Seizures

I. Background
A seizure is the manifestation of a transient, uncontrolled, synchronous discharge of a population of neurons in the cerebral cortex. Some seizures occur as a symptom during the course of an acute neurologic or medical illness; they do not recur after the underlying disorder has resolved. Epilepsy is a chronic disorder characterized by recurrent seizures that are typically unprovoked and unpredictable.
II. Pathophysiology
A. Etiology
Most cases of epilepsy are idiopathic. Some causes of epilepsy can be a result of trauma, tumors, perinatal encephalopathy, congenital brain malformations, inborn errors of metabolism, genetic syndromes, central nervous system infections, stroke, and neurodegenerative disorders. Epilepsy tends to have age patterns that reflect underlying causes. A higher proportion of epilepsy in children is idiopathic or due to congenital brain malformations or developmental neurologic disorders than in older age-groups. The older the patient, the more likely it is that the cause is a cerebrovascular, neurodegenerative, or neoplastic disorder. The following medical disorders are known to cause nonepileptic seizures: hypocalcemia, hyponatremia, disorders of porphyrin metabolism, cerebral anoxia, nonketotic hyperglycemia, and advanced renal failure. High fever, drug reactions, and withdrawal states can also cause seizures.
B. Epidemiology
The prevalence of epilepsy is in the range of 5 to 10 per 1,000. Age-specific incidence rates have changed, with a decrease in younger age-groups and an increase in persons older than 60 years (1).
III. Evaluation
A. History
Care should be taken to elicit risk factors for seizures pertinent to the patient's age (including a family history of seizures), possible seizure precipitants (medication, alcohol or drugs of abuse, sleep deprivation, strong emotion or stress, intense exercise, flashing lights, fever, or menses), and the clinical features, setting, chronology, and duration of the seizure. In many cases, information about the seizure must be obtained from a witness because the patient may lose awareness or consciousness. The following questions are especially important in determining the etiology of the seizure:
  • Was there an aura?
  • Was there a fall or injury?
  • Was there a loss or impairment of consciousness?
  • Was there staring, eye blinking, vocalizations, or automatisms (repetitive purposeless movements such as lip smacking, chewing, or facial grimacing)?
  • Was there loss of bowel or bladder continence?
  • Was there rhythmic muscular jerking and/or rigidity?
  • Was there a postictal period?
B. Physical examination
The examination is usually normal in patients with epilepsy but occasionally some signs of trauma, an underlying systemic or neurologic disorder, or stigmata of chronic alcoholism may be evident. Additionally, it is important to look for cutaneous manifestations of some genetic disorders (facial nevus flammeus of Sturge-Weber syndrome, adenoma sebaceum of tuberous sclerosis, or café au lait macules and cutaneous neurofibromas of neurofibromatosis).
C. Testing
Laboratory studies in adults and children should be ordered on the basis of suggestive historical or clinical findings. In children with a first simple febrile seizure (<10 minutes, isolated, generalized), laboratory testing should be directed toward identifying the cause of the fever. Studies that may be appropriate for evaluation of a first seizure include a complete blood count, glucose, electrolytes, calcium, magnesium, renal, liver and thyroid function tests, and drug and heavy metal toxicology screening (if there is a question of substance abuse or possibility of exposure).
  • A lumbar puncture should be performed if there is a concern about meningitis or encephalitis or if the patient is immunocompromised. The American Academy of Pediatrics suggests that a lumbar puncture be "strongly considered" when a febrile seizure occurs in an infant younger than 12 months of age or all children on prior antibiotic treatment, "considered" in infants 12 to 18 months of age, and "recommended" if meningeal signs are present in infants older than 18 months of age (2). If increased intracranial pressure is suspected, the lumbar puncture should be preceded by computed tomography (CT) scan or magnetic resonance imaging (MRI) of the head.
  • An electroencephalogram (EEG) is essential in the evaluation of epileptic seizures. An abnormal EEG may confirm the diagnosis but a normal or nonspecifically abnormal EEG does not rule out epilepsy. Sleep deprivation and provocative measures such as hyperventilation and photic stimulation may increase the yield of an EEG.
  • Neuroimaging is often necessary to rule out a structural lesion of the brain. A brain MRI is more sensitive than a CT scan; however, the latter may be appropriate in emergency situations or if an MRI is unavailable or contraindicated. An EEG and neuroimaging need not be performed in the evaluation of an otherwise neurologically healthy child with a simple febrile seizure.
IV. Diagnosis
A. Differential diagnosis
A variety of events, either physiologic or psychogenic, can often be mistaken as seizures. These include syncope, complex migraines, breath-holding spells, transient ischemic attacks, sleep disorders (parasomnias, narcolepsy), transient global amnesia, movement disorders, and psychiatric disorders (panic attacks, anxiety with hyperventilation, dissociative states, psychogenic seizures).
B. Clinical manifestations
The clinical expression of a seizure depends on the location and extent of propagation of the discharging neurons.
  • Partial seizures A partial (focal) seizure begins in a localized area of the cortex. Partial seizures are subdivided into simple partial or complex partial seizures based on the impairment of consciousness (no impairment in simple partial seizures). The signs and symptoms of a partial seizure depend on the cortical region involved and may range from a subjective perception (aura) to motor, autonomic, somatosensory, or psychic phenomena. A complex partial seizure implies spread of the seizure discharge to allow impairment of consciousness. Patients with complex partial seizures usually exhibit automatisms or some other complex motor activity that is not directed or purposeful. A simple partial seizure may evolve into a complex partial seizure, and both may evolve into a generalized seizure.
  • Generalized seizures A generalized seizure involves both the cerebral hemispheres at the onset. Generalized seizures begin with an abrupt loss of consciousness (except myoclonic seizures). Subdivisions of generalized seizures are based mainly on the presence or absence and character of ictal motor manifestations: absence (eyelid fluttering, no loss of postural tone, staring), tonic-clonic (muscular rigidity followed by rhythmic muscular jerking), tonic, clonic, atonic (sudden collapse due to loss of postural tone), myoclonic (sudden, brief muscle contractions affecting any group of muscles).
References
1. Sander JW. The epidemiology of epilepsy revisited. Curr Opin Neurol 2003;16(2):165 - 170.
2. American Academy of Pediatrics. Practice parameter: the neurodiagnostic evaluation of the child with a first simple seizure. Pediatrics 1996;97(5):769 - 772; discussion 773 - 775.