Quantitative and qualitative features of executive dysfunction in frontotemporal and Alzheimer's dementia

Behavioral variant fronto-temporal degeneration (bvFTD) is typically distinguished from Alzheimer's disease (AD) by early, prominent dysexecutive findings, in addition to other clinical features. However, differences in executive functioning between these groups are not consistently found. The current study sought to investigate quantitative and qualitative differences in executive functioning between those with bvFTD and AD in a large sample, while controlling for dementia severity and demographic variables. Secondary data analyses were completed on a subset of cases from the National Alzheimer's Coordinating Center collected from 36 Alzheimer's Disease Research Centers and consisting of 1,577 individuals with AD and 406 individuals with bvFTD. Groups were compared on 1) ability to complete three commonly administered executive tasks (letter fluency, Trail Making Test Part B [TMTB], and digits backward); 2) quantitative test performance; and 3) errors on these tasks. Findings suggested that individuals with bvFTD were less likely to complete letter fluency, χ(2) = 178.62, p < .001, and number span tasks, χ(1) = 11.49, p < .001), whereas individuals with AD were less likely to complete TMTB, χ(2) = 460.38, p < .001. Individuals with bvFTD performed more poorly on letter fluency, F(1) = 28.06, p = .013, but there were not group differences in TMTB lines per second or number span backwards. Errors generally did not differentiate the diagnostic groups. In summary, there is substantial overlap in executive dysfunction between those with bvFTD and AD, though individuals with bvFTD tend to demonstrate worse letter fluency performance.