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Seizures are among the most common problems in neurology. Up to 10% of the population will have a seizure at some point in their lives. In addition, seizures can be among the most dramatic forms of nervous system dysfunction. Although seizures have many different causes and manifestations, by definition a seizure is an abnormal hypersynchronous electrical discharge of neurons in the brain, producing a clinical dysfunction. Epilepsy is defined as a condition in which there is a tendency to have recurrent unprovoked seizures. Practically, the diagnosis of epilepsy is often applied after a patient has had two unprovoked seizures.
CLASSIFICATION
Seizures can arise from one specific focus within the brain (focal) or involve both cerebral hemispheres at the onset (generalized). The diagnosis and categorization of the seizure is based primarily on the semiology (i.e., signs or symptoms) characterizing the event. Those that arise from one portion of the brain can evolve and spread to involve the whole brain (secondarily generalized). Among focal seizures, those in which awareness is impaired are termed “with impaired awareness” (previously “complex”), whereas those in which awareness is preserved are termed “aware” (previously “simple”) (Table 15-1).
FOCAL SEIZURES
By definition, focal seizures (previously termed “partial”) begin in a focal area of the brain and do not impair awareness, at least at the onset (Fig. 15-1A). In general, such seizures lead to positive rather than negative neurologic symptoms (e.g., tingling rather than numbness; hallucinations rather than blindness). The manifestations of focal seizures depend on their site of origin in the brain. These are designated as motor or nonmotor. Focal motor seizures, in which one part of the body may stiffen or jerk rhythmically, involve the motor cortex in the frontal lobe. The classic Jacksonian march occurs when the electrical discharge spreads along the motor strip, leading to rhythmic jerking that spreads along body parts following the organization of the motor homunculus. Focal nonmotor seizures from other regions of the brain can cause sensory phenomena (sometimes parietal), visual phenomena (usually occipital), or gustatory, olfactory, and psychic phenomena (frequently temporal). The latter may include déjà vu, jamais vu, or sensations of depersonalization (“out of body”) or derealization.
TABLE 15-1. Types of Seizures | |
Focal-onset: | |
Motor | Myoclonic (jerking) Epilepsia partialis continua (sustained rhythmic jerking) Clonic (rhythmic movements) Tonic (stiffening) Hypermotor (e.g., running) Focal-onset with secondary generalization (generalized convulsion) |
Non-motor | Focal-onset with impaired awareness (old “complex partial’) Sensory, e.g., olfactory, somatosensory, or hemianopic Focal-onset with altered cognition, e.g., aphasic, amnestic, ‘psychic’ / ‘emotional’ (e.g., altered mood, rage) Autonomic |
Generalized–onset: | |
Motor | Generalized, tonic (then) clonic, convulsion (‘grand mal’) Myoclonic Tonic Atonic (lack of tone, with falls) |
Non-motor: | Absence Other primary absence-like seizures, eyelid myoclonia Myoclonic–absence Generalized nonconvulsive seizures in comatose or ICU patients Autonomic |
FIGURE 15-1. Characteristics of seizure types. (A) Focal-onset seizures. (B) Generalized seizures. (Reprinted with permission from Ford SM. Roach’s Introductory Clinical Pharmacology. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2017. Figure 29.1.)
FOCAL SEIZURE WITH IMPAIRED AWARENESS
Focal seizures with impaired awareness (previously termed complex partial seizures) have a focal onset and involve an impairment of awareness. Many arise in the temporal lobe, but a frontal lobe focus is also common. Focal seizures with impaired awareness may include automatisms (stereotyped motor actions without clear purpose) such as lip-smacking, chewing movements, or picking at clothing. The patient may have speech arrest or may speak in a nonsensical manner. By definition, the patient does not respond normally to the environment or to questions or commands. Occasionally, patients may continue the activities they were participating in at the onset of the seizure, sometimes to remarkable lengths: Patients may continue folding laundry during a seizure or even finish driving home. Focal seizures with impaired awareness of frontal lobe origin may involve strange bilateral movements, such as bicycling or kicking, or behavior such as running in circles. If the patient’s awareness is not known, the seizure is termed a focal seizure with unknown awareness.
GENERALIZED SEIZURES
Generalized seizures include two categories: motor seizures and absence seizures (Fig. 15-1B).
GENERALIZED MOTOR SEIZURES
Generalized motor seizures were previously referred to as generalized tonic–clonic (GTC) seizures or grand mal seizures. This is the seizure type with which the lay public is most familiar. They typically begin with a tonic phase, lasting several seconds, in which the entire body becomes stiff (including the chest and pharyngeal muscles, sometimes leading to a vocalization known as the epileptic cry). This is followed by the clonic phase, in which the limbs jerk rhythmically, more or less symmetrically, typically for less than 1 to 2 minutes. Toward the end of the clonic phase, the frequency of the jerking may decrease and stop as the body becomes flaccid. The patient may bite the tongue and become incontinent of urine during a generalized motor seizure. There is typically a postictal state after the seizure, lasting minutes to hours, during which the patient may be tired or confused, before returning to normal activity slowly.
FIGURE 15-2. Characteristic EEG findings in absence seizures. (A) Normal EEG recording in an awake adult. The top four channels are derived from electrodes over the left side of the head, from front to back; the bottom four are derived from the right side of the head. A normal sinusoidal alpha rhythm is seen most prominently over the posterior head regions bilaterally (fourth and eighth channels). (B) Midway through the recording, rhythmic 3-Hz generalized spike-and-slow-wave discharges appear. This is the typical EEG pattern of an absence seizure. During these discharges, the patient may stare and be unresponsive. (From Ginsberg L. Lecture Notes: Neurology. 8th ed. Oxford: Blackwell Publishing; 2005:75. Copyright © 2005 L Ginsberg. Reprinted by permission of John Wiley & Sons, Inc.)
ABSENCE SEIZURES
An absence seizure is a generalized seizure that most commonly occurs in children or adolescents and is characterized primarily by an unresponsive period, often with staring, that lasts for several seconds, with immediate recovery thereafter. Absence seizures can occur tens or even hundreds of times a day and may be noticed first by schoolteachers and assumed to be daydreaming or difficulty concentrating. A classic 3-per-second generalized spike-and-wave electroencephalogram (EEG) pattern accompanies absence seizures (Fig. 15-2). Hyperventilation is a common trigger.
OTHER GENERALIZED SEIZURE TYPES
Less common seizure types include myoclonic–atonic, clonic–tonic–clonic, myoclonic absence, and absence with eyelid myoclonia, all of which are generalized in onset (Table 15-1). Seizures that are myoclonic (without other features) may be generalized or focal.
UNKNOWN ONSET
Unknown onset is the last seizure classification and is used when the semiology and onset of the seizure are unknown. This term should be used when the onset of the seizure was not witnessed or the description is unclear. Any information about the seizure semiology that is known should be added to the diagnosis, such as motor or nonmotor as well as the description of awareness during the seizure.
UNCLASSIFIED
If no information is known about the seizure semiology, the seizure is labeled as unclassified. This is a term that should be reserved for patients for whom no additional information is available. This term should be revised when additional clinical information about the seizure semiology becomes available.
KEY POINTS
●A seizure is an abnormal hypersynchronous electrical discharge involving neurons in the brain, with a clinical correlate.
●Epilepsy is a tendency to have recurrent unprovoked seizures.
●Focal seizures may manifest with motor, sensory, or psychic phenomena and are usually characterized by positive rather than negative neurologic symptoms.
●Focal seizures originate in a focal area of the brain but may become bilateral tonic–clonic seizures; awareness is preserved during the focal seizures but becomes impaired during secondary generalization.
●Generalized seizures originate in the entire brain at once; tonic–clonic and absence seizures are examples.
EPIDEMIOLOGY AND ETIOLOGIES
Seizures have a U-shaped distribution in age of onset—they are more common in the very young and the very old. Etiologies vary depending on the age of onset. In infants, a variety of neonatal infections, hypoxic-ischemic insults, genetic syndromes, and congenital brain malformations are common causes of seizures.
Febrile seizures are a special case. They are the most common cause of seizures in children, affecting up to 3% to 9% of this age group. They occur between 6 months and 5 years of age in the setting of a febrile illness without evidence of intracranial infection and are usually generalized in onset. Most children with febrile seizures do not have neurologic deficits. For the event to be considered a febrile seizure, the fever may be present before the seizure or must develop in the immediate postictal period. The risk of subsequent epilepsy is relatively small unless the seizures are prolonged or focal in onset or if other neurologic abnormalities or a family history of epilepsy is present.
Older children may also develop seizures related to head injury, meningitis, encephalitis, or vascular diseases, and genetic syndromes continue to be a significant etiology in this age group. Among young adults, head injury, substance use, and excessive alcohol use are common causes of new-onset seizures, but brain tumors and strokes become more common etiologies by middle age. In the elderly, strokes become the most common etiology, but substance abuse and alcohol are not uncommon causes. Metabolic disturbances from systemic problems such as severe hypo- or hyperglycemia, hepatic failure, or renal failure are also frequent causes.
KEY POINTS
●The incidence of new-onset seizures has a U-shaped distribution, highest among the very young and the very old.
●Common etiologies of new-onset seizures differ depending on the age of onset.
●Febrile seizures in children are common and generally carry a benign prognosis.
●Seizures may occur as part of specific epilepsy syndromes characterized by distinctive seizure types, EEG patterns, or associated neurologic abnormalities.
Frequently, seizures occur in children (and sometimes adults) as part of a syndrome that may include specific seizure types, EEG patterns, and associated neurologic abnormalities. Many of these are called “idiopathic generalized epilepsies”—usually considered to be genetic conditions in almost all cases. The diagnosis of a specific syndrome may have implications both for genetic testing and for the proper choice of pharmacologic treatments. Examples of epilepsy syndromes are outlined in Table 15-2.
TABLE 15-2. Epilepsy Syndromes: Features and Treatment | |||||
Selected Epilepsy Syndromes | |||||
Age of Onset | Seizure Types | Associated Findings | EEG Findings | Commonly Used Treatments | |
Lennox–Gastaut syndrome | Childhood | Tonic, atonic, myoclonic, generalized tonic–clonic, absence | Major cognitive impairment and disability | Slow (1- to 2-per-second) spike-and-wave discharges | Valproic acid, lamotrigine, felbamate, rufinamide, clobazam |
Focal motor seizure, e.g., benign rolandic epilepsy | Childhood | Simple partial seizure involving the mouth and face, infrequent generalized tonic–clonic | Nocturnal preponderance of seizures | Centrotemporal spikes | Carbamazepine; sometimes no treatment necessary |
Absence epilepsy | Childhood and adolescence | Absence; sometimes, generalized tonic–clonic seizures | Hyperventilation as trigger | 3-per-second generalized spike-and-wave | Ethosuximide, valproic acid, lamotrigine |
Juvenile myoclonic epilepsy | Adolescence and young adulthood | Myoclonic, absence, generalized tonic–clonic | Early morning preponderance of seizures | 4- to 6-per-second polyspike-and-wave | Valproic acid, lamotrigine, levetiracetam |
EEG, electroencephalogram. | |||||
CLINICAL MANIFESTATIONS
HISTORY
The diagnosis of seizures is a clinical one. Most commonly the patient is seen after an event has occurred, and the diagnosis must be made on the history alone. In these cases, the patient (and more importantly, witnesses, if the seizure was generalized in onset) must be questioned for an exact description of the event itself (and especially the onset), any premonitory symptoms, and the character of the recovery period in order for the clinician to decide whether the event was a seizure, and, if so, what type of seizure it was. The clinical details should allow for the differentiation of seizures from other paroxysmal neurologic events (Table 15-3).
PHYSICAL EXAMINATION
The neurologic examination is most helpful diagnostically in the (relatively uncommon) instances in which the patient is observed during the event or shortly thereafter. In the latter case, a postictal hemiparesis, or Todd’s paralysis, may be detected after a bilateral tonic, then clonic seizure; this suggests that the seizure was of focal onset, even if not apparent to observers at the time. Other abnormalities on neurologic exam may also suggest the presence of a focal brain lesion. Of course, the general physical exam may yield findings suggestive of infection or other systemic disease that might explain a new-onset seizure. In particular, signs of meningitis should be sought in any patient who has had a seizure.
TABLE 15-3. Characteristics of Focal Seizures and Other Paroxysmal Neurologic Events | |||
Focal Seizures | Transient Ischemic Attacks | Migraine | |
Onset | Progression of symptoms over seconds | Sudden onset of symptoms | Progression of symptoms over 15–20 min |
Neurologic symptoms | Positive motor or sensory symptoms; “psychic” symptoms such as déjà vu | Negative motor, sensory, or visual symptoms (loss of function) | Positive sensory and, especially, visual symptoms such as scintillating scotomata |
Duration | Usually less than a few minutes | Usually less than 30 min, always less than 24 h | Symptoms for 15–20 min, typically followed by headache for hours |
Consciousness | Preserved or impaired | Preserved | Preserved |
Headache | Occasionally postictal | Infrequent | Throbbing pain, often unilateral, following the progression of initial symptoms |
Recovery | Postictal confusion, sleepiness | Rapid | Fatigue common |
Risk factors | Structural brain lesion, family history of seizures | Hypertension, hyperlipidemia, smoking, diabetes, atrial fibrillation, stenotic intracranial or extracranial vessels, hypercoagulability | Family history of migraines |
DIAGNOSTIC EVALUATION
LABORATORY STUDIES
Laboratory testing may show an underlying metabolic abnormality, such as hyponatremia or hypocalcemia, that explains a new-onset seizure. After a generalized seizure, there is commonly a lactic acidosis, resulting in decreased serum bicarbonate. A toxicology screen for common substances of abuse, as well as an alcohol level, should be done in all patients. Female patients of reproductive age should also have a pregnancy test. In cases where infection is suspected, a lumbar puncture should be performed.
BRAIN IMAGING
An uncomplicated seizure in a patient with known epilepsy does not generally warrant brain imaging. With rare exceptions, however, neuroimaging should be performed in patients with new-onset seizures. For seizures of probable focal onset, a magnetic resonance imaging (MRI) is a necessary part of the diagnostic workup, to look for a structural abnormality that is a focus for that seizure. A head computed tomography may suffice in the urgent setting.
KEY POINTS
●Most neurologists begin drug therapy after two unprovoked seizures.
●Each drug has its own set of indications and adverse effects.
●Monotherapy is a desired goal of antiseizure therapy; most patients’ seizures are well controlled on one medication.
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