Brain Atrophy Rates Vary in Dementias
Brain Atrophy Rates Vary in Dementias
Abstract & Commentary
Source: Chan D, et al. Rates of global and regional cerebral atrophy in AD and frontotemporal dementia. Neurology. 2001;57:1756-1763.
Progressive brain atrophy is one of the characteristic features of Alzheimer’s disease (AD) and the frontotemporal dementias (FTD). MRI volumetry can be used to detect regional differences in the pattern of cortical atrophy in these disorders. However, regional MRI volumetry is technically demanding and time consuming, mitigating against routine clinical use in its present form. Measurement of whole brain atrophy is more easily accomplished, and can be carried out in an automated or semi-automated fashion. British investigators used serial MRI registration techniques to quantify annual rates of cerebral atrophy in 54 patients with AD, 31 with FTD, and 27 controls. They found that the average annual rate of whole brain atrophy in AD and FTD is significantly greater than that of normal brains. However, rate of atrophy did not differentiate patients with AD from those with FTD.
Chan and colleagues obtained serial MRI images on a 1.5 T scanner with an average interscan interval of 12.8 months. They coregistered the images and quantified areas of nonalignment as a measure of atrophic changes. The annual rate of atrophy was significantly greater in demented patients (2.7%) than controls (0.5%). The average rate of atrophy in AD patients (2.4%) was comparable to that of FTD patients (2.7%). While the atrophy rates in AD patients were narrowly distributed (0.5-4.7%), rates in FTD patients varied widely (0.3-8.0%). This variance was interpreted as evidence of greater phenotypic diversity in FTD than AD.
Receiver operating characteristic (ROC) analysis indicated that volumetric measurements distinguished AD from normals with 94% sensitivity and 89% specificity. FTD cases were distinguished from normals at a rate of 83% sensitivity and 89% specificity. The results suggest that measures of whole-brain atrophy can distinguish normals from dementia patients, but do not differentiate between AD and FTD.
Commentary
Brain atrophy measurements represent a potentially promising approach to the dementia diagnosis and follow-up. The technique requires at least 2 MRI scans over a period of a year or more, which limits its value in the initial evaluation of dementia. This study suggests that a straightforward whole-brain atrophy measurement might be useful for distinguishing patients with dementia from normals, an issue that is not always easily resolved when symptoms are mild or when superimposed depression complicates the presentation.
Brain atrophy measurements could also provide a means of assessing therapeutic response to future disease-modifying therapies. In chronic diseases such as AD, brain atrophy measurements provide an index of disease progression which is more to easily related to underlying disease processes than measures such as cognitive status. Atrophy measurements could prove beneficial in evaluating new medications designed to delay or arrest neurodegeneration. As the regional volumetry technology improves, information of relevance to differential diagnosis of dementia may also become available. For now, use of atrophy measurement techniques in the evaluation of dementia is largely confined to the research arena. —Norman Relkin
Dr. Relkin, Associate Professor of Clinical Neurology and Neuroscience, New York Presbyterian Hospital-Cornell Campus, is Assistant Editor of Neurology Alert.
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