Visuospatial dysfunction in Alzheimer's disease and behavioural variant frontotemporal dementia

Objectives Approximately 30% of Alzheimer's disease (AD) patients are misdiagnosed due to overlapping and evolving clinical features. In particular, the distinction of AD from behavioural variant frontotemporal dementia (bvFTD) can be challenging. Measures of visuospatial ability, which rely on parietal lobe function, show promise as markers of AD as the parietal lobe is preferentially affected early in the disease course. We hypothesise that traditional measures of visuospatial function may help distinguish AD from bvFTD. Materials & methods The Addenbrooke's Cognitive Examination (ACE) visuospatial subtask, Rey-Osterrieth Complex Figure (RCF) task, and subtests of the visual object and space perception battery (VOSP) were used to examine visuospatial abilities in 55 AD patients, 51 bvFTD patients, and 54 healthy Controls. A subgroup analysis was performed in patients with Pittsburgh Compound B positron emission tomography (PiB-PET) data. Results Relative to Controls, AD and bvFTD patients were impaired on almost all visuospatial tasks. Significantly worse performance was observed in AD relative to bvFTD patients on drawing tasks (ACE pentagons/loops copy, cube copy, and all RCF scores) and tasks of spatial orientation (VOSP cube analysis), when controlling for disease severity. Conclusions Visuospatial measures demonstrate limited ability to distinguish between AD and bvFTD unless disease severity is taken into consideration. Controlling for disease severity reveals a disproportionate visuospatial impairment in AD compared to bvFTD. Development of targeted measures of visuospatial function is required to improve differential diagnosis of these syndromes.