Loss of frontal fMRI activation in early frontotemporal dementia compared to early AD.

Objective: To compare frontal cortex activation in patients with early frontotemporal dementia (FTD) with that in patients with early AD.
Methods: Seven patients with FTD and seven patients with AD were studied (Clinical Dementia Rating: four patients with FTD 0.5, three patients with FTD 1, all patients with AD 1; mean Mini-Mental State Examination score: FTD 28.0 +/- 2.1, AD 23.1 +/- 2.7). Cerebral atrophy on MRI was mild, with no differences between FTD and AD. A parametric working memory task was applied to assess frontal activation as a function of working memory load.
Results: The activated working memory network in FTD and AD included frontal and parietal lobe and thalamus. In frontal and parietal cortex, brain activation was significantly decreased in FTD. Frontal regions in patients with FTD showed less linear activation increase with working memory load than in AD. Possibly as a compensation mechanism, the cerebellum showed a stronger increasing response in FTD.
Conclusions: These data on regional functional loss in the frontal cortex in early FTD suggest that fMRI can identify FTD when results on structural MRI are normal.