Objective      To compare the occurrence rate and distribution of spine sharp wave and high frequency oscillations inside and outside the irritative zone and seizure onset zone (SOZ) in secondary epilepsy patients by scalp electroencephalography (EEG) in order to evaluate the localization value for epileptogenic zone.       Methods      A retrospective analysis study of video electroencephalogram (V-EEG) data in our hospital from September 2011 to September 2012 including 37 patients with secondary epilepsy was carried out. The channels with interictal epileptiform discharges (IEDs) were defined as area A (namely irritability area) and those without IEDs were defined as area B. The channels with ictal discharge (ID) in 10 to 30 s before the seizure onset were defined as area C and those without ID were defined as area D. IEDs (1 to 30 Hz) and ripples (80 to 250 Hz) in each area were marked. We analyzed the occurrence rate

quantity

distribution and sensitivity

specificity and accuracy to determine the SOZ.        Results      (1) The total occurrence rate of IEDs and ripples was 100% (37/37) and 48.6% (18/37) in 37 patients

respectively

and that of IEDs was significantly higher (Chi-square test

P0.01). The average rates (times/min) of ripples in area A

B

C and D were 0.08±0.15

0.03±0.03

0.12±0.29

and 0.04±0.06

respectively

suggesting that the average rate of ripples of area A was greater than that of area B and area C greater than area D (t test

P0.01). (2) The average channel of ripples was 4.2±3.6 in each patient

significantly less than that of IEDs 12.4±5.8 (t test

P0.01). (3) Compared to the IEDs

the ripples were less sensitive (ripples 51.1% vs IEDs 81.6%) but more specific (ripples 87.9% vs IEDs 57.1%) and more accurate (ripples 80.6% vs IEDs 54%) in determining the SOZ.       Conclusion      High frequency oscillations are closely associated with epileptiform discharges in the epileptogenic zone of secondary epilepsy patients

with higher specificity to identify SOZ. But the sensitivity is too low to replace IEDs to identify SOZ independently. High frequency oscillations help IEDs to localize epileptogenic zone.