Febrile seizure is one of the most common pediatric neurological conditions with a prevalence of 2-14% (1).The International League Against Epilepsy (ILAE) defined febrile convulsion as “a seizure occurring in childhood after one month of age, associated with a febrile illness not caused by an infection of the central nervous system, without previous neonatal seizures or a previous unprovoked seizure, and not meeting the criteria for other acute symptomatic seizures” (2). The risk factors for febrile convulsion are  male sex (3), sudden rise in temperature , infection of the upper respiratory system , positive family history (4), preterm birth and brain injury at birth , vitamin deficiencies (5), and changes in serum and cerebrospinal fluid trace element levels(1, 6, 7). On the other hand, high income families have a reduced risk of febrile seizure (8).
Based on the duration of the seizure, the presence of focal neurological symptoms and its recurrence in 24 hours, febrile seizures are divided into two types, simple and complex(5). Simple FS is benign and self -limited, and rarely causes status epilepticus (3). In the complex type, the seizure lasts longer than 15 minutes, or recurs in 24 hours, or there are focal neurological symptoms (9) . Complex febrile seizures can be seen in 22.6% of patients and their incidence of epilepsy will be up to 12%. (10). In dealing with a child who had febrile seizure for the first time, the question is always whether it is possible for the seizure to recur or not. Several risk factors are known to affect the recurrence of febrile seizures, including the patient's age, the degree of fever at the time of seizures, family history of epilepsy or seizures, type of simple or complex seizures (11). One method of determining the likelihood of seizure recurrence is electroencephalography.
 The EEG has been studied in many investigations in febrile seizure.  Some studies reported that in more than 90% of cases ,the EEG reports were normal (12) but it should be considered that pseudo-petit mal discharge (PPMD) pattern and abnormal EEG pattern are among the risk factors of febrile seizure. (13). A study concluded that the positive predictive value of epileptiform discharges was low in complex febrile seizure but it was twice higher in recurrent febrile seizures and concluded that epilepsy is unlikely in patients with normal EEG. (14)  Patients with abnormal discharge on electroencephalography are more likely to develop epilepsy.(10).On the other hand, in children with febrile seizure ,epileptiform  alterations are not uncommon (9) and therefore EEG is recommended especially for recurrent complex febrile seizure patients.(10) As mentioned above it is very important for the family to predict the chance of recurrence that may be possible with performing EEG. However, it may not be cost effective to do EEG for all febrile seizure patients. Therefore, we need to know for which patients the EEG should be performed. The aim of this study was to investigate the extent of abnormal EEG reports and its association with other risk factors of recurrence in febrile seizures in order to identify the appropriate cases to perform EEG.

 

Discussion

In this study, 170 patients admitted into Mousavi Hospital from April 2015 to March 2016 were evaluated. Thirty (17.6%) patients had an abnormal EEG report and normal EEG was seen in 82.4% of cases which is different from the study of Shukla  with 68% normal EEGs. (5) In the study of Joshi, 175 patients with complex febrile seizures, were evaluated and 39.43% showed abnormal ECG (15). In Maytal’s study, 33 children were diagnosed with complex febrile seizures, 8.6% of whom had abnormal electroencephalography (16).In a study in Kermanshah, Iran, 111 patients with complex febrile convulsions were studied during 2 years. The electroencephalogram was abnormal in 37.8% of patients, epileptic waves were seen in 9% and 28.8% had nonspecific abnormal waves (17). The prevalence of abnormal EEG in different studies ranged from 2-86%, which depends on the time of performing electroencephalography and the presence of risk factors in different patients (18).
In the present study, a significant relationship was found between abnormal EEG report and male gender. This result is consistent with Nishiyama ’s study which showed that male sex is an independent risk factor for febrile seizure (OR: 1.21 ) (3).According to Hemmati’s study, although abnormal EEGs were more common in girls (40%) compared to boys (34.15%), this difference was not statistically significant. These results are different from our results that showed abnormal reports were more significantly seen in males .This difference may be due to different studied populations (17).
In our study, there was a significant relationship between abnormal EEG findings and older age. In the study of Joshi, age over three years and neurological impairment on examination were significantly associated with abnormal EEG (15). A study conducted for two years on 107 patients with febrile seizures in Tehran showed that older age increases the likelihood of an abnormal EEG (19). These results are consistent with our study.
We found a significant relationship between abnormal EEG findings and positive family history of febrile seizures and epilepsy, previous history of febrile seizures in the patient, complex febrile seizure and longer duration of seizures. These findings are consistent with the study of Khodapanahandeh in Tehran (19).
In Hemmati’s study there was a significant relationship between abnormal EEG with family history of febrile seizures which is consistent with our study but unlike our study, he showed that family history of epilepsy was negative in individuals with abnormal EEG (17).
Our study showed abnormal EEG in17.6% of reports; The most common (66.6%) was nonspecific changes followed by 26.6% for spike & sharp electric discharges and 6.6 % for slow activity. The most common abnormal epileptiform discharges in Karimzadeh’s study were 27.6% slow waves in the early EEG and 36% sharp waves in late EEG (20). The presence of specific changes in electroencephalography such as focal and pseudo petit mal discharges are helpful in predicting epilepsy and recurrent febrile seizure (13, 21).
In a study on 82 children aged 6-60 months with first febrile seizure, EEG abnormality was observed in 7.3% of patients with complex febrile convulsion and the study concluded that complex febrile convulsion is an important risk factor for epilepsy (22).
In a retrospective study in Poland on   103 FS children aged 5–55 months, the EEG was performed between the 3rd – 7th days. Abnormal EEG was reported in 29% of patients and a weak correlation was found between the EEG abnormalities and duration of seizures. EEG abnormalities were recorded in 37% of patients with recurrent FS, and in 27% of non-recurrent individuals. This study showed that abnormal EEG is involved in all types of FS but only in Complex FS an EEG exam is routinely recommended. (23) . In this study in which EEG was performed at the same age and time of admission as our study, the frequency of abnormal EEG was higher than in our study, but similar to our results the abnormal EEG report was higher in complex febrile seizure.

 

Conclusion

Febrile seizure is a benign condition in childhood for which EEG should not routinely be carried out. Due to the higher risk of abnormal EEG reports in patients with complex febrile seizures, developmental disorder and family history of epilepsy and febrile seizure and age over 3 years, this study recommends performing an electroencephalogram for patients with these risk factors.

 

Acknowledgements

This study was part of a thesis for medical degree. We hereby appreciate all the participants in the study.

 

Conflicts of Interest

The authors declare that there is no conflict of interests.