Heavy drinking in people who also have thiamine deficiency, usually caused by poor nutrition, can lead to two neuropsychiatric disorders, one of which is reversible (Wernicke’s encephalopathy) and the other is not (Korsakoff’s psychosis). These syndromes are now considered a unitary disorder called Wernicke–Korsakoff syndrome. Wernicke’s encephalopathy is characterized by a confusional state, ataxia, abnormal eye movements, blurred vision, double vision, nystagmus, and tremor. It is associated with a prolonged history of alcoholism with steady drinking and an inadequate nutritional state. The neurological syndrome (ataxia, opthalmoplegia, and nystagmus) can be reversed in its early stages by thiamine supplementation in the diet, but the learning and memory impairments respond more slowly and incompletely. Untreated Wernicke’s encephalopathy leads to death in up to 20% of cases, and a large percentage (85%) of people who survive Wernicke’s encephalopathy go on to develop Korsakoff’s psychosis.
Korsakoff’s psychosis is characterized by severe anterograde amnesia with intact retrograde memory (that is, memories prior to the onset of Korsakoff’s remain intact). Other cognitive functions may be spared, but the amnesia is irreversible and is associated with actual loss of neurons in the brain, such as anterior portions of the diencephalon, including the paratenial nucleus, mesial temporal lobe structures, orbitofrontal cortices, nucleus basalis, basal forebrain structures, and the hippocampus.