The ratio of mesial to neocortical temporal lobe blood flow as a predictor of dementia

OBJECTIVE: The hypothesis tested was that an increased ratio of cerebral blood flow (rCBF) in the mesocortical temporal lobe to that of the neocortical temporal lobe (MES/NEO ratio) would be related to clinical measures of dementia severity and would help distinguish Alzheimer's patients from normal controls. DESIGN: The rCBF of nine Alzheimer's patients (5 males and 4 females; age = 65.9 +/- 6.0 years, range 55-71; Folstein Mini-Mental Status Examination = 18.6 +/- 7.4, range 9-28) and 10 age-matched normal controls (7 males, 3 females; age = 66.0 +/- 5.7 years, range 58-75) was determined by positron emission tomography (PET) using H(2)15O and the method of Alpert et al.(25) RESULTS: Alzheimer's disease patients had a significantly higher MES/NEO ratio (1.19 +/- .17) than the age-matched normal controls (.854 +/- 14; t = .-4.74, df = 17, P =.0002). Using a MES/NEO ratio of 1 as the cutoff point for discrimination between Alzheimer's patients and normal controls, the ratio demonstrated 100% sensitivity (no. of correctly identified Alzheimer's patients/no. of Alzheimer's patients) and 90% specificity (no. of correctly identified unaffected subects/no. of unaffected subjects). Further, those patients with the highest MES/NEO ratios had the lowest overall measures of cognitive function (Folstein Mini-Mental Status Examination: r = -.75, P < .02, 1-tail; Mattis Dementia Rating Scale: r = -0.655, P =.028, 1-tail) scores. CONCLUSIONS: The findings are consistent with other in vivo and postmortem studies, suggesting that functional and structural changes of the lateral temporal lobe in Alzheimer's disease occur relatively early in the disease process and appear to be distinguishable from those changes accompanying normal aging. In contrast, the memory loss and pathology of the mesial temporal lobe that is characteristic of the early stages of Alzheimer's patients do not appear to be associated with a reduction in cerebral blood flow in the resting Alzheimer's patient. Nevertheless, the clinical significance of the results must await findings of longitudinal studies of larger numbers of Alzheimer's patients and controls.