The editors and current author would like to thank and acknowledge the significant contribution of the previous author of this chapter from the 2004 first edition, Dr. M. Stanton Michels. This current second edition chapter is a revision and update of the original author's work

A 2 year-old boy presents with recurrent rashes since soon after he was born. He had "cradle cap" as an infant that became generalized to his face followed by his upper torso. Throughout his life he has had intermittent flares of erythematous, scaling patches on his cheeks, chest, and abdomen. His mother expresses frustration with the doctors' inability to help her son's skin. She has used moisturizers and 1% hydrocortisone cream episodically in the past. Recently he seems frequently scratch behinds his knees. She admits that they are more successful in controlling his asthma that was diagnosed about one year ago.

Exam VS are normal. He is alert and not toxic. His exam findings are only positive for erythematous, scaling patches on his cheeks, chest, and abdomen.

Atopic dermatitis (AD) tends to start in infancy and early childhood, usually before the age of 5 years. Common elements of AD include pruritus, eczematous lesions, xerosis (dry skin), and lichenification (thickened skin with accentuated skin markings, sometimes called "elephant skin"). Additional common features are periauricular fissures, cheilitis (lip inflammation and cracking, particularly at the mouth corners), and susceptibility to Staphylococcus aureus skin infections. The term “atopy” is used to describe the triad of atopic eczema, asthma, and allergic rhinitis.

Epidemiologically, the prevalence rate of atopic dermatitis is increasing worldwide. It is estimated that AD affects 10% to 20% of the population. There does seem to be some variation in rates from one ethnic or geographic area to another. Reported rates can run from greater than 20% in Scandinavian populations to less than 5% in east Africa.

Atopic dermatitis is thought to occur through an interaction between genetic and environmental factors. Studies of twins have shown a higher concordance for the disease in identical twins compared to dizygotic twins. While parental, especially maternal, history of atopy has been found to be one of the strongest risk factors in the development of atopy, environmental factors such as climate and degree of urbanization may be credited for the increasing prevalence and possible severity of atopic dermatitis. There is a strong relationship between atopic dermatitis and other IgE-associated diseases such as food allergies, asthma, allergic rhinitis, and urticaria.

Diagnostic criteria for atopic dermatitis include pruritus and three or more of the following features:
- History of involvement of the skin creases (elbow folds, behind the knees, front of ankles, around the neck).
- Past medical history of asthma or hay fever.
- History of generally dry skin over the last year.
- Visible flexural eczema (or eczema involving cheeks, forehead, extensor limbs in children under age of 4 years).
- Onset of less than age 2 years (not used unless child is under 4 years of age).

There are two proposed hypotheses for the pathophysiology in the development of atopic dermatitis. The first describes a primary immune dysfunction that results in IgE sensitization and a secondary epithelial-barrier disturbance. The second suggests a primary problem in the epithelial barrier leading to secondary immunologic dysregulation that results in inflammation. Atopic dermatitis characteristically displays two immune responses: 1) IgE overproduction and 2) diminished cell mediated immunity. T-cells produce cytokines, such as IL-4 and IL-5, which yield elevated IgE levels. It is hypothesized that an overwhelming T-cell activity that produces this aberrant lymphokine profile limits cellular immune response. This in turn may increase susceptibility to certain microorganisms. House dust mite, animal dander, and certain pollens are related to atopic dermatitis exacerbations.

Concerned parents often raise the question of the relationship between food allergies and atopic dermatitis. Food allergies occur in up to 40% of infants and children with moderate to severe atopic dermatitis. Evidence suggests that atopic dermatitis is a precursor to allergic disease and potential future food allergies rather than a consequence of it. A food allergy tends to occur within 30 minutes of exposure to the allergen with such cutaneous symptoms as hives and itching of the lips. More severe potential reactions include respiratory or gastrointestinal problems, or anaphylaxis. It should be noted that sensitization to food is not the same as being allergic to food. Sensitization to food is determined by the presence of specific IgE antibodies in the blood that can be demonstrated by blood or skin tests. Atopic dermatitis patients have generally elevated IgE levels that may result in positive tests; however to diagnose a food allergy requires a strong history of reaction or verification via food challenge. Current guidelines recommend that children less than 5 years of age with moderate to severe atopic dermatitis be considered for food allergy evaluation for milk, egg, peanut, wheat, and soy if the atopic dermatitis persists despite optimized management or if there is a reliable history of immediate reaction after ingestion of a specific food.

The differential diagnoses for an eczematous dermatitis is broad and includes seborrheic dermatitis, scabies, allergic contact dermatitis, and several immune disorders. Distinguishing between atopic and seborrheic dermatitis often depends on the age and distribution of the rash. In early infancy, seborrheic dermatitis usually presents earlier than 2 months of age with AD presenting thereafter. Seborrhea has a much better prognosis, and usually resolves by six months of age, just when atopic dermatitis becomes more prevalent. Seborrheic dermatitis favors areas of high sebum production and the larger body folds. Pruritus is absent in seborrhea but is always present in AD. Infantile seborrheic dermatitis tends to present as greasy scale over the scalp (cradle cap), but there can also be patches of erythema on the scalp, face, retroauricular folds, neck, trunk and proximal extremities. The rash itself is difficult to distinguish morphologically from atopic dermatitis. In older children, scabies can cause discrete areas of pruritus with papules and scaly erythema, but usually these show a predilection for the hands, feet, and genital areas. One will often find the tiny burrow wounds on close inspection, often in the web spaces between the fingers. Allergic contact dermatitis is more sudden in onset and less relapsing in course. Usually a specific new allergen can be identified by history, and a very specific distribution of dermatitis is often helpful in its diagnosis.

Several more severe immune-related disorders should be considered depending on the patient’s age and clinical presentation. Hyper-IgE syndrome (Job's syndrome) may be inherited in an autosomal dominant or autosomal recessive fashion, and features very high levels of IgE and more severe infections of tissues other than the skin, such as pneumonias, sinusitis, or deep soft tissue abscesses. Characteristic facial features as well as eosinophilia, and delayed loss of primary teeth are also seen. Wiskott-Aldrich syndrome is an X-linked recessive disorder that can appear clinically as AD, but it is also associated with thrombocytopenia and recurrent bacterial infections. X-linked Bruton's agammaglobulinemia can also produce similar rashes but shows low IgE levels. Langerhans cell histiocytosis (histiocytosis-X) can involve many organ systems but can superficially resemble seborrheic dermatitis.

As is the case with acne, the level of therapy should be tailored to the severity of the disease. AD patients tend to have dry skin, which results in decreased epidermal barrier protection and increased risk of antigen stimulation of the underlying tissues. Moisturizers can help to restore the epidermal barrier and play a key role in the management of AD. Emollients are best, particularly after bathing, although a very greasy product may not be well tolerated by older patients. Systemic antihistamines may help with pruritus. Sedating antihistamines, such as hydroxyzine or diphenhydramine, are particularly helpful in managing bedtime/nocturnal scratching.

Topical corticosteroids are frequently the first line of medicated therapy. The lowest potencies are 0.5%, and 1% hydrocortisone, which are over-the-counter. For more resistant cases, one will probably have to use higher potency prescription steroid preparations. In pediatric patients, mometasone 0.1% cream or triamcinolone 0.1% cream are used for flare-ups or more persistent, thicker areas of AD. There is a concern of systemic absorption of topical corticosteroids, but many studies have failed to show an actual adverse effect unless there was long-term use. Potent topical corticosteroids can cause skin thinning and striae if used repeatedly or over long periods of time. Newer FDA-approved topical medications for atopic dermatitis are the non-steroidal immunomodulators tacrolimus (Protopic) ointment and pimecrolimus (Elidel) cream. Unlike corticosteroids, these calcineurin inhibitors can be safely used for long periods of time without the side effects seen in corticosteroids. Severe, body-wide exacerbations of AD may require short bursts of systemic corticosteroids (such as 1 mg/kg per day of oral prednisolone), which is often successful in improving the severe flare within a few days. Other treatments that have been used in recalcitrant cases of AD in pediatric patients include ultraviolet B (UVB), ultraviolet A (UVA), PUVA (psoralen plus UVA), cyclosporine, azathioprine, and mycophenolate mofetil.

Seborrheic dermatitis is usually managed somewhat differently than AD. Because infantile seborrheic dermatitis is usually mild and self-limited, it often responds to simple skin care measures. Parents can use a mild baby shampoo to gently remove scalp scale and crusts. Ketoconazole 2% cream can be used in more extensive or persistent cases. When the condition is more inflamed, mild corticosteroid creams can provide great benefit.

Questions

1. True/False: Seborrhea starts in infancy at the same time as atopic dermatitis.

2. True/False: The prevalence of atopic dermatitis is generally higher in more industrialized societies and may be in part related to diverse environmental stimuli present in these communities.

3. True/False: Moisturizers that restore the epidermal barrier are the mainstay of atopic dermatitis treatment and prevention.

4. Which of the following is a true statement?
. . . . . a. Seborrhea produces dry scales on the scalp of infants.
. . . . . b. Both seborrhea and atopic dermatitis benefit from scale removal.
. . . . . c. Seborrhea is not pruritic.
. . . . . d. Hydrocortisone cream should be used in cradle cap dermatitis.

5. Which of the following corticosteroid preparations are available over the counter?
. . . . . a. triamcinolone cream
. . . . . b. oral prednisolone
. . . . . c. mometasone cream
. . . . . d. hydrocortisone cream

References

1. Atopic Dermatitis. In: Bolognia JL, Jorizzo JL, Rapini RP (Ed). Dermatology, 2nd Edition. Amsterdam: Mosby Elsevier, 2008. pp. 181-195.

2. Other Eczematous Eruptions. In: Bolognia JL, Jorizzo JL, Rapini RP (Ed). Dermatology, 2nd Edition. Amsterdam: Mosby Elsevier, 2008. pp. 181-195.

3. American Academy of Dermatology. “Dermatologists caution that atopic dermatitis is a strong precursor to food allergies.” Science Daily, 4 February 2011. Web. 30 May 2013. www.sciencedaily.com/releases/2011/02/01/110205140828

4. Atopic dermatitis, eczema, and non-infectious immunodeficiency disorders. In: James WD, Berger T, Elston D (Ed). Andrews’ Diseases of the Skin, 10th Edition. Philadelphia: W.B. Saunders Company. 2006. pp. 69-76

5. Stokowski, LA. “Food Allergy in Dermatology: The Patient With Atopic Dermatitis, Highlights of the NIAID Guidelines.” Medscape Allergy & Immunology. 17 May 2011. Web. 30 May 2013. http://www.medscape.com/viewarticle/738815

Answers to questions

1. False. Seborrhea presents earlier (less than 2 months).

2. True

3. True

4. c. Seborrhea is not pruritic.

5. d. hydrocortisone