Asymmetric seizure termination in primary and secondary generalized tonic-clonic seizures

In temporal lobe epilepsies an asymmetric termination (AST) of the clonic phase of secondary generalized tonic-clonic seizures (sGTCS) reliably lateralizes the side of seizure onset. The last clonic activity occurs ipsilateral to the side of the seizure onset zone. We compared the prevalence and lateralizing value of AST in sGTCS of frontal and temporal lobe origin as well as in primary generalized tonic-clonic seizures (pGTCS).

We analyzed 177 seizures in 84 consecutive patients. Forty-one patients had temporal lobe epilepsy (TLE), 24 frontal lobe epilepsy (FLE), and 19 had nonfocal (primary) generalized epilepsies (GE). All patients underwent intensive video-EEG (electroencephalography) monitoring, high-resolution magnetic resonance imaging (MRI), neuropsychological testing, and single photon emission computed tomography/positron emission tomography (SPECT/PET) when feasible. Two investigators blinded for diagnosis, EEG, and imaging data assessed frequency and side of the last clonic jerk.

AST occurred in 63% of patients with TLE (47% of seizures), in 71% with FLE (60% of seizures), and in 42% with GE (21% of seizures). These results were not significant for patients, but significant for seizures in TLE versus GE and in FLE versus GE (p < 0.001). The positive predictive value (PPV) for the side of seizure onset was 74% (p = 0.003) in TLE and 75% (p = 0.008) in FLE.

AST in sGTCS lateralizes the side of seizure onset in TLE and in FLE to the ipsilateral hemisphere with a high PPV. However, AST was also observed in GE. Therefore, asymmetric clinical signs should not inevitably lead to the assumption of focal epilepsy syndromes.