Frontotemporal dementia with right temporal predominance: a clinical comparison with left-predominant FTD

The right-temporal variant of frontotemporal dementia (FTD) is well characterised. Whether it should be considered a distinct clinical entity, separate from other syndromes of FTD, remains an open question. The study addressed the issue through a retrospective comparison of clinical characteristics of patients with predominant atrophy in right or left anterior temporal lobe (R-ATL vs. L-ATL).

Patients were identified from a clinical database, diagnosed with FTD, and reported to show temporal lobe atrophy on imaging. Fifty-one patients were selected in whom independent ratings of atrophy were greatest in right or left anterior temporal lobe. Presenting symptoms, cognitive and behavioural characteristics, neuropsychological findings, and diagnostic classification were recorded.

Difficulty recognising people, impaired decision-making, perseverative preoccupations, disinhibition, and loss of empathy characterised the R-ATL group, in keeping with the previous reports. There was, however, overlap in cognitive and behavioural symptomatology in R-ATL and L-ATL, and sensitivity and specificity values were modest. Group differences diminished with disease progression. The most common clinical classification at first assessment in both groups was semantic dementia (SD), with other patients being classified as behavioural-variant FTD (bvFTD), FTD with amyotrophic lateral sclerosis or mixed FTD/SD. Not all patients with L-ATL met criteria for semantic variant primary progressive aphasia (svPPA).

The data question the notion that R-ATL and L-ATL presentations are separate entities. We argue that a common diagnostic framework for the two is warranted, with classification being based on cognitive/behavioural characteristics rather than neuroradiological grounds.