Purpose The diagnosis of behavioural variant frontotemporal
dementia (bvFTD) is challenging during the predementia
stage when symptoms are subtle and confounding.
Morphological and functional neuroimaging can be particularly
helpful during this stage but few data are available.
Methods We retrospectively selected 25 patients with lateonset
probable bvFTD. Brain structural MRI and FDG PET
were performed during the predementia stage (mean MMSE
score 27.1± 2.5) on average 2 years before. The findings with
the two imaging modalities were compared (SPM8) with
those in a group of 20 healthy subjects. The bvFTD patients
were divided into two subgroups: those with predominant
disinhibition (bvFTD+) and those with apathy (bvFTD-).
Results Hypometabolism exceeded grey matter (GM) density
reduction in terms of both extension and statistical significance
in all comparisons. In the whole bvFTD group,
hypometabolism involved the bilateral medial, inferior and
superior lateral frontal cortex, anterior cingulate, left temporal
and right parietal cortices and the caudate nuclei. GM density
reduction was limited to the right frontal cortex and the left
medial temporal lobe. In bvFTD+ patients hypometabolism
was found in the bilateral medial and basal frontal cortex,
while GM reduction involved the left anterior cingulate and
left inferior frontal cortices, and the right insula. In bvFTD-
patients, atrophy and mainly hypometabolism involved the
lateral frontal cortex and the inferior parietal lobule.
Conclusion These findings suggest that hypometabolism is
more extensive than, and thus probably precedes, atrophy in
predementia late-onset bvFTD, underscoring different topographic
involvement in disinhibited and apathetic presentations.
If confirmed in a larger series, these results should
prompt biomarker operationalization in bvFTD, especially
for patient selection in therapeutic clinical trials.
