Differentiation of semantic dementia and Alzheimer's disease using the Addenbrooke's Cognitive Examination (ACE)

Abstract

Background: The Addenbrooke's Cognitive Examination (ACE) is a simple diagnostic tool bridging the gap between the very brief Mini Mental State Exam (MMSE) and much longer test batteries used by neuropsychologists which has proven extremely popular internationally.

Objective: We aimed to assess the ability of the ACE to differentiate semantic dementia (SD) from Alzheimer's disease (AD).

Methods: The ACE was administered to three groups: SD patients (n = 40) and two separate groups of AD patients (n = 40 in each), matched for overall ACE or MMSE score.

Results: Significant differences were found between SD and both AD groups for the ACE sub-scores of naming, reading and orientation in time. Discriminant analysis (SD versus AD) led to the formulation of a 'semantic index' (naming plus reading minus scores for serial-7s, orientation in time and drawing). Application of the semantic index to the patient data found values of less than zero to be predictive of SD rather than AD with 88% sensitivity and 90% specificity. Validation analysis in an independent sample of 24 SD and AD patients proved even more favourable.

Conclusions: The overall ACE score is known to be a sensitive, and specific, indicator of early neurodegenerative dementia; this study shows that the ACE can also be used to detect SD through application of the semantic index.