Systemically induced allergic exanthem from mercury

Cutaneous reactions to mercury can manifest themselves in different forms. Apart from contact dermatitis, flare-up reactions, disseminated exanthem as well as skin symptoms in previously unaffected skin are known. Regarding systemic allergen application, 2 separate clinical patterns, namely acute generalized exanthematous pustulosis (AGEP) and symmetric flexural exanthem 'baboon syndrome' have been described. Systemic allergic reactions to mercury are most commonly provoked by the inhalation of metallic mercury vapours from a broken thermometer, often after previous sensitization to mercury compounds, e.g. Mercurochrome. Patch testing with mercurials yields positive reactions in approximately 80% of patients. We report 3 patients, 2 with flexural exanthem, and 1 presenting with AGEP, respectively. Positive patch tests to mercury derivatives could be demonstrated in all of them. Furthermore, non-toxic serum mercury levels were detected in 2 of the patients. The present review provides a survey of the literature on systemic allergic exanthem to mercury. However, plausible explanations for the distribution pattern of the skin manifestations in AGEP and flexural exanthem are still lacking.