Purpose: Secondarily generalized seizures (SGSs) are often considered to be stereotyped, presumably sharing a common electrical pathway. We examined whether SGSs are uniform in a homogeneous group of patients with mesial temporal epilepsy, and whether certain clinical signs associated with generalization are lateralizing with regard to seizure origin.
Methods: A comprehensive, standardized video/EEG analysis was performed of the clinical characteristics of 29 patients (69 SGSs) with mesial temporal seizure onset.
Results: The sequence of tonic postures, as well as the sequence of tonic and clonic activity, was variable in SGSs of mesial temporal origin. The sequence of tonic activity, followed by vibratory and then clonic activity alone, was seen only in 51.7% of patients. Tonic and clonic activity could occur simultaneously. The most common clinical signs were forced head deviation (89.7%) and vocalization (75.9%). The most common tonic posture was bilateral arm extension (72.4%). All other clinical signs occurred in <60% of patients. Among these, early forced head deviation, asymmetric tonic facial contraction, tonic arm abduction with elbow flexion, and tonic arm extension combined with opposite arm flexion had lateralizing significance. The preceding partial seizure in SGSs (mean, 43.6 s) was significantly shorter than partial seizures without generalization (mean, 105.2 s; p < 0.001). SGSs occurred more often out of sleep (p < 0.01).
Conclusion: Secondarily generalized seizures of mesial temporal origin are not uniform in their clinical presentation. The final phases of SGSs are more stereotyped than the initial clinical signs of generalization. This suggests variable electrical spread patterns, which may end in a common pathway. Some asymmetric motor signs have lateralizing significance. SGSs were associated with sleep and abbreviated partial seizures.