A chronic inflammatory skin disorder associated with atopy, causing dry, scaly, itchy lesions.
Atopic tendency in up to 10–25% worldwide. Atopic eczema in 5%.
More common in children with peak onset usually 2–18 months.
M = F
May occur anywhere, but higher incidence in urban areas.
The term atopy is a disease resulting from allergic sensitisation to normal environmental constituents manifesting as asthma, eczema or hayfever. The underlying cause and mechanisms in eczema have yet to be fully elucidated; however, dry skin (xerosis) is an important contributor. There appear to be genetic and immunological components to allergic sensitisation (see also page 498).
· Genetic: Close concordance in monozygotic twins. Offspring of one atopic parent have a 30% risk of being atopic, which rises to 60% if both parents are atopic.
· Chromosome studies suggest that atopic tendency may be inherited in part on maternal 11q13, which codes for the β subunit of mast cell IgE receptors.
· Exacerbating factors include excessive bathing, drying, emotional stress and detergents. Occasionally, in children less than 1-year old milk allergy may be causative.
Serum IgE is elevated in 85% of individuals and higher values are seen when eczema and asthma are present together. It is thought that the high frequency of secondary infection is a combination of the loss of skin integrity and deficiency of local antimicrobial proteins.
Patients have generalised dry skin (xerosis) along with typical eczematous lesions. These are erythematous and scaly, and intense itching results in superficial abrasions (excoriation). Chronic inflammation of the skin causes thickening termed lichenification. Lesions may weep and have tender tiny blisters termed vesicles especially when superinfection occurs. The distribution is age dependent:
· Babies develop eczema predominantly on the face and head; this may resolve or progress by 18 months to the childhood/adult pattern.
· Children and older patients tend to have lesions in the flexures, such as the antecubital and popliteal fossae, neck, wrists and ankles.
Staphylococcus aureus is found on the skin of 90%, which may result in acute infection (impetigenised eczema). Primary infection with herpes simplex may give a very severe reaction known as eczema herpeticum, which in the young may cause dehydration and is life-threatening.
Patients show high levels of serum IgE; suspected allergic triggers may be identified using skin prick or RAST testing.
There is no curative treatment.
Avoidance of exacerbating factors is essential. In babies it may be appropriate to either test for cow’s milk allergy or to perform a therapeutic trial with a cow’s milk protein free formula.
Generalised dry skin (xerosis) requires regular frequent use of emollient moisturisers especially after bathing/showering. Cream preparations are water based with emulsifiers and preservatives and they tend to dry the skin. Greasier preparations such as white soft paraffin achieve better moisturisation. A balance has to be struck between application of sufficient grease and cosmetic satisfaction. Greasier preparations are usually better tolerated prior to going to bed.
Topical steroids remain the mainstay of treatment. If used appropriately they are both safe and effective. The lowest potency that is effective should be used and higher potency reserved for resistant cases. It is also important to use only low-potency steroids on thin areas of skin such as the face.
Antibiotics are used for secondary bacterial infection. In young children these may be parenteral; aciclovir is used to treat eczema herpeticum.
Wet wraps consist of the application of topical agents under bandages to facilitate absorption. Emollients may be administered in this way or coal tar may be used as a keratolytic in lichenified skin. If steroids are applied under wet wraps the dose/potency must be decreased as increased absorption may result in systemic side effects.
Antihistamines have not been shown to be effective in reducing itching. Sedating antihistamines are used at night to improve sleep, reduce nocturnal scratching and hence break the ‘itch-scratch-itch’ cycle.
Topical tacrolimus, an immunosuppressant, is being increasingly used in children prior to the use of high-potency steroids. It appears safe and effective; however, the long-term risks are unknown, as it is a relatively new preparation. Pimecrolimus is under study as a similar agent without systemic immunological effects.
PUVA or combination UVA and UVB are used in very resistant eczema; however, therapy is expensive and increases the risks of skin cancer.
Eczema has a fluctuating course with approximately 50% resolving by 18 months, and few have problems beyond childhood.