Preservation of reasoning in Primary Progressive Aphasia: Further differentiation from Alzheimer's disease and the behavioral presentation of frontotemporal dementia

Abstract

Primary Progressive Aphasia (PPA) is a clinical dementia syndrome characterized by the gradual dissolution of language without impairment of other cognitive domains for at least the first 2 years of illness (M.-M. Mesulam, 1982, 2001). It is difficult to demonstrate the integrity of nonlanguage domains in PPA because most neuropsychological tests of memory, reasoning, and attention require language competence for their performance. In the present study, reasoning and cognitive flexibility were tested nonverbally in patients with PPA using a modified ten-item version of the Visual Verbal Test (Feldman & Drasgow, 1959). This test measures the ability to detect similarities among objects and to sort a single set of objects according to two different principles. The performance of PPA patients (n = 20) was compared with that of patients with dementia of the Alzheimer type (AD) (n = 20), patients with the comportmental/executive dysfunction variant of frontotemporal dementia (FTD) (n = 16), and cognitively intact controls (n = 20). Patients with PPA and controls performed similarly, detecting commonalities among objects and shifting from one sorting principle to another. In contrast, both AD and FTD subjects were significantly impaired on both measures. These results provide evidence of preserved reasoning in PPA, further differentiating this syndrome from other behaviorally focal dementia syndromes.