Seizure Disorder, Focal

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Basics

Description

  • Seizures occur when abnormal synchronous neuronal discharges in the brain cause transient cortical dysfunction.
  • Generalized seizures involve bilateral cerebral cortex from the seizure’s onset.
  • Focal or localization-related seizures have previously been referred to as partial seizures.
  • Focal seizures originate from a discrete focus limited to one hemisphere in the cerebral cortex.
  • Focal seizures are further divided into aware versus unaware and motor versus nonmotor.
  • Presence of impaired awareness is defined as the inability to respond normally to exogenous stimuli due to altered awareness and/or responsiveness:
    • Focal seizures with impairment of awareness (formerly “complex partial seizures”)
    • Focal seizures without impairment of awareness (formerly “simple partial seizures”)

Epidemiology

Prevalence
Focal seizures occur in 20/100,000 persons in the United States.

Etiology and Pathophysiology

  • Focal seizures begin when a localized seizure focus produces an abnormal, synchronized depolarization that spreads to a discrete portion of the surrounding cortex.
  • The area of cortex involved in the seizure determines the symptoms; for example, an epileptogenic focus in motor cortex produces contralateral motor symptoms.
  • In some cases, etiology is related to structural abnormalities that are susceptible to epileptogenesis. Most common etiologies vary by life stage:
    • Early childhood: developmental/congenital malformation, trauma
    • Young adults: developmental, infection, trauma
    • Adults 40 to 60 years of age: cerebrovascular insult, infection, trauma
    • Adults >60 years of age: cerebrovascular insult, trauma, neoplasm
  • A common cause of focal seizure with impaired awareness is mesial temporal sclerosis.

Genetics
Benign rolandic epilepsy, a form of focal seizure disorder, has an autosomal dominant inheritance pattern with penetrance depending on multiple factors.

Risk Factors

  • History of traumatic brain injury (TBI)
  • Children exposed to a thiamine-deficient formula

Commonly Associated Conditions

Epilepsy patients have a higher incidence of depression than the general population.

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