INTRODUCTION

• What is the difference between a seizure and epilepsy?

  • A seizure is a sudden, uncontrolled electrical disturbance in the brain.

  • Epilepsy is a condition in which a person has a risk of recurrent seizures due to a chronic, underlying process.

• Epilepsy is a clinical syndrome with many causes and predisposing factors

• Some causes of epilepsy are epilepsy syndromes in which clinical and pathologic characteristics are distinctive and suggest a specific aetiology

CLASSIFICATION OF SEIZURES

• Seizures are classified based on the guidelines by International League Against Epilepsy (ILAE) Commission on Classification and Terminology

  • This classification is based on clinical features and EEG findings

• Fundamentally seizures are classified into:

  • Focal seizures → originate within networks limited to 1 brain region

  • Generalised seizures → originate and rapidly spread to networks across both cerebral hemispheres

FOCAL ONSET SEIZURES

• Focal seizures arise from a neuronal network that is localised to a single region or is wide spread but is still contained within a single hemisphere

• Previously focal seizures were sub-classified into simple and complex seizures based on the consciousness. But this terminology has been eliminated

• Current classification of focal seizures is based on:

  • consciousness level → impaired or intact

  • nature of onset → motor or non motor

• EEG

  • in partial seizures it may be normal or may show brief discharges → epileptiform spikes or sharp waves

  • focal seizures can arise from the medial temporal lobe or inferior frontal lobe (i.e., regions distant from the scalp), the EEG recorded during the seizure may be nonlocalizing.

Focal Seizures with Intact Awareness

• Focal seizures with intact awareness can present as:

  • Motor - tonic, clonic, myoclonic movements

  • Non motor - sensory, autonomic, emotional

• Features of focal motor seizures are

  • JACKSONIAN MARCH ⇒

    • Some seizures start in very restricted regions like the fingers and progress (over seconds to minutes) to include a larger portion of the extremity.

    • This represents the spread of the seizure activity over a larger region of the motor cortex.

  • TODD'S PARALYSIS ⇒

    • localised paresis in the involved area following the seizure → may last for minutes to hours.

  • EPILEPSIA PARTIALIS CONTINUA ⇒

    • rarely, seizures continue for hours or days → often is found to be refractory to medical therapy

• Non motor focal seizures

  • Focal seizures with intact awareness may also manifest as changes in

    • somatic sensation → paresthesias

    • vision → flashing lights or formed hallucinations

    • equilibrium → sensation of falling or vertigo

    • autonomic function → flushing, sweating, piloerection

  • some patients described internal feelings such as fear, sense of impending change, detachment, depersonalization, deja vu, micropsia, macropsia ⇒ these subjective internal feelings are called AURAS

Focal Seizures with Impaired Awareness

• Focal seizures may also present with the patient's inability to maintain normal contact with the environment

• Patients are typically unable to respond properly to visual or verbal commands

• Frequently, these seizures begin with an Aura → ictal phase starts with a motionless stare

• AUTOMATISMS → involuntary, automatic behaviours that have a wide range of manifestations

  • eg- chewing, lip smacking, swallowing, picking movements

• Usually there is some post ictal confusion that is present and complete recovery may take up to few days

• Other post ictal complications

  • anterograde amnesia may be present

  • transient neurological deficits - aphasia, hemineglect, visual loss

  • post ictal inhibition of the cortical regions that caused the seizures.

EVOLUTION OF FOCAL SEIZURES TO GENERALISED SEIZURES

• Focal seizures can spread to involve both cerebral hemispheres and produce a generalised seizure

• This phenomenon is commonly seen in seizures originating in the frontal lobe

• It is difficult to differentiate a partial seizure which becomes generalised and a GTCS → mostly because on giving history, the bystanders tend to focus on the tonic clonic movements

  • EEG studies can distinguish between the two.

  • Distinction is really important because the further evaluation and treatment of seizures is different for the two types of seizures.

GENERALISED ONSET SEIZURES

• These seizures start at some point in the brain but rapidly involve networks in both cerebral hemispheres

• The following are a few subtypes of generalised onset seizures.

Typical Absence Seizures

• These seizures are characterised by sudden brief lapses of consciousness WITHOUT loss of postural control.

• It usually last for only a few seconds → consciousness returns as suddenly as it was lost

• There is usually no post ictal confusion

• Absence seizures are usually accompanied by subtle, bilateral motor signs such as rapid blinking of the eyelids, chewing movements, or small-amplitude, clonic movements of the hands.

• Some of these typical absence seizures are genetically determined

  • seen in childhood 4-10 years of age or early adolescence

  • may have 100s of seizures per day → child maybe unaware or unable to convey them

  • may present as frequent day dreaming and a decline in scholastic performance

• EEG

  • hallmark of absent seizures → generalised symmetric 3Hz spike-and-slow wave discharges that begin and end suddenly

  • HYPERVENTILATION can provoke these changes and the absence seizure as well → used as a tool in EEG recording

Atypical Absence Seizures

• Characterised by lapse or loss of consciousness which is a lot longer and less abrupt in onset and cessation than typical absence seizures

• Also associated with more obvious motor signs → may include focal localizing signs

• EEG

  • generalised slow spike and slow wave pattern → frequency of 2.5Hz

• Associated with diffuse of multifocal structural abnormalities of the brain

• Less responsive to anticonvulsants

Generalized Tonic Clonic Seizures

• This is the most common seizure type resulting from metabolic derangements → frequently encountered in many settings

The onset is abrupt and without warning

• Some patients have vague premonitory symptoms in the hours before the seizure → AURA

Clinical Phases of GTCS

• Tonic contractions

  • respiratory and laryngeal muscle contraction → respiratory cry

  • respiration is impaired + secretions pool in the oropharynx → cyanosis develops

  • jaw muscle contraction → tongue bite

  • sympathetic tone increase → increase in heart rate, blood pressure and pupillary size

• Clonic phase

  • superimposition of periods of muscle relaxation over the tonic muscle contraction.

  • the periods of rest in between keep increasing until the seizure activity stops → usually does not last more than 1 minute

• Post ictal phase

  • characterised by unresponsiveness, muscular flaccidity, and excessive salivation → stridorous breathing and partial airway obstruction

  • bladder or bowel incontinence

  • consciousness is regained within minutes to hours → but may be associated with postictal confusion

EEG

• Tonic phase - progressive increase in generalised low-voltage fast activity, followed by generalised high-amplitude, polyspike discharges

• Clonic phase - high-amplitude activity is typically interrupted by slow waves to create a spike-and-slow-wave pattern

• Postictal waves - diffuse suppression of all cerebral activity, then slowing that gradually recovers as the patient awakens.

Atonic Seizures

• Characterised by sudden loss of postural muscle tone lasting 1-2s.

• Consciousness is very briefly impaired and there is usually no post ictal confusion

• Clinically it may present as a quick head drop or nodding movement → dangerous because it can cause trauma

• EEG - spike and wave discharges followed by slow waves which correlate with muscle tone

• Commonly seen in association with epilepsy syndromes

Myoclonic Seizures

• Myoclonus → sudden and brief muscle contraction that may involve one part of the body or the entire body

• Normal physiologic myoclonus → sudden jerking movements observed while going to sleep

• Pathologic myoclonus is seen in:

  • metabolic disorders

  • degenerative CNS diseases

  • anoxic brain injury

• Myoclonic seizures → are true epileptic events that are caused by cortical dysfunction

• EEG → bilaterally synchronous spike and slow wave discharges immediately prior to the movement

• Predominantly a part of juvenile myoclonic epilepsy.

Epileptic Spasms

• These are brief sustained flexion or extension of proximal> distal muscles

• EEG -

  • Hypsarrythmias → diffuse giant slow waves with a chaotic background or irregular multifocal spikes

  • during the episode, there is a decrease in the background waves → Electrodermal response

• EMG → rhomboid shape which can help differentiate between muscle spasm and tonic and myoclonic seizures

• Occurs predominantly in infants.

Check out more about EEGs in the following articles:

• Understanding the basics of Electroencephalogram

• The wave - Characteristics of an EEG

• Anatomical basis of EEG