Definitions:

  • Seizures
    • occasional, sudden, rapid and local discharges of gray matter
  • Epilepsy
    • brain disorder characterised by periodic, unpredictable occurrence of seizures

Seizures

  • Transient changes of behaviour
    • due to disordered, synchronous  and rhythmic firing at high frequency of groups of neurons from the cerebral cortex
  • When seizure activity is initiated at local focus (cortex, hippocampus, thalamus)
    • invades normal brain tissue to involve both parts of the cerebral hemispheres
    • a generalised convulsion/seizure occur
  • Can be preceded by an aura
    • tingling
    • numbness of limbs
    • hallucinations
  • followed by convulsions
    • involuntary skeletal muscle movements
    • loss of consciousness
  • After an attack
    • post-ictal depression
      • patient is confused, drowsy and has headache
  • Abnormal electrical activity during and after a seizure can be recorded using electrodes placed on the scalp. Called the electroencephalogram (EEG)
    • it shows characterisitic features for various types of seizures
  • Repeated epileptic attacks can cause neuronal death

The symptoms of an epilepsy attack depends on

  • the site of the primary abnormal electrical discharges
  • the extent of their spread

Range of epilepsy attack severity

  • A seizure attack may range from a brief lapse of attention to a full convulsive fit with jerky movements.
  • The patient may become unconscious for a short time, have a change in perception and experience odd sensations or behaviours
  • Others may exhibit repetitive movements like blinking or twitching

When abnormal activities (seizures) involve the:

  • motor cortex
    • convulsions occur
  • hypothalamus
    • peripheral autonomic effects occur
  • reticular formation of the upper brain stem
    • consciousness is lost

Classification of seizure types

Generalised seizures
Seizure activity affect both brain hemispheres

  • Generalized tonic-clonic (grand mal) seizures
    • loss of consciousness
    • tonic muscle contractions
    • alternating with clonic contractions (lasting 1-2 minutes)
  • Absence (petit mal) seizures
    • abrupt onset of impaired consciousness
      • with staring
    • cessation of ongoing activity
      • lasting less than 3 seconds
    • resumption of activity on end of seizure
      • with no awareness of seizure episode
    • 3 Hz spike EEG. related to:
      • Voltage regulated Ca 2+ current / low threshold
        current (T-current)
  • Tonic seizures
  • Atonic seizures
  • Clonic seizures
  • Myoclonic seizures
    • short ( 1 sec) shock-like contraction of muscle
    • may be limited to 1 extremity/generalised

Partial (focal) seizures
seizure activity begins at a focal site in the cortex

  • Simple partial seizures
    • Manifestations depend on the region of cortex activated by the seizure:
      • Motor cortex
        • clonic jerking of left thumb
      • Sensory (somatosensory) cortex
        • paresthesia of left thumb
    • Consciousness retained
  • Complex partial seizures
    • Loss of consciousness lasting 30sec – 2 min
    • Associated with purposeless movements
      • like lip smacking or hand wringing
  • Partial seizures secondarily generalised (tonic-clonic)
    • seizure affecting both brain hemispheres
    • loss of consciousness
    • tonic muscle contractions
      • alternating with clonic contractions
    • lasting 1-2 minutes
  • Psychomotor epilepsy
    • Focus on temporal lobe
    • Stereotype
      • purposive movement
        • rubbing/patting movement
      • behaviour
        • dressing, walking, combing hair
    • Could have strong emotional response
    • Seizure lasts few minutes
      • no awareness of event on recovery
  • Jacksonian Epilepsy
    • focus of abnormal activity in the motor cortex
    • Repetitive jerking of particular muscle group
      • beginning on 1 side of body
      • Thumb / big toe / angle of the mouth spreading to
        involve other parts of the body within 2 min before
        dying out
    • Voluntary control of the affected parts are lost, but consciousness could be retained

Other types of seizures

  • Infantile spasms
  • Febrile seizures
  • Status epilepticus
    • continous seizure episodes
    • life threatening

Implication of knowing types of seizure

  • Importance
    • predicting prognosis
    • selecting treatment
    • likelihood of finding underlying cause of seizure
  • 3 stages to a seizure
    • initiation
    • synchronization of surrounding
    • propagation
      • recruitment of normal neurons

Cause of epilepsy

  • no recognisable cause
  • Develop from brain damage
    • trauma
    • infection
    • tumour growth
    • neurological diseases

Seizure provoking factors

  • Missed medication
  • Sleep deprivation
  • Stress
  • Alcohol & Drug abuse
  • Over the counter medication
  • Nutritional deficiencies:
    • Vitamins and minerals
  • The menstrual cycle
  • Cycles of the moon
  • Bright / flickering light
  • Certain sound

Diagnosis of seizures

  • Patient history
  • Physical examination
  • EEG
    • Read from OLIS
  • Imaging to localise seizure focus
    • CT scan
    • PET
    • MRI

EEG

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  • Electroencephalography (EEG) is a test by which the electrical activity generated by the brain is recorded through thin wires placed on the scalp.
    • Normal brain rhythms and any abnormal epileptic activity are reviewed on a computer screen or on paper.
    • The EEG recording assists in determination of the seizure
      type and epilepsy syndrome.
  • In special circumstances, EEG may assist monitoring of treatment and help localise the seizure focus.
  • EEG should be recorded and interpreted in a centre experienced in management of epilepsies and EEG

Main roles of EEG

  • Help distinguish focal from generalised seizures and epilepsies
  • Help localise the site of seizure activity in a child with focal epilepsy
  • Help make a specific (syndrome) diagnosis
  • Help confirm or exclude epilepsy, following a thorough clinical evaluation
  • Monitor treatment in some types of epilepsy

Brain imaging

  • Structural imaging (CT, MRI)
    • exclude an underlying brain abnormality
      • scar
      • malformation
      • tumour
      • infection
  • Functional imagine (SPECT, PET, fMRI)
    • assist localisation of a seizure focus and its relationship to important brain region
    • usually in children considered for brain surgery

Epilepsy – Impact on patients

  • The young
    • interruption in their studies, activities, family, career
  • Female patients
    • antiseizure drugs on fetal development
      • birth defects (spina bifida, cleft lip etc)
    • antiseizure drugs cause liver enzyme induction
      • failure of oral contraceptives
    • increase risk of bone disease
    • seizures may disrupt functions of estrogen
      • decrease birth rate
      • weight gain
      • abnormal menstrual cycle
      • cyst in ovaries

Neurochemical basis of seizures

  • Seizures associated with
    • (-) inhibitory synaptic function (GABA)
    • (+)excitatory synaptic function (Glutamate)
    • Abnormal electrical properties of affected neurons
  • seizures in experimental animals caused by:
    • GABAa- antagonists (bicuculline, picrotoxin)
    • Agonists of glutamate receptor subtypes (NMDA, AMPA,
      kainic acid)
  • seizures in expt animals alleviated (relieved) by:
    • GABAa- agonists
    • Antagonists of glutamate receptor subtypes (NMDA, AMPA, kinic acid)
  • Post-mortem human brains:
    • (-) glutamate in cells of focus
    • (+) in cells surrounding focus

Antiseizure drugs

  • Prolong sodium channel inactivation
    • phenytoin
    • carbamazepine
    • lamotrigine
    • phenobarbitone
    • sodium valproate
    • topiramate
    • [-] rapid repetitive firing in isolated neurons
  • Reduction of low threshold T-type Ca++ current which govern oscillatory responses in thalamic neurons
    • ethosuximide
  • Enhance GABAA activity to inhibit synaptic transmission:
    • Direct action on GABA receptor-chloride
      channel complex
      • benzodiazepines
      • barbiturates
      • topiramate
    • Block reuptake or metabolism of GABA
      • sod valproate
      • gabapentine
      • tiagabine
      • vigabatrin
  • Reduce Glutamate transmission:
    • Block of AMPA receptors
      • phenobarbitone
      • topiramate

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