Frontotemporal dementia (FTD) describes a group of syndromes caused by pathological processes predominantly affecting the frontal and temporal lobes. It represents the most frequent cause of non-AD degenerative dementia and has been increasingly recognized as an important cause of early-onset dementia.
At least three major anatomic variants of FTD can be described: a bifrontal, slightly asymmetric subtype with more involvement of the right frontotemporal region (frontal variant), a temporal-predominant subtype (temporal variant or semantic dementia), and a left frontal-predominant subtype (progressive nonfluent aphasia). There is clinical and pathological overlap between the syndromes and the influence of genetic factors varies substantially across the syndromes.
Symptoms can be generally related to impairment of functions of the affected brain regions, with behavioral symptoms and deficits in executive functions. Extensive loss of pyramidal neurons in the frontotemporal cortex, severe gliosis within the gray and white matter, and presence of Pick bodies are the most common histologic findings.
Structural MRI scans frequently reveal frontal lobe and/or anterior temporal lobe atrophy, often with significant asymmetry. When advanced volumetric techniques such as voxel-based morphometry are used, brain atrophy in the different types of FTD seem to be closely correlated to the cerebral location responsible for the clinical syndrome. It has been suggested that it may be possible to differentiate autopsy-proven FTD from AD on the basis of the brain atrophy pattern. However, at the earliest disease stages, the differential diagnosis between dementia types is difficult, even using quantitative neuroimaging techniques.

1H-MRS

The metabolite changes of FTD patients are very similar to those seen in AD. Usually, NAA/Cr is lower than in normal controls and mI/Cr is higher. However, accurate regional 1H-MRS measurements may help to differentiate dementias that display regionally specific involvement such as FTD. This may be particularly important at the early stages of disease progression, as these regional differences may disappear at later stages when the neurodegenerative pathology becomes more widespread and involves the majority of the cerebral cortex.