definition

Demodex mites are living in the follicular canal of the skin. In case of an infectious course with inflammation and a high density of demodex mites (> 5/cm²) it is called Demodicosis.

Aetiology & Pathogenesis

Most infections are caused when demodex mites are overpopulating, penetrating the follicular wall, colonizing the follicular opening and interfollicular epidermal surface. Two types have to be differentiated:

Demodex folliculorum ( 0.2-0.4 mm), mostly in sebaceous follicles.
Demodex brevis (0.15-0.2 mm), mostly found in the follicles of the eye lashes.

Predisposing factors: aged skin (wider follicular openings), actinic elastosis, immunodeficiency (HIV) or chemotherapy, alcoholism and diabetes, rosacea

Signs & Symptoms

Demodex mites move in the night 8-16mm /h over the skin, deposit eggs and can produce itching. Light makes them moving 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. The appearance of papules and pustules mimick an acneiform feature. Sometimes small abcesses and granulomatous reactions may develop. In particular the eye lashes are prone to involvement.

Localisation

Demodex mites are preferentially found on the facial skin; not symmetrical. The forehead with high density of sebaceous gland follicles are predisposed followed by the nose cheeks ,chin, eye lashes and outer ear canal. In males with long standing alopecia demodex mites are also found on the naked scalp.

Classification

Primary demodicosis (sui generis): due to abnormal increase in mite colonization.

Demodex folliculorum ( spinulate demodicosis or pityriasis folliculorum).
papulopustular/nodulocystic or conglobate demodicosis.
ocular demodicosis.

Secondary demodicosis: due to immunosuppression or presence of pre-existing or concurrent inflammatory dermatoses (acne, rosacea perioral dermatitis)

Laboratory & other workups

Dermatoscope can make the spinula visible. A cyanoacrylate tape stripe can help to visualize the mites under the microscope.

Dermatopathology

Not necessary. The mites are in masses populating the follicular canal with folliculitis and perifolliculitis, sometimes granulomatous reactions.

Course

Chronic or recurs frequently.

Complications

Scratching with secondary infection with other microbes. Furuncle. Severe conjunctivitis and loss of eye lashes can occur. Increased scaling and itching at the external ear canal.

Diagnosis

Clinical picture, dermatoscopy, KOH preparation, cyanoacrylate stripe.

Differential diagnosis

Seborrhoeic dermatitis, periorificial dermatitis, acne, folliculitis.

Others: follicular T-cell-lymphoma, spinula follicular pattern in plasmacytoma (Nazzaro), atopic dermatitis, tinea follicularis and candida.

Prevention & Therapy

Prevention : regular use of facial cleansers ,avoiding UV light (promoter of actinic elastosis).

Topical: 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 longterm.

In granulomatous and absceding courses: oral ivermectin treatment is necessary.

Special

None.

2.4.6 Demodicosis