Systemic contact dermatitis after oral exposure to nickel: a review with a modified meta-analysis

Systemic contact dermatitis can be elicited experimentally in nickel-sensitive individuals by oral nickel exposure. A crucial point interpreting such experiments has been the relevance of nickel exposure from drinking water and diet. The aim of this meta-analysis study on former nickel-exposure investigations was to provide the best possible estimation of threshold values of nickel doses that may cause systemic contact dermatitis in nickel-sensitive patients. 17 relevant investigations were identified, and statistical analyses were performed in a stepwise procedure. 9 studies were included in the final dose-response analysis, which divided the studies into a homogenous middle group of 5 studies and 2 groups of 2 studies with a higher and lower response frequency, respectively, described by logistic dose-response curves shifted in parallel. On the basis of these curves, calculations were made of the doses that, theoretically, would cause systemic contact dermatitis in exposed nickel-sensitive patients. The results from the 2 most sensitive groups show that 1% of these individuals may react with systemic contact dermatitis at normal daily nickel exposure from drinking water and diet, i.e. 0.22-0.35 mg nickel.