Identification of clinical subtypes of fronto-temporal dementia and cerebral blood flow on SPECT: preliminary results

Clinical manifestations and lesional topography indicate that fronto-tempor al dementia (FTD) is a heterogeneous disorder. The aim of this study is to establish a relationship between behavioural profiles and patterns of hypop erfusion in the anatomo-functional systems of the prefrontal cortex. The in itial behavioural characteristics of 12 patients with FTD according to Lund and Manchester criteria were analysed in order to separate patients into s ubgroups. Two groups with different clinical profiles were identified: one group with signs of behavioural disinhibition (the moriatic group) and anot her group with signs of social withdrawal (the apragmatic group). Regions o f interest in ventral and dorsal prefrontal regions and four regions outsid e the frontal lobe were manually drawn on axial HMPAO-SPECT images. In the moriatic group, regional cerebral blood flow (rCBF) was reduced in the vent ral orbitofrontal cortex and the caudate nucleus, contrasting with a decrea se of rCBF in the dorsal medial prefrontal cortex, and especially the left hemisphere, in the apragmatic group. For both groups, there was a marked re duction of rCBF in the anterior temporal cortex compared with control subje cts. The patterns of hypoperfusion in the two groups indicate that differen t behavioural syndromes of FTD result from preferential involvement of dist inct neural systems of the prefrontal cortex: the moriatic subtype of FTD m ay be related to preferential involvement of the ventral prefrontal system, while the apragmatic subtype of FTD may be related to preferential involve ment of the dorsal prefrontal system.