Atlas of pathophysiology, 2 Edition

Part II - Disorders

Skin Disorders

Atopic dermatitis

Atopic (allergic) dermatitis (also called atopic or infantile eczema) is a chronic or recurrent inflammatory response commonly associated with other atopic diseases, such as bronchial asthma and allergic rhinitis.

Age Alert

Atopic dermatitis commonly develops in infants and toddlers between ages 1 month and 1 year, usually in those with a strong family history of atopic disease. These children commonly develop other atopic disorders as they grow older.

Typically, this form of dermatitis flares and subsides repeatedly before finally resolving during adolescence, but it can persist into adulthood.

Causes

Exact etiology unknown; genetic predisposition likely

Possible contributing factors

·   Food allergy, especially eggs, peanuts, milk, or wheat

·   Infection

·   Chemical irritants

·   Extremes of temperature and humidity

·   Psychological stress or strong emotions

Pathophysiology

The allergic mechanism of hypersensitivity results in a release of inflammatory mediators through sensitized antibodies of the immunoglobulin (Ig) E class. Histamine and other cytokines induce acute inflammation. Abnormally dry skin and a decreased threshold for itching set up the “itch-scratch-itch” cycle, which eventually causes lesions (excoriations, lichenification).

Signs and symptoms

·   Erythematous areas on excessively dry skin; in children, typically on the forehead, cheeks, and extensor surfaces of the arms and legs; in adults, at flexion points (antecubital fossa, popliteal area, and neck)

·   Edema, crusting, scaling caused by pruritus and scratching

·   Multiple areas of dry, scaly skin, with white dermatographism, blanching, and lichenification with chronic atrophic lesions

·   Infantile form presents as red skin with tiny vesicles, especially on the face (sparing the mouth); possible development of wet crusts and fissures

·   In blacks, follicular eczema common, appearing as discrete follicular papules involving hair follicles in the affected area

·   Pinkish, swollen upper eyelid and double fold under lower lid

·   Viral, fungal, or bacterial infections and ocular disorders possible secondary conditions

Diagnostic test results

Blood tests reveal eosinophilia and elevated IgE levels.

Treatment

·   Eliminating allergens and avoiding irritants (strong soaps, cleansers, and other chemicals), extreme temperature changes, and other precipitating factors

·   Preventing excessive dryness of the skin (critical to successful therapy) by maintaining adequate fluid intake, taking tepid baths, and humidifying air

·   Topical tar preparations in a lubricating base (contraindicated for intensely inflamed or open lesions)

·   Topical corticosteroid ointment, especially after bathing, to alleviate inflammation; moisturizing cream between steroid doses to help retain moisture

·   Topical doxepin hydrochloride

·   Topical immunomodulators, such as tacrolimus and pimecrolimus

·   Systemic antihistamines such as diphenhydramine

·   Systemic corticosteroid therapy for severe disease only

·   Ultraviolet B or psoratens plus ultraviolet A therapy

·   In severe adult-onset disease, cyclosporine A, if other treatments fail

·   Antibiotics, if skin culture positive for bacteria

P.375

APPEARANCE OF ATOPIC DERMATITIS

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Clinical Tip

Morgan's line

In children with atopic dermatitis, severe pruritus with recurrent rubbing leads to characteristic pink pigmentation and swelling of the upper eyelid and a double fold under the lower lid (Morgan's line, Dennie's sign, or mongolian fold).

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