[Contribution of morphological imaging in the diagnosis of dementia. I--Alzheimer disease]

Diffusion tensor imaging in early Alzheimer's disease

Our aim was to investigate the extent of white matter tissue damage in patients with early Alzheimer disease (AD) using diffusion tensor magnetic resonance imaging (DTI). Although AD pathology mainly affects cortical grey matter, previous magnetic resonance imaging (MRI) studies showed that changes also exist in the white matter (WM). However, the nature of AD-associated WM damage is still unclear. Conventional and DTI examinations (b=1000 s/mm(2), 25 directions) were obtained from 12 patients with early AD (Mini Mental State Examination [MMSE] score=27, Grober and Buschke test score=33.2, digit span score=5.6) and 12 sex- and age-matched volunteers. The right and left mean diffusivity (MD) and fractional anisotropy (FA) of several WM regions were pooled in each patient and control, and compared between the two groups. Volumes of the whole brain and degree of atrophy of the temporal lobe were compared between the two groups. In AD, MD was increased in the splenium of the corpus callosum and in the WM in the frontal and parietal lobes. FA was bilaterally decreased in the WM of the temporal lobe, the frontal lobe and the splenium compared with corresponding regions in controls. Values in other areas (occipital area, superior temporal area, cingulum, internal capsule, and genu of the corpus callosum) were not different between patients and controls. No correlations were found between the MMSE score and the anisotropy indices. Findings of DTI reveal abnormalities in the frontal and temporal WM in early AD patients. These changes are compatible with early temporal-to-frontal disconnections.

Magnetic resonance imaging and computed tomography in Alzheimer's disease

Modern imaging techniques such as X-ray computed tomography (CT) and magnetic resonance imaging (MRI) are widely used in the clinical evaluation of patients with dementia disorders. Computed tomography was introduced for clinical practice in the beginning of the 1970s. The advent of MRI came later with the first equipment used for clinical purposes being introduced in the first half of the 1980s. The two modalities differ in many aspects: CT has a lower contrast resolution compared with MRI and is also faster and often more convenient for patients. In contrast, MRI gives a superior picture of the brain tissue without the use of contrast agents. Moreover, MRI, like CT, does not suffer from bone artifacts. The latter is of special importance in the study of dementia diseases (especially Alzheimer's) where structural changes are present close to the brain. The possibility of image in arbitrary imaging planes also makes MRI more suitable to study structures of relevance in Alzheimer's disease such as the medial temporal lobes and the hippocampal formation.

Risk factors and leukoaraiosis in stroke patients

OBJECTIVES

Although leukoaraosis (LA) is a common CT findings, its pathogenesis remains debated: if small-artery pathology may explain in some cases white matter changes, many other factors, such as hemodynamic perturbations, might also lead to LA. To test these hypothesis, we determined the types of cerebrovascular risk factors associated with leukoaraosis in consecutive patients with acute cerebrovascular event.

PATIENTS AND METHODS

Using CT-scans, we prospectively studied in 610 patients consecutively admitted for an acute cerebral event, the relation between LA and the following cerebrovascular risk factors: age, sex, arterial hypertension, diabetes mellitus, hyperlipemia, alcohol consumption, birth contraceptive pills, previous transient ischemic attack or stroke, migraine, atrial fibrillation, valvulopathy, coronaropathy, left ventricular hypertrophy, stenosis of the internal carotid artery, by means of a multiple linear regression. Relation with cerebral atrophy was also evaluated.

RESULTS

We found LA scores to depend on increasing age (p = 0.0001), female sex (p = 0.0146), history of stroke or TIA (p = 0.0051), history or current atrial fibrillation (p = 0.0083), increasing cerebral atrophy score (p = 0.0001), absence of hyperlipemia (p = 0.0003) and absence of alcohol consumption higher than 300 g/week (p = 0.0398).

CONCLUSION

Our findings do not support the hypothesis that, in stroke patients, LA share similar risk factors than small-vessel disease; other cerebrovascular risk factors may also contribute to LA, perhaps because of decreased cerebral blood flow.