Abstracts

The offset of seizure activity is thought to be caused by increasing inhibition. Status epilepticus can be viewed as abnormal prolongation beyond the usual range and failure of inhibition. Thus, it is worth while to characterize the typical duration of seizures to arrive at a better definition of when the unusual - possibly status epilepticus - has begun.
We collected data prospectively from patients being evaluated with continuous video and scalp EEG. 10-20 electrode system and sphenoidal electrodes were used in a 32 channel acquisition system. We defined seizure duration as the time from earliest clinical or EEG change until the end of EEG. The following categories were used: simple partial seizure (SPS), complex partial seizure (CPS), secondarily generalized tonic-clonic seizure (SGTCS)) and primary generalized tonic-clonic seizures (PGTCS). The duration of SGTCS were subdivided in a CPS portion and tonic-clonic (TC) portion. We calculated median duration of each seizure type for each patient and these were winsorized excluding extreme upper and lower values. Then the mean duration across individuals for each seizure type was calculated. We compared the duration of different seizure types using the Mann-Whitney test and the duration of seizures of the same type occurring from sleep or wakefulness in the same patient using the Student t-test.
519 seizures were recorded in 179 patients. Of these, 72 were SPS, 368 CPS, 70 SGTCS and 9 PGTCS. The mean durations were as follows: SPS 37 sec (SD = 23 sec), CPS 95 sec (SD = 55 sec), SGTCS 178 sec (SD = 133 sec) and PGTCS 67 sec (SD = 4 sec). For SGTCS, the CPS portion was 97 sec (SD= 125 sec) and TC portion 73 sec (SD = 24 sec). Comparison between seizure types showed SGTCS [gt] CPS [gt] SPS (p[lt]0.0001). The duration of PGTCS were not significantly different from the TC part of SGTCS. Seizures with onset from wakefulness or sleep were no different in duration.
Although the duration of SPS and CPS is variable within and between patients, the durations in a large sample follows a normal distribution. Seizures lasting longer than 2.5 or 3 SD should raise concern of status epilepticus. For SPS, mean duration plus 2.5 was 95 sec (if 3 SD 106 sec); for CPS, mean duration plus 2.5 SD was 233 sec (if 3 SD 260 sec); for SGTCS mean duration plus 2.5 SD was 511 sec (if 3 SD 577 sec). Tonic-clonic seizure activity has a similar duration with primary and secondary onset. Duration is not affected by the patient[apos]s state at onset of seizure activity.