Allergy in early and late onset of atopic dermatitis

The main criteria of atopic dermatitis (AD) are based on symptoms and signs such as pruritus and age-related typical distribution and morphology of the eczema (1). AD is frequently associated with other atopic manifestations, e.g. asthma and allergic rhinoconjunctivitis (ARC), clinical allergies to, for example, pollen and danders and positive tests for allergy, e.g. RAST. AD often starts in infancy and early appearing AD and a family history of atopic disease are possible means of selecting infants at high risk for future allergy (2 , 3). In this study we have analysed if an onset of AD before two years of age implies a heavier allergy trait than AD with a later onset, by re-evaluating data from our previous prospective studies on sensitization in infants and children (2-4). One cohort of 84 girls was unselected with regard to family history of atopy (NR, normal risk), and they were followed from birth with interviews, examinations and tests at ages 3 and 8 months, and 2 ,4 ,7 and 12 years (2, 4). The initial cohort consisted of 86 children. Two nonatopic children died between 7 and 12 years. The remaining 84 children reported for all follow-up evaluations. Another cohort consisted of 115 children selected from families with atopic diseases in at least two close relatives or with single heredity and cord blood IgE 80.9 kUjl (HR, high risk) (3). The initial cohort comprised 121 children but the parents of 6 children objected to the venepunctures before or at the first follow-up examination. The remaining 1 15 children were followed from birth with interviews, examinations and tests at ages 3,6 and I8 months, and 2 and 4 years. The mothers of 65 of the 11 5 HR children were on restricted diets during lactation. The criteria of atopic manifestations and clinical allergy have been described in detail previously (2, 3). Briefly, AD was defined exclusively on the basis of its dermatological manifestations, i.e. chronic or chronically relapsing, non-infectious dermatitis of typical morphology and distribution, based on the suggestions of Hanifin 8.1 Rajka (1). Three or more episodes of bronchial obstruction were regarded as athma. Rhinitis was considered allergic if it appeared at least twice after exposure to a particular allergen. Positive exposure to an allergen was defined as an obvious reaction within 1 h on at least two occasions. The two cohorts of children were divided in three subgroups each: (group I) children with onset of AD before two years of age (12 NR children, 37 HR children); (group 11) children with onset of AD after two years of age (14 NR children, 10 HR children); and (group 111) children who did not develop AD during the period of follow-up (58 NR children, 68 HR children). IgE antibodies were determined by Phadebas Rast (Pharmacia Diagnostics AB, Uppsala, Sweden). Only IgE antibody concentrations 2 0.35 PRUjml, i.e. RAST class level 1 or higher, were regarded as positive. RAST was performed against the following allergens: egg white, cow’s milk, mite ( D . pteronyssimus), birch, timothy and mixed animal danders (cat, cow, horse, dog). The subgroups of NR and HR children were evaluated with regard to the cumulative frequencies of asthmajARC, clinical allergy to pollen or danders, positive RAST to egg white or cow’s milk, and positive RAST to inhalants. Since the samples were small and the expected frequencies were sometimes less than 5, Fisher’s exact test (two-tailed) was used to analyse possible differences between the subgroups of children. The results are shown in Table 1. For NR children the cumulative frequencies of all the markers of allergy were significantly higher in children with AD before two years of age than in children with onset of AD after two years and in children without AD. Children with onset of AD after two years did not differ from children without AD. In the HR group children with onset of AD before two years of age differed significantly from children with onset after two years only for a higher frequency of positive RAST to food antigens. Children with onset of AD before two years of age had higher frequencies of all markers of allergy than children without AD, while children with onset of AD after two years had a significantly higher frequency than children without AD only with regard to a positive RAST to inhalants.