Pink toes and red urine: what is this poison?

A 3.5-year-old boy was found unconscious after ingesting an uncertain amount of a colourless and odourless liquid from a plastic bottle that he found in his mother’s bag. The mother knew that the bottle contained X and immediately took the child to hospital. X was obtained from a jewellery factory in China, and was usually used for electroplating. The child was unconscious, and muscle twitching was noted. His Glasgow Coma Scale (GCS) score was 5/15 (eye, 3; verbal, 1; motor, 1), heart rate was 60 beats/ min, oxygen saturation (SaO2) was 95 to 97% with 100% oxygen supplementation, and blood pressure was undetectable. He developed cardiac arrest and required cardiac massage en route to a regional trauma centre. In the emergency room, intravenous adrenaline, Y and Z, were promptly given. His GCS score was 3/15, pupils 3 mm and reactive, and SaO2 was 90%. Laboratory tests showed that his blood lactate level was 19.7 mmol/L (reference range, 0.5-2 mmol/L), oxyhaemoglobin fraction was 79% (90-95%), carboxyhaemoglobin fraction was 0% (0.5-1.5%), and methaemoglobin fraction was 12.2% (reference level, <2%). The child was intubated, and transferred to the paediatric intensive care unit (PICU). When intravenous W was administered, the urine turned red, indicating the adequacy of treatment (Fig). In the PICU, his pH was 6.98 with base excess of -22 mmol/L. His initial blood cyanide level was 0.75 mg/L. Electroencephalography showed no electrographic seizure. Computed tomography (CT) of the brain showed no cerebral oedema, but magnetic resonance imaging showed oedema bilaterally over the basal ganglia and cerebellum. The child was extubated on the same day, and transferred to the general ward for further care 2 days later. He was noted to have dystonia and fluctuation of mood and behaviour. Subsequently, he developed generalised spasticity and seizure disorder, and CT scan revealed diffuse ischaemic changes.