Semiology of spontaneous generalized tonic-clonic seizures in the epileptic baboon

The epileptic baboon provides an animal model for juvenile myoclonic epilepsy (JME), demonstrating spontaneous generalized tonic-clonic seizures (GTCS) in addition to generalized myoclonic, absence and multifocal seizures. While photoconvulsive responses have been described in this model, spontaneous GTCS have not been characterized.

In this study, we characterized 46 seizures in 7 epileptic baboons (5 females, 12 ± 3 years old) by video recording. While housed in single cages, the baboons were monitored for a median of 2 (range 1-10) weeks, with high-resolution, infrared-capable camera systems. Each GTCS was evaluated for evidence of preconvulsive ictal symptoms, focal convulsive behaviors, duration of the preconvulsive and convulsive periods, postictal immobility, and recovery of an upright posture. The circadian pattern of GTCS was also for each baboon.

More than half of GTCS occurred in sleep, beginning from an upright position in all but one tethered baboon. Focal semiological findings were noted in 19 (41%) GTCS, and these included preconvulsive focal ictal motor behaviors as well as lateralized motor activity during the convulsions. The convulsive portion lasted 47 ± 10 seconds, whereas the entire seizure lasted 54 ± 21 seconds. Postictally, the baboons remained immobile for a median latency of 40 (range 14-347) seconds, recovering an upright posture after 173 (range 71-1980) seconds. GTCS demonstrated circadian patterns in all but one baboon, with 34 (74%) all seizures occurring between 1-9 am.

GTCS in the baboon revealed intersubject variability, but semiology remained stereotyped in a given baboon. Similar to GTCS in people with JME, focal symptoms were also observed in epileptic baboons. The postictal recovery period, characterized by postictal immobility and myoclonus as well as time to recumbency, also varied among baboons.