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NEUROLOGY 2007;69:133-139
© 2007 American Academy of Neurology

A plateau in pre-Alzheimer memory decline

Evidence for compensatory mechanisms?

G. E. Smith, PhD, V. S. Pankratz, PhD, S. Negash, PhD, M. M. Machulda, PhD, R. C. Petersen, MD, PhD, B. F. Boeve, MD, D. S. Knopman, MD, J. A. Lucas, PhD, T. J. Ferman, PhD, N. Graff-Radford, MD and R. J. Ivnik, MD, PhD

From the Departments of Psychiatry and Psychology (G.E.S., M.M.M., J.A.L., T.J.F., R.J.I.) and Neurology (S.N., R.C.P., B.F.B., D.S.K., N.G.-R.) and Division of Biostatistics (V.S.P.), Mayo Clinic-Rochester (G.E.S., V.S.P., S.N., M.M., R.C.P., B.F.B., D.S.K., R.J.I.), MN, and Mayo Clinic-Jacksonville (J.A.L., T.G.F., N.G.-R.), FL.

Address correspondence and reprint requests to Dr Smith, Department of Psychiatry and Psychology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905 smith.glenn{at}mayo.edu

Objective: To compare logistic and bilogistic models to describe the pattern of cognitive decline in the preclinical phase of Alzheimer disease (AD).

Methods: We conducted mixed effects modeling of Mayo Cognitive Factors Scores to determine the longitudinal pattern of cognitive decline in the period 10 years prior to and 5 years following a clinical diagnosis of AD. Our analysis included 199 people that eventually received a diagnosis of clinically probable AD. Participants had at least two neuropsychological evaluations including one before the evaluation at which they received the AD diagnosis.

Results: A bilogistic model, including terms for a plateau in the course of cognitive decline, better fit longitudinal memory scores than a simple logistic model. On average the plateau began about 4 years prior to the clinical diagnosis of AD and ended with a decline that probably contributed to the clinical diagnosis of AD. A similar plateau was not evident in four other cognitive domains.

Conclusions: The current findings may support proposed compensatory hypotheses involving redundant memory systems, up-regulation of neurotransmitters, or recruitment of other neural networks.

Supplemental data at www.neurology.org

Supported in part by the Robert H. and Clarice Smith and Abigail Van Buren Alzheimer's Disease Research Program of the Mayo Foundation and National Institute on Aging grants P50 AG16574, UO1 AG06786, RO1 AG15866.

Disclosure: The authors report no conflicts of interest.

Received December 7, 2006. Accepted in final form February 28, 2007.




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Pre-AD Decline: A Linear Progression?
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