In clinical practice, epileptic seizures with focal onset and subsequent generalized motor involvement are referred to as secondarily generalized seizures.1,2 However, generalized motor manifestations do not necessarily imply that the entire or even bilateral cerebral cortex is producing the epileptic discharges.3 Focal seizures arising from the supplementary motor cortex or basal ganglia also can produce clinical signs of generalized motor activity.4 Conversely, bilateral and widely spread ictal electroencephalographic (EEG) patterns can be found in patients with minimal or subtle motor activity during a secondarily generalized seizure (Case 11-1).5 Thus, the operational definition of secondary generalization in the era of video-EEG monitoring (VEM) should be focal onset of an epileptic seizure with generalized or bilateral ictal electrographic propagation.6 According to the classification by the International League Against Epilepsy (ILAE), there are three different types of secondarily generalized seizures: tonic-clonic seizures, absence seizures, and epileptic spasms (Table 11-1).1,7,8 Differences in clinical presentation and EEG findings of these seizure types are compared in Table 11-2. Although partial onset seizures do not commonly progress to secondarily generalized seizures, more than 60% of patients with partial seizures may experience tonic-clonic seizures.9 Not all secondarily generalized convulsions progress from complex partial seizures, and up to 20 to25% of them are directly evolved from simple partial seizures, which suggests multiple cortical and subcortical routes of spread are possible for secondary generalization.10
At age 49, as the patient's family noted, the patient tended to “fall into [sic] sleep easily,” with extreme difficulty of arousal. Her brain magnetic resonance imaging (MRI) and EEG were normal, and the diagnosis of epilepsy was eventually made about 8 years later. The beginning of Video 11-1 corresponds to the arrow in Figure 11-1, which already shows diffuse ictal rhythmic theta changes bilaterally. Even though the patient's ictal EEG showed a secondarily generalized pattern, she had little or subtle motion, without the appearance of tonic or clonic activity.
Electroencephalographic (EEG) onset of Case 11-1. Ictal EEG changes 20 seconds after the initial EEG onset in Case 11-1. Ictal EEG changes 35 seconds after the EEG onset and start of the clinical seizure in Case 11-1. EEG shows bilateral diffuse rhythmic 4 to 5 Hz discharges. Ictal EEG changes 55 seconds after the EEG onset in Case 11-1, showing diffuse bilateral changes.
Table 11-1Classification of Secondarily Generalized Seizures |Favorite Table|Download (.pdf) Table 11-1 Classification of Secondarily Generalized Seizures
|Type of Seizure ||Description |
|Tonic-clonic seizures ||Probably consist of multiple types and may involve different pathophysiologic mechanisms and anatomical substrates, at least initially, than generalized tonic-clonic seizures with generalized onset |
|Absence seizures ||Rarely represent propagation from localized cortical areas, usually in ...|