Etiology

Epilepsy has many possible causes. Seizures result from synchronized electrical activity of neuronal networks in the cerebral cortex. Any disturbance of normal neuronal activity, including injury, infection, and abnormal brain development, can lead to seizures. Cerebral vascular disease is the most common cause in older adults; however, about half of all seizures have no identifiable cause. Seizures may develop because of an abnormality in brain wiring, an imbalance of neurotransmitters, or some combination of these factors. Epilepsy can also be associated with a variety of developmental and metabolic disorders, including cerebral palsy, neurofibromatosis, tuberous sclerosis, and autism.

Typically, seizures are divided into 2 major categories: partial and generalized. Partial seizures occur in only 1 part of the brain and are further divided into simple (without impairment of consciousness) and complex (with impairment of consciousness). Symptoms of simple partial seizures (also called auras) depend on the part of the brain from which the seizures originate and include motor symptoms, sensory symptoms (which can resemble a migraine aura), and even autonomic symptoms. Complex partial seizures are the most common type of seizures in adults with epilepsy. During the seizure, patients may appear to be awake but do not interact with others around them and do not respond normally to instructions or questions. They often stare into space and either remain motionless or engage in repetitive behaviors, called automatisms, such as facial grimacing or gesturing.

Generalized seizures cause impaired consciousness and abnormal activity in both hemispheres at the onset of the seizure. These events may follow partial seizures. They can be nonconvulsive (absence, or “petit mal”) or convulsive (tonic–clonic, or “grand mal”; or some variation of tonic–clonic). Absence seizures almost always begin in childhood or adolescence and are frequently familial, suggesting a genetic cause. During seizures, some patients make purposeless movements, such as jerking an arm or rapidly blinking their eyes. Others have no noticeable symptoms except for brief periods of “absence.” Childhood absence epilepsy often stops when the child reaches puberty. A generalized tonic–clonic seizure is the most dramatic, in that it begins with an abrupt alteration in consciousness, sometimes in association with a scream or shriek. All of the muscles stiffen, and the patient may become cyanotic during the tonic phase. Within a short time, the muscles begin to jerk and twitch for 1–2 minutes, and then the patient goes into a deep sleep.

The end of a seizure is referred to as the postictal period and signifies the recovery period for the brain. This period may last from several seconds up to a few days, though typically no more than a few hours. Postictal paresis (Todd paralysis) is a transient focal motor deficit that lasts for hours or, in rare cases, days after an epileptic convulsion. It is thought to be related either to neuronal exhaustion (from electrical overactivity during the seizure) or to active inhibition.

Diagnosis

Electroencephalography (EEG) is the most common diagnostic test for epilepsy, although a normal EEG result does not rule out the disorder. Computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT) are useful tools for revealing abnormalities in the brain that cause epilepsy. Patients with epilepsy have a higher overall mortality rate that is about twice that of the general global population. Occurrence of other associated mood disorders, particularly depression, is also higher in these patients.

Treatment

Currently available treatments help control seizure activity in 80% of patients with epilepsy. The medication used is determined by the type of epilepsy, comorbidities, age of the patient, and potential drug interactions. This latter concern specifically applies to the medication’s effect on patients who are concurrently being treated with warfarin or certain antibiotics, or who are taking oral contraceptives. For generalized tonic–clonic seizures, the first-line therapy includes valproic acid, lamotrigine, and topiramate. For partial seizures, carbamazepine, phenytoin, oxcarbazepine, or ethosuximide are often used (especially in children). To minimize side effects, monotherapy is the goal; however, use of a second agent is sometimes necessary to control breakout seizures. Adverse effects vary; they may include nausea, rash, anorexia, somnolence, dizziness, and confusion. The neurologic effects often become the dose-limiting factor. Some of these drugs used for the treatment of epilepsy can also promote hyperlipidemia, which may increase the risk of cardiovascular disease. Rare, but serious, drug reactions include Stevens-Johnson syndrome and toxic epidermal necrolysis (TEN).

When medications inadequately control seizure activity, surgery is a potential option. The most commonly performed procedure for epilepsy is removal of a seizure focus via lobectomy or lesionectomy. Other, less common surgical procedures for epilepsy include multiple subpial transections, corpus callosotomy, and hemispherectomy. An implanted vagus nerve stimulation (VNS) device can be effective in helping to control seizures in children when medication alone is not sufficient.

• Fountain NB, Van Ness PC, Swain-Eng R, Tonn S, Bever CT Jr; American Academy of Neurology Epilepsy Measure Development Panel and the American Medical Association-Convened Physician Consortium for Performance Improvement Independent Measure Development Process. Quality improvement in neurology: AAN epilepsy quality measures. Report of the Quality Measurement and Reporting Subcommittee of the American Academy of Neurology. Neurology. 2011;76(1):94–99.

• Noe KH. Seizures: diagnosis and management in the outpatient setting. Semin Neurol. 2011;31(1):54–64.

Ophthalmic considerations Transient unilateral or bilateral mydriasis can occur as an expression of seizure activity, during or after the event; it is most common in children. Horizontal or vertical gaze deviations are commonly associated with seizure activity. The gaze tends to be directed away from the side of the cortical seizure activity during the event and then toward the side of the prior activity after the seizure. Some patients experience conjugate, convergent, or monocular nystagmus during the clonic stage of a seizure. Clonic eyelid retraction has also been described in patients with absence or myoclonic seizures. It is unusual for patients with true seizures to shut their eyes during the episode, whereas patients who are feigning a seizure often keep their eyes closed.

Certain antiepileptic drugs have potential ocular side effects. Phenytoin can cause dose-related nystagmus, and maternal use of this medication is associated with fetal hydantoin syndrome, which includes hypertelorism, epicanthal folds, glaucoma, optic nerve hypoplasia, and retinal colobomas. Carbamazepine can cause blurred vision, diplopia, and nystagmus. Topiramate has been associated with acute angle-closure glaucoma, anterior chamber shallowing, acute myopia, and choroidal effusions, usually within the first 2 weeks of therapy. These effects may be an idiopathic response related to the presence of sulfa in topiramate. Treatment of the glaucoma includes cessation of the drug and use of cycloplegics and topical hypotensives.

Vigabatrin, used in refractory seizure disorders, is associated with irreversible concentric visual field loss in up to 50% of patients that is often asymptomatic. Central vision can also be affected. A complete ophthalmic examination and visual field testing should be performed before starting therapy and repeated every 3 months. The onset and progression of vision loss from vigabatrin are unpredictable and irreversible.

Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.