A Data‐Driven Operational Definition of Square‐Wave Jerks and Its Diagnostic Utility in Progressive Supranuclear Palsy
Duy Duan Nguyen, Andrea Quattrone, Mark Paine, Amir Fazlollahi, Soohyun Lee, Baibin (Ben) Wang, Tanya Davidson, Felicia Coleman, John D. O'Sullivan, Peter J. NestorABSTRACT
Background
The Movement Disorder Society diagnostic criteria for progressive supranuclear palsy (PSP) list frequent square‐wave jerks (SWJ) as a suggestive oculomotor feature. A standardised operational definition of SWJ is however presently lacking.
Objective
To create a data‐driven optimal SWJ definition and to assess its diagnostic utility in PSP.
Methods
We prospectively recruited PSP n = 25, Parkinson's disease (PD) n = 32, Alzheimer's disease (AD) n = 35, and controls n = 88. SWJ were recorded with a visual fixation task using video‐oculography. Multiple candidate definitions of SWJ were generated by systematically varying morphological features, producing 32 candidate definitions. A nested cross‐validation was used to obtain unbiased diagnostic performance and optimised SWJ definition. Results were then externally tested in a fully independent sample of n = 25 PSP, n = 41 PD and n = 25 controls.
Results
The optimal selected SWJ definition consisted of saccade amplitude 1°–8°, intra‐SWJ intervals 20–600 ms, directional opposition within ±45°, and amplitude similarity ≤ 0.25. Only SWJ rate, and not morphological features, was distinctive for PSP. SWJ rate gave out‐of‐fold AUCs of 0.81 for PSP versus controls, 0.71 for PSP versus AD, 0.63 for PSP versus PD, and 0.76 for PSP versus all non‐PSP groups. Post hoc analyses using this data‐driven definition on the external validation cohort yielded relatively comparable results. SWJ rate > 24/min had high specificity, but low sensitivity, for PSP when compared with PD.
Conclusions
SWJ rate was significantly increased in PSP but with insufficient discriminant ability for use as a stand‐alone diagnostic marker. This data‐driven definition may serve as a reproducible operational definition for future research.