Right Temporal Lobe Variant of Frontotemporal Dementia

Abstract

Frontotemporal dementia corresponds to a heterogenous group of syndromes characterized by progressive changes in behavior and/or language. Approximately 30% of patients with primary progressive aphasia, semantic variant (semantic dementia), present with atrophy in the right cerebral hemisphere, in a rare clinical condition called right temporal variant of frontotemporal dementia (rtvFTD). The objective of the study is to present the main demographic, clinical, neuropsychological, neuroimaging, and pathologic characteristics of rtvFTD patients. A systematic review of the literature was carried out in the PubMed, LILACS, and SCIELO databases between January and March 2022. After the evaluation process, 41 articles were selected, published between 1993 and 2021. We found that rtvFTD presents with severe and progressive prosopagnosia (related to anterior temporal lobe injury) associated with behavioral symptoms—desinibition (51%), apathy (39%), obsessive-compulsive symptoms (37%), changes in eating habits (33%), and depression (28%), which is different from semantic dementia. The most common pathologic pattern is TDP-43, type C. This field of knowledge has few studies (mainly reports and case series) and heterogenous nomenclature, which is a limitation. A multinational longitudinal registry of people with rtvFTD, with standardized assessment and description of symptoms, is necessary to elucidate the characteristics of this entity.

Longitudinal volumetric changes in amygdala subregions in frontotemporal dementia

“…Another possible limitation is our explicit decision to exclude patients with right-lateralized SD, which presents with extensive atrophy in the right temporal lobes, given their small number. Whether the severity and trajectory of amygdala changes in this group mirror those seen in the typical left-lateralized SD will be important to investigate, particularly in light of the renewed interest in this syndrome [ 60 , 61 ].…”

The problematic syndrome of right temporal lobe atrophy: Unweaving the phenotypic rainbow

“…We argue that any re-conceptualization of the RTLA syndrome must await a fuller characterization of the mechanisms whereby RTLA wreaks its hedonic and homeostatic effects, with histopathological and molecular correlation ( 6 , 19 ). As the culprit pathologies are individually rare, this will entail collaboration between specialist centers, each implementing a uniform assessment protocol and collecting correlative neuroanatomical and neuropathological data.…”

“…As the culprit pathologies are individually rare, this will entail collaboration between specialist centers, each implementing a uniform assessment protocol and collecting correlative neuroanatomical and neuropathological data. However, cooperative enterprises of this kind will depend on a shared framework for defining the syndrome - as is amply endorsed by the work of Younes et al ( 4 ), Ulugut Erkoyun ( 5 ), and Campos et al ( 6 ). Any such framework should ideally be informed by a deeper understanding of how social and emotional concepts and reward value are represented in the healthy brain – and how these are modulated according to sensory experience, homeostatic state and behavioral goals.…”

“…In both syndromes, pathogenic protein spread targets a core, bi-temporally distributed semantic appraisal network ( 10 , 15 – 17 ). Furthermore, there is a strong, joint association with TAR-DNA-binding-protein (TDP)-43 type C as the underlying proteinopathy ( 3 , 6 , 11 ), albeit with greater genetic and histopathological heterogeneity in RTLA ( 18 , 19 ).…”

“…Three canonical clinico-anatomical syndromes of FTD are currently recognized: non-fluent variant primary progressive aphasia (nfvPPA), characterized by impaired language output, with predominant anterior left peri-Sylvian atrophy; semantic variant primary progressive aphasia (svPPA), characterized by impaired understanding of words, objects, concepts and socio-emotional signals, with predominantly left-sided antero-mesial temporal lobe atrophy; and behavioral variant frontotemporal dementia (bvFTD), characterized by impaired behavioral regulation and disordered inter-personal conduct and awareness, with a variable atrophy profile. The syndromes of bvFTD and svPPA have an important interface of clinical and neuroanatomical overlap, with a key locus in the right anterior temporal lobe: patients with selective or disproportionate right temporal lobe atrophy (RTLA) may have a distinctive clinical syndrome spanning the bvFTD-svPPA interface, however encapsulating this syndrome has proved both challenging and controversial ( 4 – 6 ).…”