Validation of the Telephone MoCA in iRBD and Parkinson's Disease with Conversion to the Standard MoCA

BACKGROUND: Telephone-based cognitive assessment may improve follow-up when face-to-face testing is impractical. The Telephone Montreal Cognitive Assessment (T-MoCA) omits visually dependent items from the standard MoCA, but its validity in isolated REM sleep behavior disorder (iRBD) and Parkinson's disease (PD), remains uncertain. OBJECTIVES: To assess agreement between the T-MoCA and face-to-face MoCA-22 in iRBD and PD, and derive and externally validate a MoCA-22 to MoCA-30 conversion. METHODS: In the Oxford Parkinson's Disease Centre (OPDC) Discovery Cohort, 137 participants (38 controls, 47 iRBD, 52 PD) completed T-MoCA and MoCA-22 assessments. Agreement was evaluated using Lin's concordance correlation coefficient, Bland-Altman analysis, and equivalence testing with ±1-point bounds. Equipercentile equating with log-linear smoothing was used to derive a MoCA-22 to MoCA-30 conversion using Discovery data (3561 tests), with validation in Tracking Parkinson's (5767 tests) and Parkinson's Progression Markers Initiative (5047 tests). RESULTS: T-MoCA and face-to-face MoCA-22 scores were statistically equivalent, with minimal bias; 83.3% of scores differed by ≤1 point. However, concordance between test formats was moderate (Lin's CCC = 0.58). Across 14,375 MoCA assessments, equipercentile equating outperformed proportional scaling in development and validation cohorts. Propagating T-MoCA-MoCA-22 variability resulted in wider prediction intervals for T-MoCA-derived MoCA-30 estimates, indicating individual-level uncertainty, with intervals estimable only for T-MoCA scores ≥17 due to sparse data. CONCLUSIONS: At group level, T-MoCA is a valid remote measure of non-visual MoCA domains in iRBD and PD. The equating function supports cohort-level harmonization of MoCA-22 and MoCA-30 scores, while individual T-MoCA-derived MoCA-30 estimates should be interpreted with caution.