A brief assessment of object semantics in primary progressive aphasia

Background: A cross-culturally valid nonverbal assessment of semantic knowledge is needed. Accurately identifying impairment of object semantics is important for diagnosis of several disorders, including distinguishing semantic variant primary progressive aphasia (svPPA), a neurodegenerative condition characterised by progressive impairment in word comprehension, from logopenic and nonfluent agrammatic variants, which are not associated with impaired object semantics. However, current assessments require culturally specific knowledge.

Aims: We developed a cross-culturally valid short form of the Pyramids and Palm Trees Test to assess object semantic memory. We investigated its clinical utility in differentiating the semantic variant of primary progressive aphasia, from the logopenic and nonfluent agrammatic variants. Areas of atrophy associated with poor performance were identified.

Methods & Procedures: Fourteen items that rely on knowledge of objects’ defining features were selected from the original 52-item version. The full and short forms were administered to healthy individuals in the US (N = 18), Argentina (N = 20), and Greece (N = 12) and performance was compared. Seventy-eight individuals with primary progressive aphasia in the US completed the short form. Behavioural performance of the svPPA group (N = 24) was compared to other variants. Atlas-based analysis identified regions where atrophy correlated with poor performance in 39 individuals with primary progressive aphasia who had high-resolution magnetic resonance imaging (MRI) scans.

Outcomes & Results: Control performance was classified as normal on the short form significantly more often than on the full version. Across groups with primary progressive aphasia, the group with semantic variant performed significantly worse than the groups with logopenic or nonfluent agrammatic variants. Volume in left anterior and inferior temporal cortex correlated with performance.

Conclusions: The short-form Pyramids and Palm Trees Test is a clinically relevant, cross-culturally valid assessment of nonverbal object semantics. It can be used to identify semantic impairments, with poor performance associated with atrophy of the temporal lobes.