Age transformation of combined hippocampus and amygdala volume improves diagnostic accuracy in Alzheimer's disease.

Objective: The specificity of magnetic resonance imaging (MRI)-based hippocampal measurements in detecting Alzheimer's disease (AD) pathology is reduced by an age-related reduction of the hippocampus volume. We propose an adjustment for this age effect to increase the diagnostic accuracy of hippocampal volumes in AD.
Method: Using an orthogonal rotational transformation of the coordinate system, values of MRI-determined volumes of hippocampus-amygdala formation (HAF) were transformed according to the age effect in 27 AD patients and 28 age- and sex-matched healthy control subjects.
Results: The age transformation increased the diagnostic accuracy of HAF volumes in the study sample and in an independent sample from the literature. The age-transformed HAF volume predicted AD in a subject with mild cognitive impairment (MCI) with later biopsy-confirmed AD.
Conclusion: Age transformation may provide an easily applicable method to increase the clinical diagnostic accuracy of hippocampal measurements by considering the effect of aging on hippocampus volume.