016 One disease or three: is frontotemporal dementia – motor neuron disease a distinct entity?

Abstract

IntroductionFrontotemporal dementia-motor neuron disease (FTD-MND) is diagnosed when patients meet criteria for the diagnosis of both FTD and MND, but the mode presentation of this disorder is currently unknown. This study aimed to compare the mode of presentation, and profiles of behavioural and language disturbances, of FTD-MND with that of other FTD phenotypes using a data-driven approach.Methods31 FTD-MND, 119 bvFTD, 47 PNFA, 42 SD patients and 127 controls underwent comprehensive clinical, neuropsychological and neuroimaging assessments. Z-transformed scores were used to compare the severity of behavioural and language domains in each disease group. Two-step cluster analysis profiled patient subgroups. Voxel-based morphometry investigated differential patterns of cortical atrophy between groups.ResultsOverall, FTD-MND patients presented with behavioural or language disturbances less frequently than FTD phenotypes, but mixed behavioural-language presentations were more common. FTD-MND patients demonstrated less severe disinhibition, apathy and semantic deficits relative to bvFTD and SD respectively.Behavioural and language deficits were of comparable severity in FTD-MND, unlike other FTD phenotypes where behaviour was worse than language (bvFTD) or language worse than behaviour (PNFA, SD).In cluster analysis, FTD-MND patients were evenly distributed across three subgroups designated as ‘mild mixed’, ‘language dominant’ and ‘behavioural dominant’. Relative to the ‘mild mixed’ group, ‘language dominant’ patients demonstarted more atrophy of the anterior temporal lobe and peri-insular regions, while ‘behavioural dominant’ patients displayed more prefrontal atrophy.ConclusionFTD-MND does not present as a uniform syndrome. Rather, there may be at least three subgroups that demonstrate distinctive cognitive, behavioural, and neuroanatomical characteristics.