Outcome of thiamine treatment in a child with Leigh disease due to thiamine-responsive pyruvate dehydrogenase deficiency

We describe a child with severe psychomotor retardation, peripheral neuropathy and bilateral abnormal signal in basal ganglia on magnetic resonance imaging, consistent with Leigh disease. Fibroblast pyruvate dehydrogenase assayed with routine method was normal. However, because of neurological improvement after treatment with thiamine, pyruvate dehydrogenase activity was studied again with thiamine pyrophosphate concentration adjusted to the normal human tissue level and found to be deficient. We report here on diagnostic difficulties and clinical follow-up of this patient.