Clive Harper

The Neuropathology of Alcohol-specific Brain Damage, or Does Alcohol Damage the Brain?

The aim of this review is to identify neuropathological changes that are directly related to the long-term use of excessive amounts of alcohol (ethanol). There is still debate as to whether alcohol per se causes brain damage. The main problem has been to identify those lesions caused by alcohol itself and those caused by other common alcohol-related factors, principally thiamin deficiency. Careful selection and classification of alcoholic cases into those with and without these complications, together with detailed quantitative neuropathological analyses, has provided us with useful data. There is brain shrinkage in uncomplicated alcoholics which can largely be accounted for by loss of white matter. Some of this damage appears to be reversible. However, alcohol-related neuronal loss has been documented in specific regions of the cerebral cortex (superior frontal association cortex), hypothalamus (supraoptic and paraventricular nuclei), and cerebellum. The data is conflicting for several regions: the hippocampus, amygdala and locus ceruleus. No change is found in the basal ganglia, nucleus basalis, or serotonergic raphe nuclei. Many of the regions that are normal in uncomplicated alcoholics are damaged in those with the Wernicke-Korsakoff syndrome. Dendritic and synaptic changes have been documented in uncomplicated alcoholics and these, together with receptor and transmitter changes, may explain functional changes and cognitive deficits that precede the more severe structural neuronal changes. The pattern of damage appears to be somewhat different and species-specific in animal models of alcohol toxicity. Pathological changes that have been found to correlate with alcohol intake include white matter loss and neuronal loss in the hypothalamus and cerebellum.

Operational criteria for the classification of chronic alcoholics: identification of Wernicke's encephalopathy.

OBJECTIVES: To establish better operational criteria for the diagnosis of Wernickes encephalopathy. Current criteria for diagnosing Wernickes encephalopathy require the presence of three clinical signs (oculomotor abnormalities, cerebellar dysfunction, and an altered mental state), although it has often been reported that most patients do not fulfil all these criteria. METHODS: The clinical histories of 28 alcoholics with neurological and neuropsychological assessments and definitive neuropathological diagnoses were examined to determine clinical signs for use in a screening schedule. Operational criteria were then proposed for differentiating patients with Wernickes encephalopathy alone or in combination with Korsakoffs psychosis or hepatic encephalopathy. The new criteria for Wernickes encephalopathy require two of the following four signs; (1) dietary deficiencies, (2) oculomotor abnormalities, (3) cerebellar dysfunction, and (4) either an altered mental state or mild memory impairment. Reproducibility and validity testing of these criteria were performed on 106 alcoholics screened from a large necropsy sample. RESULTS: Despite rater variability with regard to specific symptoms, within and between rater reliability for diagnostic classification using the criteria retrospectively on patient records was 100% for three independent raters. Validity testing showed that Wernickes encephalopathy was underrecognized only when occurring with hepatic encephalopathy (50% sensitivity). CONCLUSIONS: By contrast with current criteria, the proposed operational criteria show that the antemortem identification of Wernickes encephalopathy can be achieved with a high degree of specificity.

The Neuropathology of Alcohol-Related Brain Damage

Excessive alcohol use can cause structural and functional abnormalities of the brain and this has significant health, social and economic implications for most countries in the world. Even heavy social drinkers who have no specific neurological or hepatic problems show signs of regional brain damage and cognitive dysfunction. Changes are more severe and other brain regions are damaged in patients who have additional vitamin B1 (thiamine) deficiency (Wernicke-Korsakoff syndrome). Quantitative studies and improvements in neuroimaging have contributed significantly to the documentation of these changes but mechanisms underlying the damage are not understood. A human brain bank targeting alcohol cases has been established in Sydney, Australia, and tissues can be used for structural and molecular studies and to test hypotheses developed from animal models and in vivo studies. The recognition of potentially reversible changes and preventative medical approaches are important public health issues.

Are we drinking our neurones away

A quantitative neuropathological necropsy study of the human cerebral cortex showed that the number of cortical neurones in the superior frontal cortex in chronic alcoholic patients is significantly reduced compared with that in controls matched for age and sex. The number of neurones in the motor cortex did not differ significantly between the controls and alcoholics, but in both cortical regions there was evidence that alcoholic patients had smaller (shrunken) neurones than controls. Further studies are necessary to identify other regions of the cerebral cortex that are selectively damaged in brain damage associated with alcohol.

Brain shrinkage in chronic alcoholics: a pathological study.

A quantitative neuropathological necropsy study of 22 control and 22 chronic alcoholic subjects showed a statistically significant loss of brain tissue in the chronic alcoholic group. The loss of tissue appeared to be from the white matter of the cerebral hemispheres rather than the cerebral cortex. This may reflect a primary alteration in the composition or structure of the white matter or it may be secondary to loss of nerve cells from the cortex with subsequent degeneration of the axons in the white matter. Further morphometric analyses including cortical neuronal counts will be necessary to clarify this issue.

Neuropathological alterations in alcoholic brains. Studies arising from the New South Wales Tissue Resource Centre

Alcohol dependence and abuse are among the most costly health problems in the world from both social and economic points of view. Patterns of drinking appear to be changing throughout the world with more women and young people drinking heavily. Excessive drinking can lead to impairment of cognitive function and structural brain changes--some permanent, some reversible. Patterns of damage appear to relate to lifetime alcohol consumption but, more importantly, to associated medical complications. The most significant of these is the alcohol-related vitamin deficient state, the Wernicke-Korsakoff syndrome (WKS), which is caused by thiamin deficiency but is seen most commonly in alcoholics. Careful selection and classification of alcoholic cases into those with and without these complications, together with detailed quantitative neuropathological analyses has provided data that gives clues to the most vulnerable regions and cells in the brain. Brain shrinkage is largely accounted for by loss of white matter. Some of this damage appears to be reversible. Alcohol-related neuronal loss has been documented in specific regions of the cerebral cortex (superior frontal association cortex), hypothalamus and cerebellum. No change is found in basal ganglia, nucleus basalis, or serotonergic raphe nuclei. Many of these regions which are normal in uncomplicated alcoholics are damaged in those with the WKS. Dendritic and synaptic changes have been documented in alcoholics and these, together with receptor and transmitter changes, may explain functional changes and cognitive deficits, which precede more severe structural neuronal changes. A resource to provide human brain tissues for these types of studies has been developed at the University of Sydney--the New South Wales Tissue Resource Centre. The aim of this facility is to provide research groups throughout the world with fresh and/or frozen tissues from well-characterized cases of alcohol-related brain damage and matched controls. The development of new technologies in pathology and molecular biology means that many more questions can be addressed using appropriately stored human brain tissues. Examples of the application of some of these techniques, involving neurochemical, neuropharmacological, neuroimaging and gene expression studies are included in this paper. Important public health outcomes have arisen from some of these studies including the enrichment of bread flour with thiamin for the whole of Australia. Researchers with an interest in alcohol studies can access tissues from this brain bank.

Neuronal loss in functional zones of the cerebellum of chronic alcoholics with and without Wernicke's encephalopathy

This study examines the effect of chronic alcohol consumption on the human cerebellum using operational criteria for case selection [Caine D. et al. (1997) J. Neurol. Neurosurg. Psychiat. 62, 51-60] and unbiased stereological techniques. We describe, for the first time, structural changes in different functional zones of the cerebellum of chronic alcoholics and correlate these changes with specific clinical symptoms. No consistent changes in the number of neurons or the structural volume for any cerebellar region were observed in the chronic alcoholics without the clinical signs of Wernickes encephalopathy. In all cerebellar measures, these chronic alcoholics did not differ significantly from the non-alcoholic controls, suggesting that chronic alcohol consumption per se does not necessarily damage human cerebellar tissue. However, several cerebellar changes were noted in the thiamine-deficient alcoholics studied. There was a significant decrease in Purkinje cell density (reduced on average by 43%) and molecular layer volume (reduced by 32%) in the cerebellar vermis in all thiamine-deficient chronic alcoholics. A decrease in cell density and atrophy of the molecular layer, where the dendritic trees of the Purkinje cells are found, without significant cell loss suggests loss of cellular dendritic structure and volume. These thiamine-deficient alcoholics also had a significant decrease (36% loss) in the estimated Purkinje cell number of the flocculi, disrupting vestibulocerebellar pathways. These results indicate that cerebellar Purkinje cells are selectively vulnerable to thiamine deficiency. There is evidence that this damage contributes significantly to the clinical signs of Wernickes encephalopathy. There was a 36% loss of Purkinje cells in the lateral lobe in alcoholics with mental state signs and 42% atrophy of vermal white matter in ataxic alcoholics. The finding of a 57% loss of Purkinje cells and a 43% atrophy of the molecular layer of the vermis in alcoholics with cerebellar dysfunction supports previous findings highlighting the importance of spinocerebellar pathways to these symptoms.

Clinical and pathological features of alcohol-related brain damage

One of the sequelae of chronic alcohol abuse is malnutrition. Importantly, a deficiency in thiamine (vitamin B1) can result in the acute, potentially reversible neurological disorder Wernicke encephalopathy (WE). When WE is recognized, thiamine treatment can elicit a rapid clinical recovery. If WE is left untreated, however, patients can develop Korsakoff syndrome (KS), a severe neurological disorder characterized by anterograde amnesia. Alcohol-related brain damage (ARBD) describes the effects of chronic alcohol consumption on human brain structure and function in the absence of more discrete and well-characterized neurological concomitants of alcoholism such as WE and KS. Through knowledge of both the well-described changes in brain structure and function that are evident in alcohol-related disorders such as WE and KS and the clinical outcomes associated with these changes, researchers have begun to gain a better understanding of ARBD. This Review examines ARBD from the perspective of WE and KS, exploring the clinical presentations, postmortem brain pathology, in vivo MRI findings and potential molecular mechanisms associated with these conditions. An awareness of the consequences of chronic alcohol consumption on human behavior and brain structure can enable clinicians to improve detection and treatment of ARBD.

Neuronal counts from four cortical regions of alcoholic brains

SummaryNeuronal loss from the frontal superior cortex of the brains of alcoholics has recently been documented. In addition to this, a reduction in the mean neuronal area was also seen in the frontal and motor cortices. This suggested a regional specificity of neuronal damage in the brains of alcoholics. Further quantitation of other cortical regions of the same cases as used in the above study has been performed. The frontal cingulate and temporal cortices were examined and there was found to be no significant alteration in the number of neurons when compared to a control population. There was, however, a significant reduction in the mean size of the neuronal soma in the frontal cingulate cortex (P < 0.05). These data support the hypothesis of regional variations in the severity of cerebral cortical damage in alcoholism with shrinkage of neurons in most regions examined but neuronal loss only in the superior frontal gyrus.

Postmortem MR imaging of formalin-fixed human brain

High-resolution postmortem neuroimaging of the brain can play a role in research programs by providing archival and reslicable images of brain specimens before permanent sectioning. These images can supplement evidence attained from both traditional neuropathological observations and in vivo neuroimaging. Differential brain tissue conspicuity, detectable with MRI, is determined by the density and mobility of water protons. Water content is about 70% in white matter, 80% in gray matter, and 99% in cerebrospinal fluid (CSF). To the extent that brain tissue contrast is determined by the number and microenvironment of water protons, timing parameters of MR image acquisition can interrogate this environment. Because the chemical environment of protons is different in living from dead tissue, optimal temporal imaging parameters, for example, for spin-echo imaging, commonly used for in vivo clinical and research study are different from those best for postmortem imaging. Here, we present a series of observations to identify relaxation times and optimal parameters for high-resolution structural imaging of formalin-fixed postmortem brain tissue using commercially available clinical scanners and protocols. Examples of high-resolution images and results from attempts at diffusion imaging are presented.