Warrington reported three cases with associative agnosia and a fluent-type aphasia characterized by anomia and impaired word comprehension attributed to circumscribed asymmetric atrophy in the anterior temporal lobe, which was considered a selective impairment of semantic memory. Also, this feature was described by Snowden et al. as semantic dementia (SD) [23]. Later, Hodges et al. provided a comprehensive characterization of SD [24]. In 1998, Neary et al. developed diagnosis criteria for SD in relation to frontotemporal lobar degeneration (FTLD) [1].

The diagnosis of SD required a gradually progressive language disorder characterized by fluent, empty, spontaneous speech, loss of word meaning manifested by impaired naming and comprehension, preserved single-word repetition, and preserved ability to read aloud and write down orthographically regular words that are dictated [25]. Instead of the language disorder, individuals with prosopagnosia (impaired recognition of identity of familiar faces) and/or associative agnosia (impaired recognition of object identity) could also be diagnosed as having SD. Other aspects of cognition could be intact or relatively well preserved. Behavioral and personality changes characterized by loss of sympathy and empathy, narrowed preoccupations, and parsimony are included in the supportive diagnostic features, as these changes are considered characteristic of SD and often associated with high diagnostic specificity.

The neuroimaging shows atrophy and hypometabolism and/or hypoperfusion in the middle, inferior, and anterior temporal lobes bilaterally but asymmetrical, with the left side usually being more affected [14] (Fig. 13.2a–c).

Grossmann et al. reported a different form of progressive language disorder, which was marked by dysfluent and effortful speech, hesitations, and errors in the production of speech sounds, and termed it progressive nonfluent aphasia (PNFA) [26]. In 1998, Neary et al. developed diagnostic criteria for PNFA in relation to FTLD [1].

The diagnosis of PNFA required gradually progressive nonfluent spontaneous speech with at least one of the following symptoms: agrammatism, phonemic paraphasias, or anomia [25]. Other aspects of cognition could be intact or relatively well preserved. Late behavioral changes similar to bvFTD are included as supportive diagnostic features.

The neuroimages show predominantly atrophy and hypometabolism and/or hypoperfusion in the left posterior frontal–insular region [27–29] (Fig. 13.3a–c).