All patients have tonic seizures, which may be generalized tonic or focal tonic seizures. These often occur with high daily frequency. Tonic seizures typically consist of forward tonic flexion lasting seconds (e.g. 10 seconds) that may be singular or in a series, symmetric or asymmetric.
Erratic focal clonic seizures, including hemiclonic seizures may also occur (seen in one third of cases). Tonic-clonic (either generalized tonic-clonic or focal to bilateral tonic-clonic) seizures, epileptic spasms, myoclonic (either generalized myoclonic or focal myoclonic) seizures and alternating hemiclonic seizures can occur, but are uncommon.