Semiologic differences between bilateral tonic-clonic seizures of focal onset and generalized onset

Focal semiologies have been described in idiopathic generalized epilepsies (IGE) and generalized-onset bilateral tonic-clonic seizures (GBTCS). These focal signs may lead to wrong diagnosis and inappropriate choice of antiseizure medications. We sought to investigate the differences in focal semiologic features between GBTCS and focal-onset bilateral tonic-clonic seizures (FBTCS).

We retrospectively reviewed video-EEG data of captured GBTCS and FBTCS over a period of five years. The presence or absence of 12 focal signs as well seizure duration and time to head version was tabulated for each seizure. We used the chi-square test for independence and Fisher's exact test to investigate the occurrence of each focal sign in FBTCS compared with GBTCS. Additionally, we used receiver operating characteristic (ROC) curves to explore if the seizure duration and time to head version from the ictal onset can reliably differentiate between FBTCS and GBTCS. Finally, we employed hierarchical cluster analysis to visualize how these focal signs appear in combination.

Head version (p <.001), preceding automatisms (p <.001), eye version (p <.001), unilateral facial clonic activity (p <.001), and mouth deviation (p =.004) were found to be significantly more frequent in FBTCS. Longer seizures were highly in favor of FBTCS whereas shorter time to head version from the ictal onset indicated GBTCS in the ROC curve analysis.

Though focal signs occur in GBTCS, careful evaluation of semiology can help the clinician distinguish FBTCS from GBTCS.