Neuropathological spectrum of frontal lobe dementias.

Frontotemporal dementia (FTD) is characterized by different severity of frontotemporal atrophy, and histologically by neuronal loss, gliosis and spongiosis. Due to the new discoveries in biochemistry,genetics and neuropathology, re-examination of the former neuropathological criteria was necessary.Actually, we distinguish subgroups on the basis of the presence or absence of intraneuronal or intraneuronal and glial inclusions: the so-called FTD tauopathies, such as Pick's disease, corticobasal degeneration, progressive supranuclear palsy, FTD with parkinsonism linked to chromosome 17,argyrophilic grain disease and neurofibrillary tangle dementia. FTD nontauopathies include dementia lacking distinctive histology (without any known inclusion) and FTD (clinically with or without motor neuron disease) with ubiquitin-immunoreactive inclusions. In the latter group, a new pathological protein, the TAR-binding protein (TDP-43), was recently described as the main component of inclusion, and several new mutations were also discovered. The new neuropathological criteria could be a great help in the neuropathological diagnosis and in further clinicopathological studies, and the new discoveries are useful in understanding the underlying disease processes.