We compared the cognitive profile of patients who fulfill current diagnostic criteria of AD (N = 43) and bvFTD (N = 30) and provide additional biomarker evidence of the underlying pathological process. Differential test performances in standard clinical tests for the domains memory, language, visuospatial skills, executive functions, praxis and emotion recognition were submitted into a stepwise discriminant analysis.
Compared with normative sample data, both patients groups showed deterioration in all cognitive domains. Patients with AD were significantly more impaired in the domains episodic memory and visuospatial skills than patients with bvFTD. AD patients also scored lower in the subdomains processing speed, set shifting, limb imitation and pantomime of object use. Patients with bvFTD had a significantly lower performance in imitation of face postures. For successful group classification in 86.3% of our cases, the subdomains verbal short term memory, imitation of face postures, imitation of limb gestures and figure copy task were selected by a stepwise discriminant analysis. Subsequent jackknifed cross-validation of the test selection led to an accuracy of 79.5% to discriminate between the two groups.
Given that global cognitive impairment is present in patients with bvFTD as well as in patients with AD, standardized neuropsychological assessment is essential to assess the degree and profile of cognitive dysfunctions for clinical diagnosis. A test battery consisting of a memory retrieval task, a figure copy task and an apraxia tasks for limb and face imitation correctly classifies between patients with AD and bvFTD in 79.5% and supports differential diagnosis. Tests on executive function and emotion recognition are not useful to distinguish between the dementia syndromes when only assessed through standard tests without more specific and detailed assessments.