Diffusion tensor imaging of white matter degeneration in Alzheimer's disease and mild cognitive impairment.

Alzheimer's disease (AD) has traditionally been regarded as a disease of the gray matter (GM). However, the advent of diffusion tensor imaging (DTI) has contributed to new knowledge about how changes in white matter (WM) microstructure in vivo may be directly related to the pathophysiology of AD. It is now evident that WM is heavily affected in AD, even at early stages. Still, our knowledge about WM degeneration in AD is poor compared to what we know about GM atrophy. For instance, it has not been clear if WM can be directly affected in AD independently of GM degeneration, or whether WM changes mainly represent secondary effects of GM atrophy, e.g. through Wallerian degeneration. In this paper, we review recent studies using DTI to study WM alterations in AD. These studies suggest that microstructural WM affection at pre-AD stages cannot completely be accounted for by concomitant GM atrophy. Further, recent research has demonstrated relationships between increased cerebrospinal fluid levels of Tau proteins and changes in WM microstructure indexed by DTI, which could indicate that WM degeneration in pre-AD stages is related to ongoing axonal damage. We conclude that DTI is a promising biomarker for AD, with the potential also to identify subgroups of patients with especially high degree of WM affection, thereby contributing to more differentiated pre-AD diagnoses. However, more research and validation studies are needed before it is realistic to use this information in clinical practice with individual patients.

Mini-mental state examination is sensitive to brain atrophy in Alzheimer's disease.

BACKGROUND/AIMS: Screening instruments such as the Mini-Mental State Examination (MMSE) are useful for the early identification of Alzheimer's disease (AD). We tested whether macrostructural differences in brain volume are related to the MMSE. METHODS: The MMSE was related to cortical thickness and the volume of 19 brain structures in 96 patients with mild to moderate AD. In addition, the patients were compared to 93 healthy elderly controls. RESULTS: The MMSE was related to the volume of the total brain, cerebral cortex, accumbens, cerebral white matter, inferior lateral ventricles and hippocampus. Positive correlations with cortical thickness were found for 41% of the brain surface, and 58% of this area was significantly thinner in AD. CONCLUSION: The MMSE is sensitive to macrostructural brain atrophy in AD, but also to morphometric variation not specifically related to AD.