Frontotemporal lobar degeneration insights from neuropsychology and neuroimaging

Frontotemporal lobar degeneration (FTLD) is a diagnostic term that encompasses three distinctly different syndromes, united by historic as well as pathologic commonalities. We briefly review the origins of the current classification scheme for diagnosing the three major subtypes--frontotemporal dementia, semantic dementia, and primary progressive aphasia, highlighting the differences between subtypes as well as from Alzheimer's disease (AD). We briefly examine current understanding regarding the histopathology and genetics of FTLD but note that there is a poor correspondence of these features with specific subtypes of FTLD. For clinicians and clinical researchers, this implicates the need for other diagnostic strategies. Neuropsychological and neurobehavioral testing currently offers the most sensitive and specific method for identifying subtypes, and discriminating FTLD from other forms of dementia. Multiple studies from the relevant literature are reviewed, highlighting those findings that are likely to be most valuable to physicians. Finally, we analyze some of the major findings from the large body of work on neuroimaging of FTLD, again focusing on those studies that potentially help discriminate FTLD subtypes or assist with the discrimination of FTLD from AD.