Interictal regional paroxysmal fast activity on scalp EEG is common in patients with underlying gliosis.

OBJECTIVE

Interictal regional paroxysmal fast activity (RPFA) on scalp EEG is common in patients with focal cortical dysplasia (FCD). Little data exists regarding the presence of RPFA in other etiologies.

METHODS

We studied the association between RPFA and etiology on MRI in patients with drug resistant focal epilepsy undergoing presurgical evaluation in 2011. RPFA was defined as ≥3 consecutive spikes with a frequency of ≥10 Hz lasting ≥300 ms but <4 s.

RESULTS

626 patients fulfilled the inclusion criteria. Of these, 138 (22%) patients had RPFA while rest had other interictal epileptiform discharges (IEDs). RPFA was located at posterior head region in 52.2% patients, frontal regions in 24.6% patients and over temporal regions in 17.4% patients. Focal gliosis (61, 44%) and FCD (27, 19%) were common etiologies in patients with RPFA. Compared to patients with other IEDs, patients with RPFA were more likely to have focal gliosis (61/138 vs. 39/488; p < 0.0001) or FCD (27/138 vs 37/488; p < 0.001) as the etiology of epilepsy.

CONCLUSION

In developing countries, focal gliosis is more common than FCD as the underlying etiology in patients with RPFA on scalp EEG.

SIGNIFICANCE

Focal gliosis should be considered as one of the common substrate for RPFA on scalp EEG.