RESUMEN
Thiamine is an essential cofactor in the process of nucleic acid synthesis. Neuronal tissues are especially sensitive to thiamine deficiency, manifesting as Wernicke's encephalopathy (WE). The typical triad of WE, encephalopathy, oculomotor dysfunction and gait ataxia, is only present in less than one-third of the cases. We present the case of a middle-aged man with hypoactive delirium due to presumed thiamine deficiency, who had a prolonged hospital course and a delayed diagnosis of the cause of altered mental status. The presentation of this disorder solely as a decreased level of consciousness is uncommon but has been reported in the literature. It is essential to recognise WE as a treatable condition that may manifest only as a hypoactive delirium. The delay in the diagnosis and treatment may lead to coma and death.