To evaluate the interrater reliability of the Parkinsonism Atypical Features Assessment (PAFA), a novel clinical outcome assessment, in a retrospective cohort.

The PAFA is a 36-question (8-domain) rater-based scale developed using established diagnostic criteria for Parkinson’s disease (PD) and atypical parkinsonian syndromes. While designed primarily as a prospective assessment, we piloted the PAFA using a retrospective chart review of postmortem cases. Three independent movement disorders specialists completed the PAFA, indicating “Yes” for each atypical feature that was present and could not be attributed to confounding factors. The frequency of endorsement of each feature was assessed, and interrater reliability coefficients were calculated for those with endorsement rates ≥10%.

Twenty-six cases (all male; ages 68-91; 24 White, 2 Black) were included. Neuropathological diagnoses included 17 PD/Lewy body disease; 3 PD; 2 progressive supranuclear palsy (PSP); 1 PSP/PD co-pathology; 1 PSP/amygdala Lewy body co-pathology; 1 PSP/CBD co-pathology; and 1 frontotemporal lobar degeneration-TDP-43. Thirteen questions had <10% endorsements due to rarity or absence of the feature in the cohort, insufficient data, or clinical confounders. Of the 23 questions with ≥10% endorsements, 17 had Fleiss’ kappa values consistent with moderate (0.41-0.60, n=9) or substantial-to-near perfect (0.61-0.81, n=8) interrater reliability.