Right Anterior Temporal Degeneration, Emotions, and Loss of Nonverbal Semantics: The Emotional Semantic Variant Frontotemporal Dementia
Authors: Younes Kyan , Borghesani Valentina , Montembeault Maxime , Spina Salvatore , Mandelli Maria Luisa , Welch Ariane E. , Weis Elizabeth , Callahan Patrick , Elahi Fanny M. , Hua Alice Y. , Perry David C. , Karydas Anna , Geschwind Daniel , Huang Eric , Grinberg Lea T. , Kramer Joel H. , Boxer Adam L. , Rabinovici Gil D. , Rosen Howard J. , Seeley William W. , Miller Zachary A. , Miller Bruce L. , Sturm Virginia E. , Rankin Katherine P. , Gorno-Tempini Maria Luisa 
Published: June 2021

It has been proposed that focal anterior temporal lobe (ATL) degeneration is a specific, unitary FTLD-TDP-related disease that initially preferentially affects the left or right hemisphere. Patients with early left ATL (lATL) atrophy show severe anomia and verbal semantic deficits and meet criteria for semantic variant primary progressive aphasia (svPPA) and semantic dementia, prompting appropriate neurological care. There is less consensus regarding the symptoms in right ATL (rATL) predominant cases, who most often present with behavioral and emotional changes leading to a misdiagnosis of a psychiatric disorder, and later of behavioral variant frontotemporal dementia (bvFTD). Uncertainties regarding early symptoms and lack of an overarching framework continues to hinder proper diagnosis and care of patients with rATL disease. Here, we present symptom chronology, cognitive and socioemotional profiles of a large, well-characterized, longitudinally followed cohort of patients with rATL-predominant degeneration and propose new criteria and nosology for the syndrome.

We identified individuals with a clinical diagnosis of bvFTD or svPPA and a structural MRI (n=478). Based on neuroimaging criteria, we identified three groups: patients with rATL-predominant atrophy with relative sparing of the frontal lobes (n=46), patients with frontal-predominant atrophy with relative sparing of the rATL (n=79), and patients with lATL-predominant atrophy with relative sparing of the frontal lobes (n=75). Seventy-eight patients had undergone autopsy. We analyzed patients’ clinical, neuropsychological, genetic, anatomical, and pathological profiles.

In the rATL-predominant group, the earliest symptoms were loss of empathy (27%), person-specific semantic impairment (23%), and complex compulsions and rigid thought process (18%). On testing, this group exhibited greater impairments in emotional theory of mind, identifying famous people from names and face, and facial affect naming (despite preserved face perception) than the lATL- and frontal-predominant groups. The clinical features were highly sensitive (81%) and specific (84%) in differentiating rATL from bvFTD in the first three years of the disease. FTLD-TDP (84%) was the most common pathology.

Our results suggest that rATL-predominant degeneration is characterized by early loss of empathy and person-specific knowledge, deficits that are caused by progressive loss of semantic memory for concepts of social-emotional relevance. Although this syndrome exists along a clinical, anatomical, and pathological continuum with svPPA, patients present with progressive behavioral changes. To facilitate early identification and care in clinical and research settings, we propose specific diagnostic criteria and the term “emotional semantic variant frontotemporal dementia” to distinguish this syndrome from other forms of frontotemporal dementia.