Progressive medial temporal lobe changes in Alzheimer's disease revealed by quantitative MRI: potential use for monitoring of drug-related changes

Reduced cerebral glucose metabolism in patients at risk for Alzheimer's disease

While significantly reduced glucose metabolism in fronto-temporo-parietal and cingulate cortices has been demonstrated in Alzheimer's disease (AD) compared with controls, cerebral glucose metabolism in patients with mild cognitive impairment who subsequently develop AD is less well-defined. In the present study we measured cerebral glucose metabolism by positron emission tomography (PET) with (18)F-2-fluoro-2-deoxy-D-glucose in 14 patients with aging-associated cognitive decline (AACD), 44 patients with AD, and 14 healthy control subjects at baseline. The AACD patients were clinically followed up, and conversion to AD was determined. Compared with controls, AACD patients had significantly reduced glucose metabolism in the right precuneus, posterior cingulate, right angular gyrus, and bilateral middle temporal cortices, while the respective deficits were more pronounced in AD patients and also involved the frontal cortices. AACD patients who subsequently converted to AD (AACD-converters) showed more extended metabolic changes which also involved the frontal and temporal cortices, right cingulate gyrus, right thalamus, and bilateral precuneus.

CSF tau protein and FDG PET in patients with aging-associated cognitive decline and Alzheimer's disease

INTRODUCTION

In Alzheimer's disease (AD), accelerated neurofibrillary tangle formation occurs which is associated with increased tau protein release into the cerebrospinal fluid (CSF). Recent studies found significantly increased CSF tau already in patients at risk of developing AD, indicating its potential as a biochemical marker of AD. Cerebral glucose metabolism is reduced in frontotemporoparietal and cingulate cortices in patients with mild AD. However, few studies have investigated CSF tau protein and cerebral glucose metabolism changes in patients at risk to develop AD.

METHODS

48 patients with AD, 88 patients with aging-associated cognitive decline (AACD), and 39 healthy controls were included. In all participants, CSF levels of tau were determined by ELISA at baseline and compared between the diagnostic groups. 14 AACD patients and 14 controls underwent (18)F-fluorodeoxyglucose positron emission tomography (FDG PET).

RESULTS

AD patients showed the highest CSF tau levels compared with AACD patients and controls. AACD patients had significantly higher tau levels than the controls but lower than the AD patients. AACD patients were characterized by reduced glucose metabolism in bilateral middle temporal cortex, left posterior cingulate cortex, right angular gyrus, and right precuneus compared with controls.

CONCLUSION

In conclusion, our findings reflect and confirm the clinical judgment of an incipient neurodegenerative disorder in a considerable portion of AACD patients. In patients with AACD, CSF tau levels and cerebral glucose metabolism show an altered pattern comparable with that found in AD and thus may facilitate early diagnosis.

Parahippocampal volume deficits in subjects with aging-associated cognitive decline

OBJECTIVE

Neuropathological evidence suggests that the earliest changes in Alzheimer's disease selectively affect the parahippocampal regions of the brain. This study was conducted to determine if otherwise healthy elderly subjects with mild cognitive impairment had structural volume deficits affecting the parahippocampal gyrus.

METHOD

Magnetic resonance imaging (MRI) was used to compare global and regional brain volumes in 21 subjects with mild cognitive deficits defined according to the criteria for aging-associated cognitive decline, 22 cognitively intact comparison subjects, and 12 patients with Alzheimer's disease.

RESULTS

Compared with the cognitively intact subjects, the subjects with aging-associated cognitive decline had a significantly smaller mean volume of the right parahippocampal gyrus. The subjects with aging-associated cognitive decline had a mean parahippocampal volume that was intermediate between that of the Alzheimer's disease patients and that of the cognitively intact subjects.

CONCLUSIONS

Parahippocampal atrophy underlies the observed cognitive deficits in aging-associated cognitive decline. These findings support the hypothesis that aging-associated cognitive decline represents a preclinical stage of Alzheimer's disease.