Can cognitive assessment really discriminate early stages of Alzheimer's and behavioural variant frontotemporal dementia at initial clinical presentation?

Abstract

Background: Neuropsychological testing is considered crucial for differential diagnosis of Alzheimer's disease (AD) and behavioural variant frontotemporal dementia (bvFTD). In-depth neuropsychological assessment revealed specific dysfunctions in the two dementia syndromes. However, a significant overlap of cognitive impairments exists in early disease stages. We questioned whether a standard neuropsychological assessment at initial clinical presentation can delineate patients with AD versus bvFTD.

Methods: In a retrospective approach, we evaluated and compared how cognitive profiles assessed at initial clinical presentation predicted the diagnosis of later verified AD (n = 43) and bvFTD (n = 26). Additionally, the neuropsychological standard domains memory, language, visuospatial skills, executive functions, praxis and social cognition were subjected to stepwise discriminant analysis to compare their differential contribution to diagnosis.

Results: Regardless of diagnosis, a percentage of patients presented with major deterioration in a wide range of cognitive domains when compared with age-matched normative data. Only few significant differences were detected on the group level: Patients with AD were relatively more impaired in the verbal recall, verbal recognition, figure copy, and surprisingly in the executive subdomains, set shifting and processing speed whereas bvFTD was characterised by more deficits in imitation of face postures. A combination of tests for verbal recall, imitation of limb and face postures, and figure copy showed the greatest discriminatory power.

Conclusions: Our results imply that the contribution of a standard neuropsychological assessment is limited for differential diagnosis of AD and bvFTD at initial presentation. In contrast to current clinical guidelines, executive functions are neither particularly nor exclusively impaired in patients with bvFTD when assessed within a standard clinical neuropsychological test battery. The significant overlap of bvFTD and AD concerning the profile of cognitive impairments questions current neuropsychological diagnostic criteria and calls for revision, regarding both the degree and the profile of cognitive deficits.

Keywords: Alzheimer’s dementia (AD); Behavioural variant frontotemporal dementia (bvFTD); Differential diagnosis; Neuropsychological tests.

Fig. 1

Flowchart illustrating participant selection and exclusion criteria

Fig. 2

Individual test performance of patients with dementia. Percentage of patients with Alzheimer’s disease (AD) (a) and patients with behavioural variant of frontotemporal dementia (bvFTD) (b) with pathological z-scores (less than −1.5 SD) adjusted for sex, age and years of education

Fig. 3

Comparison of cognitive profiles of patients with behavioural variant of frontotemporal dementia (bvFTD) and patients with Alzheimer’s disease (AD). X-axis displays cognitive subdomains, and y-axis displays z-score values. The lines display mean scores for each group in each subdomain. * Significant differences between the groups at a significance level of p < 0.05 for the marked subdomain; ** significant differences between the groups at p < 0.003 (significance level after Bonferroni correction for number of cognitive tests) for the marked subdomain