Mercury poisoning: a rare but treatable cause of failure to thrive and developmental regression in an infant.

An infant presented with failure to thrive and developmental regression. Physical examination revealed an irritable child with swollen, erythematous extremities, and elevated blood pressure. Extensive investigations, including a metabolic work-up and neuroimaging, were unrevealing. Exposure to self-purchased medication was initially denied. The physical signs were suggestive of acrodynia. Mercury poisoning was ultimately established by measuring paired blood and urine mercury levels. On further enquiry, it was revealed that the child had been given a Chinese medicinal product for 4 months. He responded well to a chelating agent. Acrodynia is a childhood disease considered to be of historical interest only, but making a diagnosis of mercury poisoning is rewarding because the response to treatment is good. This case highlights the common misconception that alternative medicines are safe and benign.