Objective: To quantify the regional and global cerebral atrophy rates and assess acceleration rates in healthy controls, subjects with mild cognitive impairment (MCI), and subjects with mild Alzheimer disease (AD).Methods: Using 0-, 6-, 12-, 18-, 24-, and 36-month MRI scans of controls and subjects with MCI and AD from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database, we calculated volume change of whole brain, hippocampus, and ventricles between all pairs of scans using the boundary shift integral.
Results:We found no evidence of acceleration in whole-brain atrophy rates in any group. There was evidence that hippocampal atrophy rates in MCI subjects accelerate by 0.22%/year 2 on average (p 5 0.037). There was evidence of acceleration in rates of ventricular enlargement in subjects with MCI (p 5 0.001) and AD (p , 0.001), with rates estimated to increase by 0.27 mL/year 2 (95% confidence interval 0.12, 0.43) and 0.88 mL/year 2 (95% confidence interval 0.47, 1.29), respectively. A post hoc analysis suggested that the acceleration of hippocampal loss in MCI subjects was mainly driven by the MCI subjects that were observed to progress to clinical AD within 3 years of baseline, with this group showing hippocampal atrophy rate acceleration of 0.50%/year 2 (p 5 0.003).
Conclusions:The small acceleration rates suggest a long period of transition to the pathologic losses seen in clinical AD. The acceleration in hippocampal atrophy rates in MCI subjects in the ADNI seems to be driven by those MCI subjects who concurrently progressed to a clinical diagnosis of AD. Neurology Alzheimer disease (AD) is associated with higher rates of brain tissue loss than normal aging, 1 with the rate in mild cognitive impairment (MCI) falling somewhere in between.2 This implies increases in the rate of tissue loss (i.e., acceleration) as the individual progresses from normal to MCI and then on to dementia due to AD.3,4 A sigmoidal model of tissue loss in AD 5 has been proposed that suggests the rate of tissue loss first accelerates, then remains constant, and finally decelerates; however, detailed data about how the rates of regional and global atrophy change over time are lacking. Assessing how rates of atrophy change in the transition from normal aging through early cognitive impairment and on to dementia due to AD is important for understanding the presymptomatic period of AD, which is increasingly considered as a potential therapeutic window for disease-modification trials.A number of studies have investigated acceleration in regional and global atrophy rates in normal aging, MCI, and clinically diagnosed AD, with most modeling tissue loss as a function of age or time from a particular clinical stage (e.g., at the time of AD dementia diagnosis or Mini-Mental State