Introduction

What is epilepsy? 

The International League Against Epilepsy (ILAE) has defined epilepsy as "a condition characterised by two or more recurrent epileptic seizures over a period longer than 24 hours, unprovoked by any immediate identified cause". 

What is temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is a neurological condition, in which repetitive seizures begin in the temporal lobe. It is the most prevalent form of focal epilepsy, usually with aura, automatisms, and impaired awareness.¹

Pathophysiology

The temporal lobes are the most epileptogenic region of the brain, mainly due to the fact that they are most often the location of seizure-provoking insults, such as hypoxia and head injury.

Histologically, neuronal loss – especially that of pyramidal cells – occurs in certain subregions of the hippocampus. This is followed by astrocyte proliferation, which provides the foundation for scarring. These morphological alterations are believed to lead to epileptic networks of cells.²

Basics of EEG

Role of Electroencephalography (EEG) in epilepsy diagnosis

TLE is diagnosed by a history of characteristic partial seizure symptoms. The diagnosis is confirmed by the capture of a typical episode during an electroencephalogram (EEG) or video-EEG, with epileptiform activity over one or both temporal regions. Video-EEG monitoring has revolutionised diagnosis and should be considered in patients in whom diagnosis is uncertain.³

Types of EEG

From an EEG analysis standpoint, we opine that EEG can be divided into the following three categories.

• A time-invariant EEG is what one calls an EEG where the brain's functional state does not change over a period of time. In a time-invariant EEG, there is no noticeable change in the brain's state throughout the capture process, for example, a resting-state EEG without psychological activity. Alternatively, some changes in brain characteristics are not included among the main features to be studied. For example, in epilepsy research, researchers pay more attention to the pathological EEG. In this case, the interictal period without epileptic discharge can also be considered a time-invariant. EEG is in a stable state for a long time. While the EEG is unstable, there exist relatively stable segments of data within the unstable EEG if these two segments are analyzed
• Reliable event-related: EEG can be thought of as a generalization of event-related potentials. These are certain points of interest that show the brain's response to certain stimuli, such as visual, auditory, or motor events
• Random event-related EEG refers to an EEG caused by a particular event where the event's induction time is random and cannot be estimated

In the study of such diseases as epilepsy or Parkinson's disease, pathological EEG is evoked by abnormal brain activity in the area of the lesion, but the pathological induction time is difficult to determine, leading to a time-varying EEG.⁴

EEG findings

Interictal EEG discoveries

Epileptiform discharges

These are classical signs of epilepsy and consist of spikes, sharp waves, and spike-and-wave complexes. These are abrupt transient departures from the normal pattern of EEG.

Focal epileptiform discharges

Focal or localised abnormalities implicating focal epilepsy. The profile of these discharges depends upon the lobe of origin

Frontal Lobe: Invariably has multicentric and atypical patterns that may consist of focal spikes or sharp waves.

Temporal lobe

Can exhibit rhythmic theta or delta activity and interictal spikes, frequently noted in mesial temporal structures.

Occipital lobe

It is identified by occipital spikes, which can be related to visual impairment.

Generalised Epileptiform Discharges: These are generalised spike-and-wave or polyspike-and-wave discharges, which are typical in idiopathic generalised epilepsies.^5,6,7

Limitations of EEG

Although EEG is incredibly helpful for diagnosing TLE, it is not without limitations. A normal EEG does not rule out epilepsy since interictal epileptiform discharges are not always present. Additionally, some deep-seated or small cortical lesions may not cause detectable surface EEG abnormalities.⁸

Electroencephalography (EEG) continues to be a mainstay in the management and diagnosis of epilepsy, providing valuable information about brain activity rhythms. Its value in identifying epileptiform discharges, segregating epilepsy categories, and in making treatment planning decisions makes EEG an indispensable ally for clinicians. With the advent of time, improvements in technology have made it much more sensitive, accurate, and clinically valuable, and today it is applied beyond the narrow confines of epileptic diagnosis alone.

Despite its advantages, EEG has limitations, including its inability to capture deep-seated epileptic foci and its reliance on interictal abnormalities that may not always be present during recording. However, innovations such as high-density EEG, machine learning-based analysis, and electrical source imaging (ESI) have enhanced its diagnostic yield. The combination of EEG with other imaging techniques such as magnetic resonance imaging (MRI) and functional imaging has further improved the localisation of epileptogenic areas, especially for presurgical assessment in drug-resistant epilepsy.

One of the most promising new advances in EEG is the investigation of high-frequency oscillations (HFOs), which have become promising biomarkers of epileptogenicity. Furthermore, the use of artificial intelligence (AI) and machine learning in EEG analysis can potentially automate seizure detection, enhance diagnostic accuracy, and tailor treatment strategies. The expanding utilisation of continuous EEG monitoring, particularly in intensive care units, has also facilitated a real-time comprehension of seizure activity and non-convulsive status epilepticus, which has resulted in improved patient outcomes.

As technology improves, the potential for EEG use in the future diagnosis of epilepsy is promising. The availability of portable, wearable EEG machines might allow long-term, real-world seizure monitoring to decrease hospital-based testing dependency. In addition, the incorporation of cloud computing and big data analysis might facilitate mass-scale epilepsy studies, allowing more personalised and efficacious treatment modalities.

Recent advancements in EEG

1. Electrical Source Imaging (ESI): ESI has become a critical presurgical tool for epilepsy evaluations. By precisely localizing epileptogenic regions, ESI aids in better surgical outcomes. Its accuracy and clinical value have been confirmed by recent research, emphasising its use in multimodal evaluations of drug-resistant focal epilepsy
2. High-Frequency Oscillations (HFOs): HFOs, denoted by very fast brain wave patterns, have been studied as possible biomarkers of epileptogenic zones. Although they hold promise for detecting seizure-generating zones, recent studies have prompted further research in order to define their clinical use at the patient level
3. Intracranial EEG (iEEG): The use of iEEG, such as methods like electrocorticography (ECoG) and stereo-electroencephalography (sEEG), has broadened our knowledge regarding brain activity. Systematic reviews have offered templates for iEEG studies, discussing limitations and suggesting guidelines for improving data interpretation and clinical application
4. EEG in Intensive Care: Continuous EEG monitoring in intensive care units has come to play a crucial role in the identification of non-convulsive seizures and other cerebral activity in critically ill patients. Such practice allows early intervention and has been one of the main reasons for the expansion of clinical applications of EEG^9,10 

FAQs

What is EEG, and how does it help in diagnosing epilepsy?

EEG (Electroencephalography) is a test that records electrical activity in the brain using electrodes placed on the scalp. It helps diagnose epilepsy by detecting abnormal brain wave patterns, such as spikes and sharp waves, which are commonly associated with seizures.

Can an EEG confirm epilepsy?

While EEG is a crucial diagnostic tool, a normal EEG does not rule out epilepsy. Some people with epilepsy may have normal EEG results between seizures. In such cases, prolonged EEG monitoring, video-EEG, or repeated tests may be needed for an accurate diagnosis.

What are common EEG findings in epilepsy?

EEG in epilepsy often shows epileptiform discharges, including:

• Spikes and sharp waves (indicating abnormal electrical activity)
• Generalised spike-and-wave patterns (seen in generalised epilepsy)
• Focal epileptiform discharges (seen in focal epilepsy)

How long does an EEG test take?

A routine EEG typically takes 20–60 minutes, but some tests, like prolonged EEG or video-EEG monitoring, can last for hours or days to capture seizure activity.

What are the different types of EEG used for epilepsy diagnosis?

• Routine EEG: Short recording, usually 30–60 minutes
• Prolonged EEG: Extended recording for a few hours or overnight
• Ambulatory EEG: Allows monitoring over days while the patient is at home
• Video-EEG Monitoring: Simultaneous video and EEG recording in a hospital setting to capture seizures

Can EEG detect all seizures?

No, EEG may not always capture a seizure, especially if it occurs deep in the brain where surface electrodes cannot detect it. In such cases, intracranial EEG (iEEG) or repeated tests may be necessary.

Summary

In summary, EEG is still an essential diagnostic tool and management modality for epilepsy. Although there are limitations in conventional EEG, the use of signal processing advancements, artificial intelligence-based analysis, and multimodality integration has greatly enhanced its application. Ongoing research continues to optimize EEG technology, making it likely that it will assume an increasingly dominant position in epilepsy treatment, advancing early diagnosis, maximising treatment protocol, and advancing the quality of life in epileptic patients.