PPA is a term that has been used to encompass all patients with progressive language impairment as the initial feature of a degenerative disorder (Mesulam, 1982; Mesulam, 2001; Mesulam, 2003). ere is overlap with the frontotemporal dementia (FTD) spectrum both pathologically and genetically (Neary et al., 1998; Mackenzie and Rademakers, 2007). Although some research groups have previously classied all language disorders under this one term of PPA (Mesulam 2001; Mesulam et al., 2003), it is clear that a number of subtypes can be identied (see reviews by Grossman et al., 2004; Amici et al., 2006; Hodges and Patterson, 2007; Mesulam et al., 2007; Rohrer et al., 2008a; Grossman, 2012; Mesulam et al., 2014). e uency of speech output forms the basis for a basic clinical descriptive subclassication of PPA; however, uency is oen problematic to operationalize; it has been used to refer to reduced, eortful or sparse speech, however these may map onto distinct syndromes within the PPA syndrome. Semantic dementia (SD) or semantic variant PPA (svPPA) is a homogeneous
clinico-pathological entity with characteristic clinical, neuropsychological and radiological ndings (see Chapter 68). SvPPA presents usually with a ‘uent’ aphasia (and therefore has previously been called uent PPA: Adlam et al., 2006), however two other major PPA syndromes are associated with ‘nonuent’ language output: these nonuent disorders, progressive nonuent aphasia (PNFA) or nonuent variant PPA (nfvPPA) and logopenic aphasia (LPA) or logopenic variant PPA (lvPPA), are discussed in detail in this chapter. It remains unclear if these are the only subtypes of PPA and how this heterogeneous group of conditions maps onto the underlying genetic and pathological causes. While early nfvPPA can resemble Broca’s aphasia and early lvPPA may resemble conduction aphasia (Hachisuka et al., 1999; reviewed in Rohrer et al., 2008a), the PPA subtypes do not correspond closely with the acute aphasia syndromes of stroke, due both to diering neuroanatomical patterns of involvement and the progressive nature of the disease. Initial consensus criteria for PNFA and SD (Neary et al., 1998) and other criteria for PPA as a unitary syndrome (Mesulam, 2001, 2003) have recently been updated, dening criteria for the semantic, nonuent and logopenic variants of PPA (Gorno-Tempini et al., 2011).