EPILEPSY AND SEIZURE DISORDERS

By Dr. J.B. Adetunji

Introduction

• A seizure is a paroxysmal event due to abnormal, excessive, hypersynchronous electrical discharges from neurons in the CNS. The origin and distribution pattern of the electrical discharge determine the manifestations of the abnormality — ranging from convulsive activity to experiential/behavioural phenomena which may not be discernible to an observer.
• Epilepsy is defined as the occurrence of recurrent seizures of spontaneous onset and termination. Epilepsy is not a single disease but made up of a symptom — complex of excitatory brain dysfunction.

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Classification of Seizures

• The classification of seizures requires a good history and EEG investigation and is very useful in characterizing possible aetiologies, selection of appropriate anticonvulsants in addition to providing useful information for prognostic and other therapeutic purposes

ILAE Classification of Seizures

• Partial Seizures
• Simple partial seizures — motor, sensory, autonomic or psychic
• Complex partial seizures
• Partial seizures with secondary generalization
• Primarily Generalized Seizures
• Absence (petit mal)
• Tonic — clonic (grand mal)
• Tonic
• Atonic
• Myoclonic
• Unclassified Seizures
• Neonatal seizures
• Infantile spasms

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• Partial seizures occur in restricted parts of the brain and hence often give rise to aura. If origin is superficial in the brain it is easily picked by EEG. In deep-seated ictal focus extracranial EEG electrodes may fail to pick the disturbance.
• If consciousness is impaired it becomes a Complex Partial Seizure. Partial motor seizures often manifest in the limbs (especially hand) and may expand from a finger to larger areas of the UL — Jacksonian march. A resultant localized paresis of the affected hand is called Todd's palsy. It may last for a few minutes or hours.
• Partial Sensory Seizures may manifest as paraesthesia, visual phenomena — flashing lights, hallucinations, equilibrium changes — vertigo, sensation of falling, Autonomic manifestations include flushing, sweating, piloerection. Simple partial seizures arising from the Temporal or Frontal lobes often have peculiar characteristics like rising epigastric sensations, fear, sense of impending change, depersonalization, déja vuos phenomena, micropsia, macropsia. These often are associated with or precede complex partial and secondary generalization.

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Complex Partial Seizures

• The seizures frequently begin with an aura followed by transient impairment of consciousness. The onset of the ictal phase is often characterized by sudden behavioural arrest of motionless stare accompanied by automatisms — involuntary automatic behaviour of diverse patterns. Patient at this stage has developed amnesia hence are confused post-ictally. Some of the automatisms include chewing, lip smacking, swallowing or occasionally elaborate behavioural pattern.

Generalized Seizures

• These are defined to arise from both cerebral hemispheres simultaneously. The existence of focal origin with rapid spread of electrical activity is difficult to exclude. Generalized seizures may arise from cellular biochemical or structural abnormalities that have a more widespread distribution.

Absence Seizures (Petit mal)

• Characterized by sudden brief lapses of consciousness without loss of postural control. The seizure lasts a few seconds with quick regaining of consciousness and no post ictal confusion. The attacks are often clinically inapparent in spite of the fact that it may occur several hundred times a day. Absence seizures occur mainly in early childhood (4 - 8yrs) or early adolescence. It is important to note that subtle motor changes often accompany absence attacks — bilateral motor signs like rapid blinking of the eyelids, chewing, small amplitude clonic movements of the hands. EEG typically shows 3Hz spike and wave discharges that are bilateral and synchronous and of brief episodes over a normal background. About 70% of patients would experience full recovery during adolescence.

Atypical Absence Seizures

• These differ clinically and electrophysiologically from the typical absence seizure. They are usually due to diffuse or multifocal structural abnormalities of the brain. There are often other features of neurological dysfunction like mental retardation and motor impairment. In addition, response to drug treatment is poor.

Generalized Tonic — Clonic Seizures (grand mal)

This is bilateral, symmetrical and synchronous in manifestation clinically and electrophysiologically. There is no aura though some patients may describe vague premonitory symptoms for some hours preceding attacks.

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• Initial phase - tonic contraction of muscles all over the body; the involvement of the expiratory and laryngeal muscles produces the ictal cry. This contraction also affects the other muscles of respiration resulting in respiratory impairment and copious secretions in the oropharynx with development of cyanosis. Jaw muscle contraction causes tongue and lip bite. A rise in sympathetic tone causes tachycardia, rise in BP and pupillary dilatation.

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• Clonic phase sets in after about 10 — 30 seconds due to the super imposition of periods of muscle relaxation over the tonic contraction. The progressive increase in the duration of muscle relaxation terminates the ictus; this takes 1-3mins.
• Post-ictally, the patient is unresponsive, muscles are flaccid and produce a lot of saliva that may cause partial air way obstruction. Full recovery may take minutes to hours. Post-ictal confusion, headache, fatigue, muscle ache can last for hours. Bowel and bladder incontinence may also occur.

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EEG

• Tonic Phase — generalized low voltage fast activity → high-amplitude polyspikes
• Clonic Phase — high amplitude polyspikes are interrupted by slow waves.
• Post-ictal — diffuse slow waves that improve as patient recovers

Atonic Seizures

• Characterised by sudden loss of postural tone for 1-2secs. This is associated with brief impairment of consciousness. Clinically there may be a head drop in brief attacks while longer ones may result in sudden falls.
• EEG — brief generalized sp-w discharges followed by diffuse slow waves.

Myoclonic Seizures

• Characterised by sudden and brief muscle contraction involving a part of the body-or the whole body.
• EEG — bilateral synchronous sp-w discharges.

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Diagnosis

• History and physical examination
• Investigations
• Full Blood Count
• Blood sugar
• E/U/C
• Skull x-ray
• LP → CSF → M/C/S
• EEG
• CT/MRI
• Findings on MRI/CT
• hippocampal atrophy
• Temporal sclerosis
• Scars
• PET — Positron Emission Tomography
• SPECT — Single Photon Emission Computerized Tomography are useful in refractory seizures.

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Treatment

• Goal is to abolish attacks with minimal side effects
• Monotherapy should be used as much as possible with easy dosing schedule.
• Chronic anticonvulsant therapy or surgery In the event of mass lesion

Drugs In Current Use For The Control Of Seizures

• Valproate
• Carbamazepine
• Phenytoin
• Phenobarbitone
• Primidone
• Clonazepam
• Ethosuximide — absence

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Other drugs

• Gabapentin
• Lamotrigine
• Oxcarbazepine
• Topiramate
• Felbamate
• Pregadaline
• Cannabinol oil – especially in children

Drug Withdrawal

• Treat for at least 3 - 5 seizure free years
• Repeat EEG
• If normal, the patient may be considered for programmed drug withdrawal
• If otherwise continue medication