Atopic dermatitis ‐ a simple entity?

The application of Occam’s razor, a single unifying cause for a set of observations, is often preached as best clinical practice. In contrast, this memorable young girl illustrates the importance of considering other diagnoses and undertaking appropriate investigations when a common disease is associated with unexplained symptoms. At 15 weeks she presented with vomiting, poor weight gain and a rash, the features of which were consistent with atopic dermatitis (AD). She had a positive family history for atopy and food allergy. Investigations revealed a normal immunoglobulin (Ig) E of 9 kU ⁄ L with a deficiency of all other immunoglobulin classes. Her eczema remained active despite potent topical steroids and antibiotics for recurrent skin infections. By 7 months with immunoglobulin levels starting to rise a diagnosis of transient hypogammaglobulinaemia of infancy (THI) was made. Now age 4 her IgE level is over 5000. She showed multiple positive RAST tests to foods and during a hospital admission for eczema she was started on the few foods diet with a milk-protein-, soyand lactose-free milk substitute. Her skin improved during her stay. At 2 years 7 months her mother reported a rash 90 min after exposure to the sun. Limited phototesting at 300 nm showed erythema down to 2 J ⁄ cm at 24 h with papular responses at higher doses, consistent with a severe polymorphic light eruption. At 2 years 9 months an eczematous eruption across the underwear elastic line raised the suspicion of a contact allergic dermatitis. Patch tests were positive at 96 h to thiuram and mercapto mix giving a diagnosis of a type IV contact allergy to rubber. Rubberand rubberadhesive-free shoes were procured and significantly improved her foot eczema. Despite these avoidance measures the AD remained refractory. A course of beclometasone dipropionate capsules was immediately stopped due to vomiting attributed to intolerance of the lactose component. In 2001 she was registered as having special educational needs due to her need for skin treatments in school and playtime sun avoidance. She has been referred for counselling to the Department of Child Psychiatry. THI is characterized by an abnormal delay in the onset of immunoglobulin synthesis with accentuation and prolongation of the physiological hypogammaglobulinaemia seen in infants. Although rare, THI is more common in individuals with atopic disease or food allergy. This has been postulated as being due to allergen-induced gastrointestinal inflammation accentuating the loss of IgG. In our case THI may have been the reason for a normal IgE despite severe atopic disease. Polymorphic light eruption occurs most commonly in the first three decades and twin studies have suggested a genetic influence. Exacerbation of AD by polymorphic light eruption is known although the prevalence of the coexistence of these two conditions is not. Patch testing is often considered in adults with AD, particularly if the distribution changes. This is also worthwhile in children with AD who give a high yield of positive patch tests, with rubber as a common allergen. The relevance of food avoidance in AD is controversial. 5 This girl continues with dietary manipulation and at times there has been concern over adequate nutrient intake. Her lactose allergy is precluding the use of helpful systemic medication. Severe AD has been shown to have significant psychosocial impact. Counselling is an integral part of all consultations but specialist sessions may be advantageous particularly where behavioural problems impair adherence to treatment. This girl illustrates that optimal management in chronic disease includes appropriate investigation for additional diagnoses when symptoms or signs change. Correspondence: Dr I. C. Pearson, Dermatology Department, St Helier Hospital, Wrythe Lane, Carshalton, SM5 1AA, UK 1 . E-mail: ianpearson@doctors.org. uk