First-time seizures may take the form of isolated seizures, repeated seizures or status epilepticus. Repeated seizures within one day are considered a single seizure episode.1 Electroencephalography is a noninvasive, readily available, and inexpensive investigative tool in diagnosis, identification of specific syndromes, and long-term prognosis. It also helps differentiate seizures and predict the risk of recurrence.8
In this study, there were 54 abnormal EEG examinations from 100 children with FUS, and 68% of the abnormal examinations showed epileptiform discharge. The rate of abnormal EEG ranged from 41–80% in non-selected populations and from 9–63% in selected populations.6 Schreiner and Pohlmann-Eden stated that there only 10% of their patients with FUS had normal EEG results.9 Epileptiform activity was reported in 12–27% of routine EEG recordings, increasing to a range of 23–50% if the sleep phase could be recorded.6 Yusaku Miyamoto et al. found abnormal EEG results in 61% of children with FUS.10 This was similar to the results of the present study, which found that more than 50% of children in the sample had EEG abnormalities. However, Bhat et al. reported that EEG abnormalities were detected in only 32.3% of children. The difference in EEG abnormality rates between that study and the present one might be due to time variations and EEG recording methods.9
In addition, the present study found a relationship between age and abnormal EEG results (p = 0.007), where children ≥ 5 years old had a higher prevalence of abnormal EEG waves (50%) than younger children. A study reported by Sakir Delil et al. described abnormal EEG results in older patients.10 Takayuki Tsuboi also noted that the amount of visible abnormal "spike-wave" EEG activity increased with age.11 The difference in EEG features by age was probably due to the first seizure onset and the migration of the EEG focus during the clinical course.12
Seizures are produced by abnormal excessive electrical activity in neurons. A focal seizure is a type of seizure that begins in one part of the brain. Focal seizures can be caused by irritation, infection, or injury in the brain. Many children with focal seizures are eventually diagnosed with epilepsy.13,14 The present study found an association between seizure type and abnormal EEG waves (p = 0.03), with abnormal EEG waves being more common in focal than generalized seizures. A study undertaken by Khair et al., which examined the EEG results from children who suffered first-time seizure without fever, stated that children with focal seizures had a higher prevalence of abnormal EEG waves than children with generalized seizures (47.5% > 44.44%); however, this difference was not statistically significant. Despite the nonsignificance of this result, doctors still tended to obtain abnormal EEGs more easily following a focal first seizure than a generalized first seizure, perhaps in the process of trying to localize the epileptic focus.14
Prolonged seizures (lasting 5 minutes or longer) have a remarkably unfavourable long-term prognosis, with a high risk of events such as neurological death, nerve injury, and changes in neural tissue, especially if the seizure duration is longer than 30 minutes.15 The American Academy of Pediatrics advised parents whose children had seizures to contact emergency medical services if the seizure lasted more than 5 minutes and there was no rescue medication available at home or if the seizure lasted more than 5 minutes after the rescue medication was given.16 Our findings confirmed that seizure duration is an essential factor related to abnormal EEG results (p < 0.001), with an increased prevalence of abnormal EEG in patients whose seizures lasted ≥ 5 minutes. Several previous studies also reported that extended seizure duration was associated with intracranial abnormalities and generally increased the risk of recurrent seizures.17–19
Strengths and limitations
The main limitation of the present study was that it used conventional EEG and not 24-hour EEG; thus, limited inferences can be made from the available recordings. The strength in this study is that brief EEG recording for maximum 48 hours after FUS can depicts the abnormality clearer and more visible. The evidence from our study expands the knowledge on the abnormality of EEG after FUS, especially in resource limited country settings.