Primary progressive aphasia: linguistic patterns and clinical variants.

We investigated whether primary progressive aphasias (PPA) reflect non-random degradation of linguistic dimensions that might be supported by different neural subsystems and to what extent this degradation contributes to the emergence of clinical entities: semantic (S), logopenic (L) and nonfluent (NF) aphasia; apraxia of speech was also considered if associated with language disorders (AOS/aph). Forty-two aphasic patients are reported. Two main definable patterns of linguistic deficits tended to emerge that corresponded with identifiable patterns of brain atrophy, and probably diseases: the S variant, which principally expresses the impact of a "deep" cognitive (semantic) disorder on language, and AOS/aph in which "peripheral" executive components play a significant role. By contrast, NF aphasia emerged as a heterogeneous variant due to disorganization of various dimensions within the linguistic domain, that assumes different patterns depending on the differential distribution of atrophy in the perisylvian regions.