A clinical-radiological framework of the right temporal variant of frontotemporal dementia

Abstract

The concept of the right temporal variant of frontotemporal dementia (rtvFTD) is still equivocal. The syndrome accompanying predominant right anterior temporal atrophy has previously been described as memory loss, prosopagnosia, getting lost and behavioural changes. Accurate detection is challenging, as the clinical syndrome might be confused with either behavioural variant FTD (bvFTD) or Alzheimer's disease. Furthermore, based on neuroimaging features, the syndrome has been considered a right-sided variant of semantic variant primary progressive aphasia (svPPA). Therefore, we aimed to demarcate the clinical and neuropsychological characteristics of rtvFTD versus svPPA, bvFTD and Alzheimer's disease. Moreover, we aimed to compare its neuroimaging profile against svPPA, which is associated with predominant left anterior temporal atrophy. Of 619 subjects with a clinical diagnosis of frontotemporal dementia or primary progressive aphasia, we included 70 subjects with a negative amyloid status in whom predominant right temporal lobar atrophy was identified based on blinded visual assessment of their initial brain MRI scans. Clinical symptoms were assessed retrospectively and compared with age- and sex-matched patients with svPPA (n = 70), bvFTD (n = 70) and Alzheimer's disease (n = 70). Prosopagnosia, episodic memory impairment and behavioural changes such as disinhibition, apathy, compulsiveness and loss of empathy were the most common initial symptoms, whereas during the disease course, patients developed language problems such as word-finding difficulties and anomia. Distinctive symptoms of rtvFTD compared to the other groups included depression, somatic complaints, and motor/mental slowness. Aside from right temporal atrophy, the imaging pattern showed volume loss of the right ventral frontal area and the left temporal lobe, which represented a close mirror image of svPPA. Atrophy of the bilateral temporal poles and the fusiform gyrus were associated with prosopagnosia in rtvFTD. Our results highlight that rtvFTD has a unique clinical presentation. Since current diagnostic criteria do not cover specific symptoms of the rtvFTD, we propose a diagnostic tree to be used to define diagnostic criteria and call for an international validation.