Quantitative analysis of clonic upper limb movements in bilateral Tonic-Clonic seizures and Functional/Dissociative...

Bilateral tonic-clonic seizures (BTCS) and functional/dissociative seizures (FDS) can present with similar motor manifestations, complicating differential diagnosis based on visual examination alone. This retrospective study applied optical flow analysis of video electroencephalography (VEEG) recordings from BTCS and FDS patients to quantitatively compare upper limb rhythmic clonic movements for possible differentiation.

Optical flow was calculated within a region of interest covering one upper limb using the Farnebäck method, and principal component analysis was applied to extract a one-dimensional motion waveform (principal component 1, PC1) for each event. Primary outcome measures were (1) temporal change in PC1 interpeak interval as assessed by Kendall's τ, (2) logarithmic regression line slope of PC1 amplitude with time (amplitude decay slope, ADS), and (3) integrated absolute PC1 amplitude (|PC1|). Metrics were compared between patient groups by Mann-Whitney U test.

The VEEG records of 27 BTCS and 15 FDS patients were analyzed. Kendall's τ was significantly higher in the BTCS group, indicating progressively longer clonic intervals over time (p < 0.001), while ADS was more negative in BTCS, reflecting greater attenuation of movement amplitude (p < 0.05). Integrated |PC1| was also significantly higher in the BTCS group (p < 0.001). Scatter plots of these primary metrics suggested multivariate separation between BTCS and FDS.

Optical flow analysis enabled quantitative extraction of upper limb clonic movement temporal structure and amplitude from VEEG. These quantitative metrics of seizure-related motor activity may provide complementary support in the differential diagnosis of BTCS and FDS.