A study on EEG findings : An Experience from a Tertiary Care Center of Nepal

Introduction: The electroencephalography (EEG) is the recording of brain’s spontaneous electrical activity over a period of time (15-20) minutes recorded from multiple electrodes placed on the scalp. It is used in seizure disorder, organicity, and psychiatric conditions. There is a paucity of literature with regard to the application of EEG in various conditions in our setting. Objective: The current study aims to explore the EEG findings of different cases and their associations in various clinical scenarios. Method: It is a retrospective study on the patients who underwent EEG in the EEG room of Department of Psychiatry at Patan Academy of Health Sciences (PAHS), Nepal for a year. Information was obtained from EEG register and reports. Data were analyzed using IBM SPSS version 23. Frequency distribution was studied and Chi Square test was applied for categorical variables. The only continuous variable studied was the age for which mean, median and standard deviation were computed and the suitable statistical tool was applied after normality testing. Result: Of the total 164 patients studied, mean age was 21.93 years and 51.2% were male. The common reason for EEG referral was to rule out seizure disorder (80.5%), requested mostly from the department of Psychiatry. EEG abnormality was seen in 43.3% with EEG diagnosis of generalized epilepsy in 26.21% and slow wave (46.2%) as the most common EEG finding. Abnormal EEG detection rate was almost similar in both the genders and predominant in those with a clinical diagnosis of seizure disorder (47.88%). The EEG abnormality detection rate was significant in those referred from the Department of Psychiatry and Paediatrics. Conclusion: : EEG is a relatively inexpensive and non-invasive test for detection of electrical activity in the brain. Though requested for seizure or related disorders, it can also find its place in organic pathology, monitoring treatment response among others.


INTRODUCTION
Electroencephalography (EEG) is the recording of electrical activity produced by the firing of neurons within the brain which is recorded for about 20 to 40 minutes from multiple electrodes placed on the scalp.It is one of the tools to assess cerebral function which is based on the work by Hans Berger in the 1930s. 1 The main use of this noninvasive test is in epilepsy to detect seizure activity, a common problem with estimated worldwide prevalence of 5-30 persons per 1000. 2 The other applications are in the diagnosis of coma, encephalopathy, and brain death. 3It is also used in sleep studies and monitoring seizure during Electroconvulsive Therapy (ECT).Though gives a measure of cerebral function, the role of EEG in organic conditions is limited with the advent of newer imaging modalities like CT and MRI.The use of this neurophysiological tool has been minimum in psychiatry despite the known relationship between epilepsy and psychosis and other psychiatric manifestations, especially with the temporal lobe abnormalities. 4 Patients are sent for EEG for various reasons, usually for seizure, pseudo seizure, organicity and psychosis.There is a paucity of reported literature on EEG findings although many institutes conduct EEG in Nepal now.The current study was conducted in Patan Academy of Health Sciences (PAHS), a tertiary care health sciences center at Lalitpur, Nepal which started its EEG services from 2014.It aims to bridge the current knowledge gap and explore the EEG findings among different cases requested for EEG and their associations.

MATERIAL AND METHOD
This is an analytical retrospective study conducted at the Department of Psychiatry, PAHS of 18month (Ashadh 2072 to Poush 2073) The patients requested for EEG underwent a routine non-sleep deprived EEG using the international standardized 10-20 system of electrode placement.Photic stimulation and hyperventilation methods were used during the EEG recordings where age was not a barrier.All EEGs were done by one technician with the same EEG machine (16

RESULT
The demographic characteristics are given in (Table 1).The majority of the patients belonged to the age group 11-20 years, comprising 29.87% (49) of the total study population.The median age was 19 years with an interquartile range of 17.50.Males were slightly more (51.2%)than females.Most of the patients (36%) did not have any clinical diagnosis mentioned at the time of requesting for EEG.Those diagnosed with seizure disorder (31.7%) were the second highest among those referred for EEG evaluation.The reason for referral for EEG was the exclusion of seizure disorder in the majority of cases (80.5%).More than half (58.5%) of the EEGs were requested by the department of Psychiatry and 15.9% of the EEG requests did not contain the details of the referring departments.Table 2 illustrates the findings of EEG where the abnormality was seen in 43.3% (71).Among them, 26.21% (48) had generalized epilepsy and 14.02% (23) had localization related epilepsy.The most common abnormal pattern in EEG was slow wave (46.2%) and the location was generalized (29.3%) followed by frontal lobe (5.5%).On further analysis of the patients with abnormalities in EEG, most of them belonged to the age group of 1-10 years with the median age of 14 years.The logistic regression model, used to predict the effect of age on the likelihood that the patients develop abnormal EEG, was statistically significant χ2(1) = 5.125, p = 0.024.The model explained 41.0% (Nagelkerke R2) of the variance in EEG abnormality and correctly classified 68.9% of cases.Increasing age was associated with a decreased likelihood of having EEG abnormality with odds ratio 0.976 (95% CI 0.954 -0.998) p = 0.030.The patients who had abnormal EEG were younger overall (mean age 18.91 years vs 24.24 years).and Pediatricians (33.8%) (χ(1)=20.152,p = 0.000) had abnormal EEG with statistically significant associations.(Tables 3 and 4).

DISCUSSION:
Since seizure is more common in a younger age in developing countries and EEG is requested mostly for the exclusion of seizure, this might explain the reason for EEG referral for age group distribution in our study. 5[9][10] Studies suggest male at higher risk for seizure and epilepsy. 5This explains the higher proportion of male in our study for EEG evaluation which was supported by different studies. 7,10Compared to our study (43.3%), the study by Shrestha et al had more EEG abnormality (58.3%). 7The major abnormality pattern in EEG in our study and Molokomme was slow waves 10 .However, spike and wave where reported in Chowdhary et al.as common EEG pattern. 8he majority had EEG abnormality in our study and that of Shrestha et al. 7 However, Bhagat et al reported normal EEG in the majority which was done among the epileptics. 9This difference is expected as EEG is a cross sectional record of the brain activity and 50% of patients with epilepsy can have normal EEG, and therefore, does not exclude epilepsy. 12he seizures were not classified during the time of referral in the studies.Nevertheless, in our study (as per EEG diagnosis) and that of Bhagat et al generalized epilepsy were comparatively more than localized epilepsy. 9On the contrary, a study from Bangladesh reported more localization related epilepsy than generalized. 84][15][16] The disparity between the seizure types clinically and as per EEG could be the misdiagnosis of secondary generalized seizure with generalized tonic clonic seizure and lack of adequate For the prediction of abnormality in EEG, more variables and their association with seizure/organicity need to be looked into.

LIMITATIONS:
The clinical details of the patients referred for EEG were not available.

REFERENCES:
1 channels RMS digital).Wilk normality test.A binary logistic regression was performed to ascertain the effect of age on the likelihood that patients have abnormal EEG.A p value of less than 0.05 was considered significant.