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Epilepsy

Definition

Group of disorders characterised by excessive electrical discharges in the brain, causing discrete symptoms in an episodic manner

 

Risk factors

  • Genetic predisposition
  • Brain injury
  • Low birth weight

 

Differential diagnoses

  • Brain tumour
  • Stroke
  • Brain haemorrhage
  • Syncope
  • Migraine
  • Headache disorder

 

Epidemiology

  • More common in children and adolescents
  • Types of epilepsy vary with age group

 

Aetiology

  • Bursts of increased neuronal discharge
  • Some types can be identified on an EEG
  • May result from a lack of GABA

 

Clinical features

  • Simple = retain consciousness
  • Complex = unconsciousness
  • Generalised = whole body
  • Partial = focal symptoms, only one hemisphere (initially)
  • Absence/petit mal – generalised, simple
    • Brief periods of unresponsiveness, glazed expression, lasts less than 10s
    • Eyelid flutter
    • May have many per day, may be unaware
    • Never result of a tumour
    • May progress to GTCS
  • Generalised tonic-clonic seizure (GTCS) – generalised, complex
    • May have prodrome/aura
    • Tonic stiffening, collapse
    • Clonic rhythmic jerks, generally symmetrical
    • Loss of consciousness, often eyes open, bite tongue, urinary/faecal incontinence
    • Post-ictal phase: flaccid, unresponsive, drowsy, confused, headache, may last a long time, muscle cramps
  • Myoclonic seizure - generalised
    • Brief clonic jerks, commonly experienced by those with other generalised epilepsies
  • Tonic seizures – generalised
    • Stiffening of body, but not followed by clonic jerks
  • Clonic seizure -generalised
    • Involuntary, jerking rhythmic muscle contractions
  • Atonic/akinetic
    • Sudden loss of muscle tone, collapse, loss of consciousness
  • Temporal lobe seizure – partial, can be simple or complex
    • Déjà vu or jamais vu
    • Visual hallucinations
    • Vertigo
    • Panic attack
    • Blank staring
    • GI autonomic symptoms
    • Has post-ictal phase
  • Frontal – partial, can be simple or complex
    • Abnormal body posture
    • Sensorimotor tics
    • Fear
    • Laughing
    • Crying
    • Often during sleep
    • Post-ictal phase is brief, if present at all
    • Usually has prodrome/aura, lasts less than a minute
  • Occipital
    • Visual disturbance

 

Pathophysiology

 

Investigations

  • History
  • EEG

 

Management

  • Calcium channel blockers
    • Ethosuxamide: blocks T type calcium channels, that set the firing rhythm of thalamic relay neurons. Disruption here is associated with absence seizures. Is used for absence seizures. Side effects = nausea, anorexia, lethargy
    • Gabapentin: blocks P/Q type calcium channel, which are the voltage gated channels at synaptic terminals. They allow calcium influx as a result of depolarisation from an action potential. Blocking reduces neurotransmitter release at the synapse. Used in partial seizures. Not severe
  • Sodium channel blockers
    • Block voltage gated sodium channels in neurons, preferentially block closed channels, prolonging their inactive stage. This prolongs hyperpolarisation, and reduces the frequency of APs, and increases the threshold for depolarisation. Are ‘use dependent’ – work best at neurons that fire frequently
    • Carbamazepine – used for all types except absence, especially for temporal, has interactions with other drugs
    • Phenytoin – used for all types except absence, drug interactions and low therapeutic range
    • Lamotrigine – used for all types, especially GTCS. Has no drug interactions and no sedation
  • GABA enhancers
    • GABA is a neurotransmitter that causes inhibition at the postsynaptic membrane, GABA enhancement à decreased neuronal discharge
      • Benzodiazepines (diazepam, lorazepam, clonazepam) increase receptor affinity for GABA, decrease neuronal firing. Used for status epilepticus (IV) and acute seizures. NB – can’t be stopped suddenly as withdrawal makes seizures worse
      • Phenobarbital – increases duration that GABA channels are open. Rarely used. Sedation, depression, drug interactions
      • Vigabatrin – for all types, even resistant
  • Multiple mechanism
    • Valproate is a calcium channel blocker, sodium channel blocker and GABA enhancer. Especially used in infants (low toxicity, no sedation) and mixed types of epilepsy (adolescents). Teratogenic, hepatotoxic, hair thinning

 

Prognosis

Epilepsy.docx
Microsoft Word document [15.7 KB]

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