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Year : 2016  |  Volume : 9  |  Issue : 1  |  Page : 51-54  

Spectrum of electroencephalographic abnormalities in a cohort of patients from a teaching tertiary care hospital in Western India

1 Department of Neurology, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr DY Patil Vidyapeeth, Pimpri, Pune, Maharashtra, India
2 Department of Medicine, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr DY Patil Vidyapeeth, Pimpri, Pune, Maharashtra, India

Date of Web Publication22-Dec-2015

Correspondence Address:
Piyush Ostwal
601, N4, Nakshatram, Premlok Park, Chinchwad, Pune - 411 033, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0975-2870.172429

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Context: Electroencephalogram (EEG) is a very important tool for investigation of the central nervous system as it provides information about the function of neurons at the time of recording. The major utility of EEG is in the detection of abnormal, excessive electrical activity seen in patients with seizures. Aims: To determine the prevalence of abnormality on EEG in our patient population and to assess the contribution of EEG as a diagnostic modality in a multispecialty hospital. Materials and Methods: EEG findings of 107 patients (age 187 ± 80 months) who underwent EEG for various indications was analyzed. Results: It was found that 20 (18.69%) patients had abnormal EEG. The abnormalities included spikes (50%), sharp waves (50%), spike and wave discharges (20%) and the background abnormalities. Conclusions: The yield of EEG was lower in our study as compared to some other studies. The possible reason may be a higher proportion of patients with febrile seizures and unselected patient population.

Keywords: Electroencephalogram, epilepsy, spike

How to cite this article:
Ostwal P, Dabadghao VS. Spectrum of electroencephalographic abnormalities in a cohort of patients from a teaching tertiary care hospital in Western India. Med J DY Patil Univ 2016;9:51-4

How to cite this URL:
Ostwal P, Dabadghao VS. Spectrum of electroencephalographic abnormalities in a cohort of patients from a teaching tertiary care hospital in Western India. Med J DY Patil Univ [serial online] 2016 [cited 2020 Aug 5];9:51-4. Available from:

  Introduction Top

A seizure is defined as a transient occurrence of signs and/or symptoms due to the abnormal excessive or synchronous neuronal activity in the brain. [1] It is one of the most common entities encountered by neurologists in the emergency and outpatient setting. In an Indian study, the estimated prevalence and average annual incidence rate was 572.8 per 100,000 and 27.27 per 100,000 per year, respectively. [2]

Electroencephalogram (EEG) records the electrical activity of the neurons and has a good temporal resolution. The pattern of discharges and their location can help in defining the type of epilepsy in a given patient. The aim of our study was to determine the prevalence of EEG abnormalities in our patient population and to assess the contribution of EEG as a diagnostic modality in a multispecialty hospital.

  Materials and Methods Top

This was a cross-sectional study carried out in the Department of Neurology at Dr. D. Y. Patil Medical College, Hospital and Research Centre, Pimpri, Pune, Maharashtra, India. The patients were referred to the EEG laboratory from the clinical departments for various diagnoses. They were advised to wash hair with shampoo and not to apply oil. Each recording of EEG was obtained through digital equipment with a minimal duration of 20-30 min and electrode positioned on the scalp according to international 10-20 system. Recording was done in both awake and sleep state, except those who didn't sleep, only awakened state recording was taken. Provocative stimuli of hyperventilation for 3 min and photic stimulation were given. The EEG was interpreted by consultant neurologist, trained, and experienced in electrophysiologic studies. The EEGs done between October 2012 and December 2013 were included for the purpose of this study. The EEG was examined for abnormality in the background or epileptiform discharges. The background activity was classified as normal (organized and symmetrical) or abnormal (disorganized and/or asymmetrical). The abnormal EEG activity was also classified as generalized or focal. The presence, morphology and localization of bursts of slow waves, and epileptiform paroxysms were evaluated. The latter was classified as a spike, sharp wave, polyspikes and spike and wave complexes. The data collected were summarized using descriptive statistics.

  Results Top

A total of 107 patients underwent EEG for various indications. The patients were referred to the EEG laboratory from the departments of pediatrics, internal medicine, and psychiatry. The EEGs were performed between October 2012 and June 2013. Of the 107 patients, 65% were males and 35% were females [Figure 1]. The mean age of the patients who underwent EEG was 187 ± 80 months. Sixty-four (59.8%) subjects belonged to pediatric age group (age of ≤144 months). Most of the patients were referred with diagnosis of generalized tonic-clonic seizure (GTCS) (43%) followed by febrile seizure (20.6%), focal seizure (5.6%), and nonepileptic indication (14%). Among pediatric and adult age groups, GTCS was the most common referring diagnosis for EEG [Table 1]. In pediatric group, febrile seizure was the next common indication. The major indications for EEG in nonepileptic adult patients were psychiatric conditions such as alcohol withdrawal and psychosis and in pediatric patients, it was mainly breath holding spells.
Figure 1: Graph showing gender distribution of patients

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Table 1: Correlation of referring diagnosis with age

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Pediatric group formed a major chunk of abnormal EEGs (65%). Among abnormal EEGs, the major referring diagnosis was GTCS (60%) [Table 2]. There was no significant difference between the proportion of abnormal EEGs between adult and pediatric population among the whole study population and among GTCS patients. The clinician's referring indication was missing for 15.9% patients. It was found that 20 (18.69%) patients had abnormal EEG [Figure 2]. Sixteen (15%) patients had epileptiform discharges of which 7 had generalized, and 9 had focal discharges [Figure 3]. The epileptiform discharges included spikes (10), sharp waves (10) and spiked and wave discharges (4). Five (5%) subjects had abnormalities of the background.
Figure 2: Graph showing proportion of electroencephalogram with abnormal findings

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Figure 3: Electroencephalogram record showing spike and wave complexes in a frontocentral predominance at fifth second (sensitivity 10 ìv/mm, sweep 30 mm/s)

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Table 2: Correlation of referring diagnosis with age among patients with abnormal EEGs

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  Discussion Top

Since seizures are manifestations of the abnormal electrical activity of the brain, therefore EEG becomes a natural adjunct in the evaluation of patients with a seizure. The major utility of EEG lies in the fact that it is a temporal record of the electrical events going on in the brain as against imaging modalities which define the anatomy of the brain. Together they help clinicians in determining patient's problem and in offering appropriate treatment. Hans Berger first reported his EEG findings in 1929 and since then the technique and understanding of EEG have advanced considerably. The availability of EEG in digital format for recording and reporting has brought a whole new dimension to the identification of abnormalities. The uses of EEG in the practice of epilepsy includes confirmation of an attack being seizure, the determination of focality, syndromic classification of epilepsy, predicting the risk of recurrence following first unprovoked seizure and following the discontinuation of medications, the diagnosis of nonconvulsive status of epilepticus and in evaluation of a patient for epilepsy surgery. Apart from epilepsy, EEG can be helpful in the evaluation of metabolic encephalopathies, herpes simplex encephalitis, and other disorders of acute change in mental status. [3]

The abnormalities were in the form of epileptiform discharges, and background changes were found in 20 (18.69%) patients. A recent similar study revealed an abnormality in 62.7% of EEGs. [4] Earlier larger studies have reported the incidence of interictal EEG abnormalities in 29-55% on first EEG. [5],[6],[7] The well-established factors affecting the yield of EEG include age of the patient (more often recordable in children), focus of origin (interictal epileptiform discharge [IED] more often in temporal lobe seizures), and medications (antiepileptics reduce discharges). [3] The yield of EEG increases with serial EEGs and up to 90% of patients with epilepsy have been demonstrated to have abnormality by fourth EEG. [7] Sleep deprivation before recording, [8] sleep during record, [9] photic stimulation, [10] and hyperventilation [11] are other techniques which have been shown to increase the likelihood of recording the IEDs. We have employed hyperventilation and photic stimulation as a routine procedure in our EEG recordings.

The prevalence of EEG abnormality in our study is lower as compared to some of the previous studies. The possible reason may be that the patients were not routinely evaluated by a neurologist before referring for EEG. As is common in resource-limited setting like in our country, the neurologists' job is to report the EEG and often the clinical details are lacking. In our study, the data about the indication for EEG lacked in 15.9% of patients. There may be patients who have been referred for EEG with diagnoses like vertigo. Also, a significant proportion of pediatric patients were referred for febrile seizures, which again may have reduced the positive yield of EEG. The limitation of our study is that it was a retrospective analysis and hence, the detailed clinical information was not available.

  Conclusion Top

EEG remains the cornerstone in the evaluation of patients with seizures. The functional information provided by EEG used in conjunction with imaging modalities can help the clinician in taking the management decisions. The positive yield of EEG may vary at different laboratories in accordance with the referral base of the center. Evaluation and selection by a neurologist may probably increase the positive yield of EEG. Whether the training and experience of the neurologist reporting the EEG and technologist recording it has any effect on the detection of abnormalities is a field of further research.


We are thankful to Mrs. Veena Nair for the technical assistance in the data collection for this work.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Fisher RS, van Emde Boas W, Blume W, Elger C, Genton P, Lee P, et al. Epileptic seizures and epilepsy: Definitions proposed by the International League Against Epilepsy (ILAE) and the International Bureau for Epilepsy (IBE). Epilepsia 2005;46: 470-2.  Back to cited text no. 1
Banerjee TK, Ray BK, Das SK, Hazra A, Ghosal MK, Chaudhuri A, et al. A longitudinal study of epilepsy in Kolkata, India. Epilepsia 2010;51:2384-91.  Back to cited text no. 2
Walczak TS, Jayakar P, Mizrahi EM. Interictal electroencephalography. In: Engel J, Pedley TA, editors. Epilepsy: A Comprehensive Textbook. 2 nd ed. Philadelphia: Lippincott Williams & Wilkins; 2008. p. 810-25.  Back to cited text no. 3
Chowdhury RN, Hasan AH, Rahman KM, Mondol BA, Deb SR, Mohammad QD. Interictal EEG changes in patients with seizure disorder: Experience in Bangladesh. Springerplus 2013;2:27.  Back to cited text no. 4
Marsan CA, Zivin LS. Factors related to the occurrence of typical paroxysmal abnormalities in the EEG records of epileptic patients. Epilepsia 1970;11:361-81.  Back to cited text no. 5
Goodin DS, Aminoff MJ, Laxer KD. Detection of epileptiform activity by different noninvasive EEG methods in complex partial epilepsy. Ann Neurol 1990;27:330-4.  Back to cited text no. 6
Salinsky M, Kanter R, Dasheiff RM. Effectiveness of multiple EEGs in supporting the diagnosis of epilepsy: An operational curve. Epilepsia 1987;28:331-4.  Back to cited text no. 7
Fountain NB, Kim JS, Lee SI. Sleep deprivation activates epileptiform discharges independent of the activating effects of sleep. J Clin Neurophysiol 1998;15:69-75.  Back to cited text no. 8
Niedermeyer E, Rocca U. The diagnostic significance of sleep electroencephalograms in temporal lobe epilepsy. A comparison of scalp and depth tracings. Eur Neurol 1972;7: 119-29.  Back to cited text no. 9
Wolf P, Goosses R. Relation of photosensitivity to epileptic syndromes. J Neurol Neurosurg Psychiatry 1986;49: 1386-91.  Back to cited text no. 10
Sato S, Dreifuss FE, Penry JK, Kirby DD, Palesch Y. Long-term follow-up of absence seizures. Neurology 1983;33: 1590-5.  Back to cited text no. 11


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2]


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