MRI of the 'Alzheimer syndrome'

Abstract

Interest in the identification of cognitive decline in its earliest manifestations and the heterogeneity of clinically diagnosed Alzheimer's disease (AD) explain the growing number of neuroimaging studies of AD. Alzheimer-type lesions are associated with loss of neurons, and magnetic resonance imaging (MRI) can detect predominantly left atrophic changes in the entorhinal cortex, amygdala and anterior hippocampus several years before the onset of clinical symptoms. Cerebrovascular disease can mimic AD in the elderly whereas MR markers of subcortical vascular disease-leukoaraiosis, lacunar infarcts, microbleeds, ventricular enlargement, cortical and hippocampal atrophy-appear to be structural changes associated with vascular-related cognitive impairment. Furthermore, analysis of prodromal forms of late-onset dementia of Alzheimer's type (DAT) differentiates amnesic single-domain mild cognitive impairment, which shows MR patterns similar to those observed in early-onset DAT, from other predementia patterns without atrophy at the earliest sites of AD pathology. Mesiotemporal atrophy on MRI predicts late-onset DAT, but the current rating scales or measurements of mesiotemporal atrophy do not differentiate anteromesial temporal atrophy that is highly suggestive of AD from predominantly hippocampal atrophy, suggestive of non-AD damage and, usually, vascular disease. The other, most common MRI predictors of late-onset DAT may be considered indirect markers of arterial senescence whereas brain atrophy is diffusely milder and MR markers of small-vessel disease more frequent in late-onset, compared with early-onset, DAT. Thus, MRI suggests an overestimation of AD pathology while underestimating 'arteriosclerotic brain degeneration' in the clinical picture of 'Alzheimer syndrome'.