Table 1.

Summary of anatomic, cognitive, and emotional/behavioral alterations observed in the FTD variants.

FTD variant	Anatomical alterations	Cognitive and behavioral alterations
Behavioral FTD	Atrophy in the frontal and temporal lobes, the insula and the anterior cingulate cortex (ACC), with the earliest involvement of frontal paralimbic cortices and insula (Meeter et al., 2017).	Remarkable change in personality with prominent apathy and disinhibition, accompanied by a lack of empathy and insight, stereotypical behaviors and changes in eating habits, obsessive-compulsive behaviors. Executive dysfunctions and altered social cognition are also observed yet with relative preservation of other cognitive areas such as visuospatial function and memory in the early stages (Musa et al., 2020).
Semantic variant of primary progressive aphasia	Asymmetrical (commonly left- sided) antero-inferior temporal lobe atrophy, hypometabolism or hypoperfusion	Anomia, impaired object knowledge, particularly for low- frequency or low-familiarity items, progressive loss of word meaning and impaired single words comprehension but with preserved fluency and repetition. Possible surface dyslexia and dysgraphia (Gorno-Tempini et al., 2011).
Non-fluent/agrammatic primary progressive aphasia	Predominantly left-sided inferior fronto-insular atrophy, hypometabolism or hypoperfusion	Characterized by agrammatism and/or apraxia of speech with progressive uncertainties of speech that in turn progress to mutism. Impaired comprehension of syntactically complex sentences, but with spared object knowledge and word comprehension (Gorno-Tempini et al., 2011).
Logopenic primary progressive aphasia	Left temporoparietal junction, posterior perisylvian or parietal atrophy, hypometabolism or hypoperfusion	Impaired single-word retrieval in spontaneous speech and naming and impaired repetition of sentences and phrases, possible phonological errors in spontaneous speech and naming but with spared single-word comprehension and object knowledge, motor speech and absence of frank agrammatism (Gorno-Tempini et al., 2011).