Participants
On hundred eighty four participants (41 cognitively healthy individuals (CHI) and 143 demented individuals (DI)) were included in this case control design study between January 2009 and December 2009, after obtaining their informed consent or the agreement of the trusted person, as appropriate. Consent forms were acquired from all participants sent for a memory complaint by their primary care physician to the memory clinic of Angers University Hospital, France. The eligible criteria for inclusion in this study were age 65 and over, ambulatory, adequate ability to understand and speak French and no acute medical illness in the past month. The exclusion criteria were active depression and mild cognitive impairment. The classification of normal cognition and dementia were determined at a weekly interdisciplinary conference based on the neuropsychological and behavioural tests performance, as well as physical examination findings, blood values and brain imaging findings. The diagnosis of dementia followed the Diagnostic and statistical manual of mental disorders fourth edition (DSM-IV) criteria [4]. Alzheimer's disease (AD) and vascular dementia were diagnosed according to respectively the NINCDS-ADRDA criteria for probable AD and the criteria of the DSM-IV [5, 6]. This study was in accordance with the ethical standards set forth in the declaration of Helsinki (1983). The local ethics committee of Angers University Hospital (Committee for the Protection of People West-2, Angers, France) approved the project.
Neuropsychological evaluation
Neuropsychological evaluation was performed during a face-to-face examination carried out by a neuropsychologist. The following standardized tests were used to probe several aspects of cognitive function: the MMSE [4], the Cognitive Assessment Battery (CAB) [7], the Frontal Assessment Battery (FAB) [8], and the Instrumental Activities of Daily Living (IADL) [9]. The CAB assesses cognitive function as a whole (i.e., memory, language, praxia, spatiotemporal orientation and reasoning). It is composed of 96 items and its completion time is around 45 minutes. Score range varies from 0 to 96, with 96 indicating a normal cognitive functioning [7]. The FAB is a validated, short bedside questionnaire designed to assess both cognitive and behavioural changes in frontal lobe dysfunctions [8]. The FAB is a scale composed of 6 subtests (conceptualization, mental shifting, motor programming, sensitivity to interference, inhibitory control, and environment autonomy). It can be performed in approximately 10 minutes. Score range varies from 0 to 18, a score of 18 indicating normal executive functioning [8]. The IADL is a scale evaluating the autonomy to perform the instrumental activities of daily living (i.e., using transportation, managing finances, using the phone, managing medicines) [9]. Each affected function is marked 0. Score range varies from 0 to 4, a score under 3 indicating disability [9].
The SMMSE score was built from the 6 memory items of the MMSE. It was calculated following the formula: [immediate recall of 3 words + delayed recall of 3 words]. The score ranged from 0 to 6, with 6 indicating the best performance.
Statistics
The participants' baseline characteristics were summarized using means and standard deviations or frequencies and percentages, as appropriate. Participants were separated into two groups: CHI and DI. Comparisons between groups were performed using t-test for independent samples or Chi-square, as appropriate. Uni and multiple logistic regression analyses were performed to specify the association between dementia (dependent variable) and SMMSE (independent variable) adjusted on baseline characteristics. Sensitivity analysis consisted of building a receiver operator curve (ROC) by computing the sensitivity and specificity of each SMMSE score (from 0 to 6), to determine the most discriminated threshold maximizing both sensitivity and specificity (Figure 1). Sensitivity, specificity, PPV, negative predictive value (NPV), positive and negative likehood ratio (LR), and odds ratio (OR) for dementia were calculated for the SMMSE based on the cut-off value determined by the sensitive analysis, and for the MMSE based on the cut-off value ≤ 24 [1–3]. P-values < 0.05 were considered as statistically significant. All statistics were performed using SPSS (version17.0; SPSS, Inc., Chicago, IL) and Dag-stat a spreadsheet for the calculation of comprehensive statistics for the assessment of diagnostic tests [10].