Objective To assess the impact of new clinical diagnostic criteria for frontotemporal dementia (FTD) syndromes, including primary progressive aphasias (PPA), on prior clinical diagnosis and to explore clinicopathological correlations.

Methods 178 consecutive neuropathologically ascertained cases initially diagnosed with a FTD syndrome were collected through specialist programmes: the Cambridge Brain Bank, UK, and Sydney Brain Bank, Australia. 135 cases were reclassified using the revised diagnostic criteria into behavioural variant (bvFTD), semantic variant PPA (sv-PPA), non-fluent/agrammatic variant PPA (nfv-PPA) and logopenic variant PPA (lv-PPA). Pathological diagnoses included FTLD-tau, FTLD-TDP, FTLD-FUS, FTLD-UPS, FLTD-ni and Alzheimer's disease (AD). Statistical analyses included χ² tests, analyses of variance and discriminant statistics.

Results Comparison of the original and revised diagnosis revealed no change in 90% of bvFTD and sv-PPA cases. By contrast, 51% of nfv-PPA cases were reclassified as lv-PPA, with apraxia of speech and sentence repetition assisting in differentiation. Previous patterns of pathology were confirmed, although more AD cases occurred in FTD syndromes (10% bvFTD, ∼15% sv-PPA and ∼30% nfv-PPA) than expected. AD was the dominant pathology (77%) of lv-PPA. Discriminant analyses revealed that object agnosia, phonological errors and neuropsychiatric features differentiated AD from FTLD.

Conclusions This study provides pathological validation that the new criteria assist with separating PPA cases with AD pathology into the new lv-PPA syndrome and found that a number of diagnostic clinical features (disinhibition, food preferences and naming) did not assist in discriminating the different FTD syndromes.