Phenytoin ameliorates the memory deficit induced in the young chick by ethanol toxicity in association with thiamine deficiency

Neuroimaging of Wernicke's encephalopathy and Korsakoff's syndrome

There is considerable evidence that neuroimaging findings can improve the early diagnosis of Wernicke's encephalopathy (WE) in clinical settings. The most distinctive neuroimaging finding of acute WE are cytotoxic edema and vasogenic edema, which are represented by bilateral symmetric hyperintensity alterations on T2-weighted MR images in the periphery of the third ventricle, periaqueductal area, mammillary bodies and midbrain tectal plate. An initial bout of WE can result in Korsakoff's syndrome (KS), but repeated bouts in conjunction with its typical comorbidity, chronic alcoholism, can result in signs of tissue degeneration in vulnerable brain regions. Chronic abnormalities identified with neuroimaging enable examination of brain damage in living patients with KS and have expanded the understanding of the neuropsychological deficits resulting from thiamine deficiency, alcohol neurotoxicity, and their comorbidity. Brain structure and functional studies indicate that the interactions involving the thalamus, mammillary bodies, hippocampus, frontal lobes, and cerebellum are crucial for memory formation and executive functions, and the interruption of these circuits by WE and chronic alcoholism can contribute substantially to the neuropsychological deficits in KS.

Neuroanatomy and neuropathology associated with Korsakoff's syndrome

Although the neuropathology of Korsakoff's syndrome (KS) was first described well over a century ago and the characteristic brain pathology does not pose a diagnostic challenge to pathologists, there is still controversy over the neuroanatomical substrate of the distinctive memory impairment in these patients. Cohort studies of KS suggest a central role for the mammillary bodies and mediodorsal thalamus, and quantitative studies suggest additional damage to the anterior thalamus is required. Rare cases of KS caused by pathologies other than those of nutritional origin provide support for the role of the anterior thalamus and mammillary bodies. Taken together the evidence to date shows that damage to the thalamus and hypothalamus is required, in particular the anterior thalamic nucleus and the medial mammillary nucleus of the hypothalamus. As these nuclei form part of wider memory circuits, damage to the inter-connecting white matter tracts can also result in a similar deficit as direct damage to the nuclei. Although these nuclei and their connections appear to be the primary site of damage, input from other brain regions within the circuits, such as the frontal cortex and hippocampus, or more distant regions, including the cerebellum and amygdala, may have a modulatory role on memory function. Further studies to confirm the precise site(s) and extend of brain damage necessary for the memory impairment of KS are required.

The evolution and treatment of Korsakoff's syndrome: out of sight, out of mind?

Wernicke's Encephalopathy is an acute neuro-psychiatric condition caused by an insufficient supply of thiamine (Vitamin B1) to the brain. If undiagnosed or inadequately treated, it is likely to proceed to Korsakoff's Syndrome. Wernicke's Encephalopathy can result from dietary deficiency alone and this form is usually successfully treated, with little chance of Korsakoff's Syndrome supervening. On the other hand, thiamine deficiency associated with alcohol misuse/dependence may require up to 1 gram of thiamine IV in the first 24 hours to be treated successfully. The reasons for this difference in treatment will be discussed. Thiamine diphosphate acts as a co-factor for a number of thiamine-dependent enzymes. Thiamine deficiency leads to a reduction in the activity of these enzymes, and this leads to alterations in mitochondrial activity, impairment of oxidative metabolism, decreased energy status and eventually selective neuronal death. The damage caused by the combination of thiamine deficiency and alcohol metabolism probably interferes with adequate thiamine transport at a number of sites in the body, including the blood-brain barrier, as well as causing damage to the apoenzymes which then require higher concentrations of thiamine to work normally. The accumulated damage is likely to render the use of oral thiamine therapeutically inadequate since the body is unable to produce high enough concentrations of thiamine in the blood to traverse the blood-brain barrier. Some individuals are probably genetically predisposed to develop Wernicke's. Long before individuals with alcohol misuse or dependence develop Wernicke's Encephalopathy the neurons and other cells of the body are functioning sub-optimally because of the inadequate supply of thiamine and the neurotoxic effect of alcohol. This relative deficiency initiates a series of pathological changes which accumulate and further interfere with the supply of thiamine and its utilisation at a time when the requirements are increased. The best treatment for Korsakoff's Syndrome is timely recognition of Wernicke's Encephalopathy and appropriate intervention and prevention.

Alcohol dementia and thermal dysregulation: a case report and review of the literature

Wernicke's encephalopathy and Korsakoff's psychosis in alcoholics are thought to be due to thiamine deficiency. When the process goes untreated, patients may develop alcohol-induced persisting dementia. We review the literature on thermal dysregulation and the place of thiamine treatment in Wernicke's encephalopathy, Korsakoff's psychosis, and alcohol-induced persisting dementia. We describe a patient with alcohol-induced persisting dementia who showed thermal dysregulation which responded to parenteral but not oral thiamine. Subsequently, he developed aspiration pneumonia with associated fever reaction and expired. We describe the neuroimaging findings--diffuse cortical atrophy, ventricular dilatation, atrophy of the corpus callosum, hypothalamus, and medulla, and a probable arachnoid cyst in the left temporal tip. We conclude that thermal dysregulation was likely related to dysfunction of temperature regulatory brain centers, that thermal dysregulation was stabilized with parenteral but not oral thiamine, and that parenteral thiamine may have a role even in chronic cases of alcohol-induced persisting dementia.

Interaction of thiamine deficiency and voluntary alcohol consumption disrupts rat corpus callosum ultrastructure

The relative roles of alcohol and thiamine deficiency in causing brain damage remain controversial in alcoholics without the Wernicke-Korsakoff syndrome. Experimental control over alcohol consumption and diet are impossible in humans but can be accomplished in animal models. This experiment was designed to differentiate the separate and combined effects on the macro- and ultrastructure of the corpus callosum of thiamine deficiency and voluntary alcohol consumption. Adult male alcohol-preferring (P) rats (9 chronically alcohol-exposed and 9 water controls) received a thiamine-deficient diet for 2 weeks. There were four groups: five rats previously exposed to alcohol were treated with pyrithiamine (a thiamine phosphorylation inhibitor); five rats never exposed to alcohol were treated with pyrithiamine; four alcohol-exposed rats were treated with thiamine; and four rats never exposed to alcohol were treated with thiamine. On day 14, thiamine was restored in all 18 rats; 2 weeks later the 10 pyrithiamine-treated rats received intraperitoneal thiamine. The rats were perfused 61 days post-pyrithiamine treatment at age 598 days. Brains were dissected and weight and volumes were calculated. Sagittal sections were stained to measure white matter structures. The corpus callosum was examined using transmission electron microscopy to determine density of myelinated fibers, fiber diameter, and myelin thickness. The corpus callosum in the alcohol/pyrithiamine group was significantly thinner, had greater fiber density, higher percentage of small fibers, and myelin thinning than in the alcohol/thiamine and water/thiamine groups. Several measures showed a graded effect, where the alcohol/pyrithiamine group had greater pathology than the water/pyrithiamine group, which had greater pathology than the two thiamine-replete groups. Across all 16 rats, thinner myelin sheaths correlated with higher percentage of small fibers. Myelin thickness and axon diameter together accounted for 71% of the variance associated with percentage of small fibers. Significant abnormalities in the alcohol/pyrithiamine group and lack of abnormality in the alcohol-exposed/thiamine-replete group indicate that thiamine deficiency caused white matter damage. The graded abnormalities across the dually to singly treated animals support a compounding effect of alcohol exposure and thiamine depletion, and indicate the potential for interaction between alcohol and thiamine deficiency in human alcohol-related brain damage.

The natural history and pathophysiology of Wernicke's Encephalopathy and Korsakoff's Psychosis

AIMS

To identify the early clinical indications of thiamine deficiency and to understand the factors involved in the development of the amnesic state in alcohol-dependent individuals with thiamine deficiency. It is hoped that this will highlight the need for clinicians to treat alcohol-dependent patients prophylactically with parenteral thiamine and thus prevent the development of Korsakoff's Psychosis (KP).

METHOD

We have reviewed the natural history and pathophysiology of Wernicke's Encephalopathy (WE) in both human and animal studies together with any contributory factors that may predispose the individual to thiamine deficiency. A further understanding of these problems is provided by recent studies into the metabolic consequences of thiamine deficiency and alcohol misuse.

CONCLUSIONS

Where WE is due to thiamine deficiency alone (i.e. in the absence of alcohol misuse) KP rarely supervenes following thiamine replacement therapy. Successful treatment or prophylaxis of WE in alcohol dependence probably depends on a number of inter-related issues and is not simply a matter of early and adequate thiamine treatment. If sufficient alcohol-related neurotoxicity has occurred by the time of diagnosis, then this may be the more important or limiting factor with respect to the long-term outcome. This possible obstacle to complete recovery should not prevent every attempt being made to provide the patient with optimum brain thiamine replacement.

Facilitation of a weak training experience in the 1-day-old chick using diphenylhydantoin: a pharmacological and biochemical study

This series of studies used a weakly trained (20% methyl anthranilate) version of the passive avoidance learning task in the 1-day-old chick to investigate memory facilitation effects by diphenylhydantoin (DPH). The results indicated that the pairing of the weak training experience with DPH results in facilitation of memory that can be observed from 40 min following training with the weak training experience. The results from a biochemical experiment indicated that DPH facilitates the activity of Na(+)/K(+)-ATPase at the majority of times sampled in a large percentage of the sections of the chick brain. The most marked level of elevation in the activity of the enzyme was observed at the 20-min time point following weak training in the section of the chick brain, which contained several memory relevant neuroanatomical loci. This represents a 68% increase in the activity of the enzyme in those areas considered to be crucial to the processing of memory in the paradigm at a time predicted by previous investigation to be crucial in the development of the intermediate-term memory stage of memory. The results of this series of studies support the notion that Na(+)/K(+)-ATPase plays an important role in memory processing following passive avoidance training in the 1-day-old chick.