Objective
To examine the utility of single photon emission computed tomography (SPECT) to predict conversion from mild cognitive impairment (MCI) to Alzheimer's disease (AD).
Design
Longitudinal, prospective study.
Setting
University-based memory disorders clinic.
Participants
127 patients with MCI and 59 healthy comparison subjects followed for 1 to 9 years.
Measurements
Diagnostic evaluation, neuropsychological tests, social/cognitive function, olfactory identification, apolipoprotein E genotype, MRI, and brain 99mTc HMPAO SPECT scan with visual ratings and region of interest (ROI) analyses were done.
Results
Visual ratings of SPECT temporal and parietal blood flow did not distinguish eventual MCI converters to AD (n=31) from non-converters (n=96) but the global rating predicted conversion (41.9% sensitivity and 82.3% specificity, Fisher's exact test p=0.013). Blood flow in each ROI was not predictive, but when dichotomized at the MCI patients' median value, low flow increased the hazard of conversion to AD for parietal (HR 2.96, 95%CI 1.16-7.53, p=0.023) and medial temporal regions (HR 3.12, 95%CI 1.14-8.56, p=0.027). In the 3-year follow-up sample, low parietal (p<0.05) and medial temporal (p<0.01) flow predicted conversion to AD, with or without controlling for age, MMSE, and apolipoprotein E ε4 genotype. These measures lost significance when other strong predictors were included in logistic regression analyses: verbal memory, social/cognitive functioning, olfactory identification deficits, hippocampal and entorhinal cortex volumes.
Conclusions
SPECT visual ratings showed limited utility in predicting MCI conversion to AD. The modest predictive utility of quantified low parietal and medial temporal flow using SPECT may decrease when other stronger predictors are available.