2026 American Academy of Neurology Abstract Website

Objective:

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

Background:

Degenerative parkinsonian syndromes present diagnostic challenges due to overlapping clinical features, progression of symptoms over time, and frequent co-pathology reflecting involvement of more than one neurodegenerative pathway. While existing scales characterize and monitor progression of individual parkinsonian syndromes, there remains a critical need for a brief, comprehensive assessment to evaluate the broad range of atypical features occurring in these disorders.

Design/Methods:

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%.

Results:

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.

Conclusions:

When used retrospectively, the PAFA demonstrated moderate-to-near perfect interrater reliability for almost 75% of the atypical features identified in the cohort. These findings will facilitate refinement of the PAFA for future prospective validation studies in larger, more diverse populations.