INTELLECTUAL DECLINE PREDICTS THE PARIETAL PERFUSION DEFICIT IN ALZHEIMERS-DISEASE

The pathophysiology of Alzheimer's disease may be reflected more in an individual's decline from premorbid levels of functioning than in cur rent measures of absolute severity. To test this hypothesis, we comput ed an index of intellectual decline for individual patients and examin ed its relationship to Alzheimer's disease-related functional brain ab normalities. Methods: We studied 27 patients with Alzheimer's disease diagnosed by ADRDA-NINCDS criteria. We used patient demographics and p ublished formulas to construct estimates of premorbid Wechsler Adult I ntelligence Scale (WAIS-R) IQs for each subject in the sample and used a current IQ assessment to estimate the decline in IQ that occurred d uring the disease for each subject. Cortical perfusion was quantified by the planar Xe-133 regional cerebral blood flow (rCBF) technique. Th e characteristic abnormality in parietal cortex was expressed by the p arietal index (PI). Results: Over the estimated disease duration of 3. 8 +/- 2.2 yr, the full-scaled IQ declined by an estimated 28.0 +/- 15. 5 points. The current PI was in turn well correlated with the IQ decli ne (r = 0.66; p < 0.001). This association was linear and stronger tha n those with other, more common measures of current severity. A multip le stepwise regression analysis suggested that IQ decline alone accoun ted for the variance in PI related to clinical deterioration. Actual i mages showed a mild blood flow deficit in patients with the smallest e stimated IQ declines but deep and extensive lesions in patients with l arge declines. Conclusion: These results suggest that the decline from the premorbid baseline, rather than current level of functioning, bes t predicts the extent of brain damage reflected in the rCBF abnormalit y, a finding independent of demographic variance.