• Clinical science

Focal seizures and syndromes

Abstract

Focal (or partial) seizures are an abnormal activation of neurons confined to one cerebral hemisphere, and are best described according to whether or not consciousness and/or awareness are impaired. In contrast, generalized seizures are characterized by abnormal neuronal activity that quickly spreads to both hemispheres of the brain. Seizures can be caused by genetic abnormalities, structural abnormalities, metabolic disturbances, tumors, or infection. Symptoms depend on the location of the ictal event within the brain and may include clonic movements, as well as sensory and psychiatric symptoms. Focal seizures may involve altered levels of consciousness (complex partial seizures) or evolve to secondarily generalized seizures. Temporal lobe epilepsy is the most common type of focal seizure. It frequently arises from hippocampal sclerosis, but may also be caused by malignancies or infections. Diagnosis of focal seizures begins with electroencephalography and neuroimaging. If an infectious or a metabolic etiology is suspected, laboratory tests can also be helpful. Focal seizures secondary to underlying non-neurologic pathologies (e.g., infection or metabolic disturbances) are treated by correcting the underlying abnormality. Seizures of unknown etiology or from a neurological defect are managed with anti-epileptic drugs such as lamotrigine (first-line), levetiracetam, or phenytoin.

Etiology

  • Focal seizures can be caused by many factors:
    • Genetic
    • Structural and/or metabolic disturbances:
      • Morphologic changes (e.g., hippocampal sclerosis or tumor growth)
      • Electrolyte imbalances
      • Drug intake
      • Infections
    • Unknown
  • Common causes based on age group:
    • Childhood: perinatal injury to the brain
    • Adolescence: encephalitis and cerebral trauma
    • Middle-aged adults: cerebral tumors
    • Adults of advanced age: vascular encephalopathies and vascular dementia

Focal seizures with genetic cause

Benign epilepsy with centrotemporal spikes

  • Definition: a benign form of epilepsy in children, featuring centrotemporal spikes
  • Epidemiology
    • Most common form of epilepsy in children (∼ 10–20% of cases)
    • Peak incidence: 7–9 years
  • Clinical features
    • Usually occurs during sleep
    • Facial twitching or numbness, hypersalivation, and speech arrest (during and frequently even after the event)
    • Involvement of an arm or an entire side of the body is possible, as is secondary generalization.
  • EEG: centrotemporal spikes or sharp waves
    • Often occurs in bursts
    • Often bilateral, in which case activity in one hemisphere may be independent of the other
    • Typical morphology and orientation
      • Biphasic waves of approx. 70–100 ms (spikes) or up to 200 ms (sharp waves)
      • Horizontal dipole: maximum positivity in the frontal region, maximum negativity towards the centrotemporal region
  • Prognosis: usually seizures spontaneously resolve by puberty
  • Treatment:

Rare idiopathic forms

References:[1]

Focal seizures with structural or metabolic cause

Temporal lobe epilepsy

  • Epidemiology: most common form of epilepsy (∼ 40% of all epilepsy cases; ∼ 70% of focal epilepsy cases)
  • Etiology
    • Hippocampal sclerosis
      • In most cases, sclerosis develops in Sommer's sector (region CA1).
      • Found in approx. 70% of patients suffering from temporal lobe epilepsy that is resistant to pharmacotherapy
    • Encephalitis (e.g., herpes simplex encephalitis), developmental disorders, neurodegenerative disorders, tumors
  • Clinical features
    • Seizures commonly occur in clusters, last approx. 30 seconds to 2 minutes, and follow this sequence:
      1. Aura
      2. Focal seizure with impaired awareness (complex partial seizure)
        • Motor symptoms: typically oral alimentary automatisms like lip-smacking; also fidgeting (e.g., with clothing), stretching of the body, or walking in place
        • Autonomic symptoms: tachycardia, urge to void the bladder, mydriasis, sweating, salivating
        • Altered mental status: children appear absent-minded; (e.g., staring ahead, unresponsive when spoken to), but no loss of consciousness or syncope occurs!
        • Less frequently: loss or change in the sense of taste or smell, aphasia
        • Focal seizures may progress to generalized seizures.
      3. Postictal phase with confusion and tiredness is common; transient epileptic amnesia (rare): transient anterograde or retrograde amnesia immediately proceeding or following a seizure
    • The limbic system may be impaired in recurrent uncontrolled seizures.
  • Diagnosis: temporal lobe spikes on EEG
  • Treatment
  • Prognosis: unfavorable (only 40% of patients on pharmacotherapy remain asymptomatic)

Frontal lobe epilepsy

  • Etiology: see “Etiology” above
  • Clinical features
    • Usually simple partial seizures featuring various motor symptoms (muscle tension, vocalization, gaze deviation, or head directed towards the unaffected side )
      • May feature autonomic symptoms (enuresis, salivation), impairment of speech, or attention deficits (staring spells that may appear similar to absence seizures)
      • Jacksonian march: spreading of paresthesia or uncontrolled motor activity from one part of the body to adjacent areas, usually distally to proximally
      • Todd's paralysis: sustained paralysis of the affected limb/area after the seizure
      • Usually a series of short seizures (≤ 30 s) occurring during sleep (which often wake the patient)
      • Secondary generalization is possible.
    • Usually no aura and no postictal period of confusion

Focal seizures that feature Jacksonian marches are termed Jacksonian seizures, regardless of the origin of the seizures.

Parietal lobe epilepsy

  • Epidemiology: 5% of cases of focal epilepsy
  • Etiology: See "Etiology" above.
  • Clinical features

Occipital lobe epilepsy

  • Epidemiology: rare
  • Etiology: See "Etiology" above.
  • Clinical features
    • Simple partial seizures featuring visual hallucinations, gaze deviation, and cortical blindness
    • Transition to temporal or frontal lobe seizures (featuring the respective symptoms) is possible.

In general, patients suffering from partial seizures of structural or metabolic origin should be treated with antiepileptic drugs (e.g., lamotrigine or levetiracetam).

Epilepsia partialis continua

  • Epidemiology: rare
  • Etiology: unspecific; current or past damage to the cortex (e.g., scar tissue, encephalitis, tumors)
  • Clinical features:
    • Clonic muscle activity of a particular region of the body ("partialis"), e.g., the mouth or a finger
    • Symptoms persist for several days ("continua")
    • Might be considered a focal status epilepticus
  • Treatment: treat the underlying condition

References:[2][3][4][5][6][7][8]

Diagnostics

See seizure disorders learning card.

Treatment

See seizure disorders learning card.