Reduced sample sizes for atrophy outcomes in Alzheimer's disease trials: baseline adjustment.

Document Type

Article

Abstract

Cerebral atrophy rate is increasingly used as an outcome measure for Alzheimer's disease (AD) trials. We used the Alzheimer's disease Neuroimaging initiative (ADNI) dataset to assess if adjusting for baseline characteristics can reduce sample sizes. Controls (n = 199), patients with mild cognitive impairment (MCI) (n = 334) and AD (n = 144) had two MRI scans, 1-year apart; approximately 55% had baseline CSF tau, p-tau, and Abeta1-42. Whole brain (KN-BSI) and hippocampal (HMAPS-HBSI) atrophy rate, and ventricular expansion (VBSI) were calculated for each group; numbers required to power a placebo-controlled trial were estimated. Sample sizes per arm (80% power, 25% absolute rate reduction) for AD were (95% CI): brain atrophy = 81 (64,109), hippocampal atrophy = 88 (68,119), ventricular expansion = 118 (92,157); and for MCI: brain atrophy = 149 (122,188), hippocampal atrophy = 201 (160,262), ventricular expansion = 234 (191,295). To detect a 25% reduction relative to normal aging required increased sample sizes approximately 3-fold (AD), and approximately 5-fold (MCI). Disease severity and Abeta1-42 contributed significantly to atrophy rate variability. Adjusting for 11 predefined covariates reduced sample sizes by up to 30%. Treatment trials in AD should consider the effects of normal aging; adjusting for baseline characteristics can significantly reduce required sample sizes.

Medical Subject Headings

Aged; Aged, 80 and over; Alzheimer Disease; Atrophy; Brain; Cerebral Ventricles; Cognition Disorders; Female; Hippocampus; Humans; Magnetic Resonance Imaging; Male; Randomized Controlled Trials as Topic; Sample Size; Treatment Outcome

Publication Date

8-1-2010

Publication Title

Neurobiology of aging

ISSN

1558-1497

Volume

31

Issue

8

First Page

1452

Last Page

1462

PubMed ID

20620665

Digital Object Identifier (DOI)

10.1016/j.neurobiolaging.2010.04.011

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