Chapter 8: Generalized Epilepsy

Carbamazepine-Induced Myoclonic Seizure. A 3-year-old boy with a history of GTCS who developed frequent myoclonic jerks and drop attacks 2 weeks after starting the treatment with carbamazepine (CBZ). Ictal EEG during one of his myoclonic seizures shows a burst of generalized polyspike-and-slow-wave discharge followed by a brief diffuse electrodecrement and 5-Hz theta slowing. Myoclonic seizures and drop attacks disappeared 2 days after stopping CBZ.

CBZ is the most common antiepileptic drug (AED) causing AED-induced seizure worsening. CBZ can both aggravate and induce new seizure types including absence, atonic, or myoclonic seizures in patients with generalized epilepsies. Vigabatrin and gabapentin have been found to induce absence and myoclonic seizures. Benzodiazepines have been reported to precipitate tonic seizures in patients with Lennox–Gastaut syndrome. Lamotrigine has been reported to worsen myoclonic, clonic, and tonic-clonic seizures in the patients with Dravet syndrome.^1–3 Therefore, “AED-induced seizure worsening” must be considered in all patients whose seizures are worse with the introduction of the new AED.

Generalized Tonic-Clonic Seizure (GTCS). A 14-year-old girl with a history of idiopathic generalized epilepsy (IGE). EEG shows recruiting rhythm described as rhythmic generalized alpha and theta frequency activity. Approximately 22 sec into the seizure, the background activity becomes obscured by myogenic artifact (arrow head) during generalized tonic stiffening.

Generalized Tonic-Clonic Seizure (GTCS). (Continued) The fast spike activity characterizes the tonic phase of GTCS. However, the background EEG activity becomes almost completely obscured by myogenic artifact during the tonic posturing. Digital high-frequency filter of myogenic artifact or EEG performed during paralyzing with muscle relaxant allows visualization of the EEG activity.

Generalized Tonic-Clonic Seizure (GTCS). (Continued) During the clonic phase of GTCS, the fast spike activity becomes discontinuous and is replaced by high-voltage generalized polyspike-wave activity with polyspikes corresponding with clonic jerks and brief relaxation with slow waves. Immediately after the seizure stops, markedly generalized background suppression is noted. Very irregular diffuse slow-wave activity then follows and may last for minutes. In patients with secondarily GTCS, asymmetric postictal slowing can be a very important lateralizing sign.

Tonic Phase of Generalized Tonic-Clonic Seizure; (Subdural EEG Recording). Subdural EEG allows visualization of the EEG activity during tonic phase of generalized tonic-clonic seizure without myogenic artifact. EEG shows 4-Hz spike-wave activity during tonic posturing. Tonic and clonic phase of GTCS share similar EEG finding of spike-wave activity but with different duration of relaxation (slow wave). Note myogenic artifact in the EKG channel that represents muscle contraction during the tonic phase of GTCS (lowest channel).