Nickel allergy and hand eczema epidemiological aspects

Abstract: Nickel allergy is the most prevalent contact allergy and has been discussed as a possible riskfactor for hand eczema. However, hand eczema is one of the most frequently occurring skindiseases and has multifactorial origin. The aim of this thesis was to study the association between nickel allergy and hand eczema in the general population. There are only a fewpopulation-based studies previously published, that include patch testing. In addition, this thesis aimed to evaluate methods to follow the prevalence of nickel allergy.The study cohort consisted of 908 women who had been patch tested for the occurrence of nickel allergy as schoolgirls. Twenty years later, they were invited to participate in a follow-up questionnaire study. The response rate was 81%. In total, 17.6% of respondents reported handeczema after the age of 15 years and there was no statistically significant difference in the occurrence of hand eczema between those who were nickel-positive and those who were nickel negativeas schoolgirls. To further investigate possible links, another study was performed,which included a second questionnaire, a clinical investigation and patch testing. All schoolgirls from the baseline study who were still living in the area as adults were invited to participate and the participation rate was 77%. Patch test showed 30.1% nickel-positive individuals.When all participants were included in the analysis, there was no statistically significant difference between nickel-positive and nickel-negative women regarding occurrence of hand eczema. The most important risk factor for hand eczema was childhood eczema. Adjusted prevalence proportion ratio (PPR) for hand eczema after age 15 in relation to nickel patch testresults was 1.03 (95% CI 0.71--1.50) and in relation to childhood eczema 3.68 (95% CI 2.45--5.54). When women with and without history of childhood eczema were analyzed separately, the hand eczema risk was doubled in nickel-positive women without history of childhood eczema. In conclusion, the risk of hand eczema in nickel-positive women may previously havebeen overestimated. Next, the validity of self-reported nickel allergy was investigated. In the established cohort; two questions regarding nickel allergy were compared with patch test results. The validity of self-reported nickel allergy was low, and the questions regarding nickel allergy overestimated the true prevalence of nickel allergy. The positive predictive values were 59% and 60%. Another method for estimating the prevalence of nickel allergy, namely self-patch testing, was validated in the last study. In total, 191 patients from three different dermatology departments participated. The validity of self-testing for nickel allergy was adequate, with sensitivity 72%and proportion of agreement 86%.