Frontotemporal Dementia (FTD)
The majority of patients with FTD develop the condition in the presenium, with the onset usually occurring between 45 and 60 years of age. About 50% of patients have a positive family history in a first-degree relative. An abnormality of chromosome 17 was present in affected members of a family with an autosomal dominant form of the disease. The incidence of FTD in relation to presenile AD is estimated to be at least 1 : 5. FTD comprises three core clinical dementia syndromes, a behavioural and dysexecutive (or frontal) variant called frontotemporal lobar dementia and two forms of primary progressive aphasia, a temporal lobe variant, also called semantic dementia (SD), and a progressive nonfluent aphasia (PA). The diagnosis of each of these FTLD clinical syndromes relies mainly on the combination of progressive behavioural and neuropsychological impairments and the exclusion of others.
Studies of saccades in FTD have found normal reflexive saccades, but impairment in the ability to inhibit a reflexive saccade in the antisaccade task, that is, impaired reflexive saccade inhibition, except in the SD group.[29,30] However, they were able to self-correct the antisaccade errors as well as controls, in contrast to patients with AD, corticobasal degeneration (CBD), and PSP. Interestingly there was a positive correlation between antisaccade performance and the volume of a segment of the right frontal eye field using an unbiased voxel-based morphometric analysis of grey matter volume in their structural MRI images. Findings in a recent study have shown that saccades are abnormal in FTD, reflecting reduced decision-making speed, and that these abnormalities related to atrophy of the left frontal eye field. In addition, patients with FTD had an increased incidence of early saccades, which may be due to reduced inhibition of primitive responses.
Although FTLD, CBD, and PSP might present with similar pathology, they do represent distinct syndromes. The results of the ocular motor studies so far suggest that saccadic analysis may be useful in differentiating these groups (saccadic gain and velocity, and antisaccade performance).[19,33]
Eye. 2015;29(2):200-207. © 2015 Nature Publishing Group