Decreased medial temporal oxygen metabolism in Alzheimer's disease shown by PET

In mild-to-moderate Alzheimer's disease, previous PET studies failed to reveal significant involvement in the medial temporal lobe having pathologically neurodegenerative changes. The purpose of this study was to clarify the medial temporal perfusion and functional changes in mild-to-moderate Alzheimer's disease using PET. Methods: Sixteen patients with probable mild-to-moderate Alzheimer's disease (age 62.9 +/- 6.0 yr, MMSE 17.7 +/- 3.7) and 14 normal volunteers (age 60.9 +/- 5.9 yr) were studied. Regional cerebral blood flow (CBF), oxygen metabolism (CMRO(2)) and oxygen extraction fraction (OEF) were measured using O-15 steady-state method and PET. By rendering magnetic resonance volumetry of the medial temporal structures, the significance of partial volume effects on PET study measurements was examined. Results: The mean CMRO(2) in the medial temporal, as well as in the parietal and lateral temporal cortices were significantly lower in the patient group than in the control group. The mean CBF in the parietal and lateral temporal cortices also significantly decreased in the patient group. The OEF in the medial temporal was also decreased in the Alzheimer's disease group, while the OEF in the other cortical regions in Alzheimer's disease group were similar to that of control group. Decline of medial temporal oxygen consumption was the most distinctive feature of Alzheimer's disease. Those measurements were independent from volume of medial temporal structures. In Alzheimer's disease, medial temporal CMRO(2) and CBF correlated with some of the nonverbal memory test scores and cognitive impairment scales, when normalized for individual difference. Conclusion: Medial temporal oxygen metabolism was markedly affected in patients with mild-to-moderate Alzheimer's disease. This measure substantiated the functional impairment of the medial temporal region in Alzheimer's disease.