Introduction

Primary progressive aphasia (PPA) is an umbrella term which identifies a group of neurodegenerative diseases manifested by relatively isolated language disorders. The logopenic variant (LPA), is characterised by a ‘word-on-the-tip-of-the-tongue phenomenon’ and anomia as well as by comprehension and repetition difficulties for sentences due to verbal working memory deficits.1 Cortical atrophy typically affects the left temporal-parietal junction.1 According to most studies LPA is primarily due to underlying Alzheimer's Disease (AD) pathology as suggested by biomarker findings from positron emission tomography with Pittsburgh compound B binding to amyloid deposits (PET-PIB) imaging and CSF (cerebrospinal fluid) β-amyloid and τ measures as well as by neuropathological data.2

However, PET-PIB and CSF data are drawn from relatively small PPA populations, which makes it difficult to conclude that LPA is invariably underpinned by AD pathology. Furthermore, neuropathological results from the most important sample of LPA patients have demonstrated that only seven out of 11 patients had AD while the remaining four patients had pathology characteristic of frontotemporal lobar degeneration.2 Finally, follow-up studies showing that LPA …