16
CHAPTER
Seizure Semiology
Dinesh V. Raju and Mohamad A. Mikati
Seizure semiology describes the subjective and objective signs and symptoms of a seizure. These signs are used to classify seizures (Table 16.1) and provide localizing and lateralizing information about the source of the seizures. The clinical manifestations of a seizure are thought to originate from a symptomatogenic zone. A goal of seizure semiology is to identify the area of cortical tissue from where the electrical discharge of the seizures begins. However, the symptomatogenic zone does not consistently overlap with the epileptogenic zone, the area of ictal onset (1). For example, the subjective rising abdominal feeling of medial temporal lobe epilepsy is thought to originate from the insula, but the electrical origin of the seizure can be found in the medial temporal lobe. The insula is the symptomatogenic zone, and the medial temporal lobe is the epileptogenic zone. Although the symptomatogenic and epileptogenic zones may be completely or nearly overlapping, they may be some distance part. Also, various epileptogenic zones may activate the same symptomatogenic zone, creating similar clinical seizures. The same epileptogenic zone may activate various symtomatogenic zones, generating several different types of clinical seizures (1–3).
Beyond classification, seizure semiology is an essential part of presurgical evaluation (1). It serves as a hypothesis regarding which side or specific region of the brain occupies the epileptogenic zone. Using a multimodal approach with video EEG, invasive EEG recording, imaging, neuropsychology testing, language localization, and direct electrical stimulation of cortical tissue, the epileptogenic zone may be identified in patients with the same subjective and objective signs of a seizure (1–4).
Although seizure semiology is a useful tool to classify seizures, there are limitations. There is significant variability in identifying features of seizures among trained observers. Because focal epilepsies may rapidly generalize and some generalized seizures have focal presentations, seizure semiology cannot always differentiate focal from generalized seizures. Not infrequently, inconsistent localizing and lateralizing signs may be seen during a single seizure (4).
This chapter provides a survey of the subjective and objective signs and symptoms of commonly encountered seizures and their lateralizing or localizing value.
AURAS
Auras are subjective experiences or sensations that precede a seizure that can be objectively described. Auras may last from several seconds to minutes before or may occur with variable frequency, independent of clinical seizures. Auras are thought be generated by abnormal epileptiform discharges that spread or evolve into an epileptic seizure. In certain cases, auras provide localizing information (Table 16.2).
Somatosensory Auras
Somatosensory auras are often feelings of numbness or tingling that occur in the face, arm, or leg. In some cases, these sensations can “march” from the face to the arm and to the leg, as the epileptiform discharge ascends the homunculus of the primary sensory cortex, within the postcentral gyrus. The symptomatogenic zone of somatosensory auras on one side of the face or limb is the contralateral somatosensory cortex. Auras that are experienced bilaterally, in the distal extremities or trunk, can originate from epileptiform discharges within the supplementary motor cortex. Individuals with auras originating from the supplementary motor cortex may describe sequential muscle stiffness or tightening (2,5). Direct electrical stimulation of the S2 somatosensory cortex, within the superior bank of the Sylvian fissure and the posterior insula, can cause uncomfortable sensation of heat or pain (2,5–7). Thus, somatosensory auras originate from primary somatosensory area, supplementary sensorimotor area (mesial frontal), or from the secondary sensory area (superior bank of the Sylvian fissure). Diffuse warm sensations and vague general body sensations are usually of frontal lobe origin while ictal pain is usually localized to the contralateral parietal lobe.
TABLE 16.1 Seizure Classification Based on Semiolog
Auras Somatosensory Visual Olfactory Gustatory Autonomic Abdominal Psychic |
Autonomic Seizures |
Dialeptic Seizures |
Simple Motor Seizures Myoclonic Epileptic spasms Clonic Tonic Ton–Clonic Versive |
Complex Motor Seizures Hypermotor Automotor Gelastic |
Special Seizures Atonic Akinetic Negative myoclonus Hypomotor Aphasic |
Visual Auras
Simple hallucinations of bright, colorful lights, graying of vision, and dark blotches may herald an epileptic seizure or occur after the seizure. The symptomatogenic zone of these auras is often the contralateral striate cortex (Brodmann areas 17 and 18). These hallucinations are often seen in both visual fields but can occupy a hemifield or specific quadrant, providing further localizing information. More complex visual auras with shapes and movement may originate from association cortex within the parietal and temporal lobes (2,5–8). Visual illusions are usually localized close to geniculostriate radiation and visual cortex and visual illusion of spatial interpretation to the nondominant temporal lobe.
Auditory Auras
Auditory auras can be hearing a ringing or buzzing sound. At times, there may be a nondescript noise. The symptomatogenic zone of auditory auras is Heschell’s gyrus, within the superior temporal lobe. More complex auditory auras with hearing tunes or voices are thought to originate from the temporal auditory association cortex (2,5,6,8).
Olfactory Auras
Olfactory aura is usually a nondescript smell. The symptomatogenic zones of these auras can be the amygdala or the gyrus rectus (orbitofrontal region). These auras may be a part of medial temporal lobe epilepsy (2,5).
Gustatory Auras
Gustatory auras are unpleasant, difficult to describe tastes. The symptomatogenic zones of these auras can be the insula or superior Sylvian bank. These auras may be a part of temporal or frontal lobe epilepsies (2,5).
Abdominal Auras
Abdominal auras are thought to originate from insula or superior bank of the Sylvian fissure. Abdominal auras can be various gastrointestinal complaints, such as nausea; churning or twisting of the stomach; abdominal pressure with sense of needing to pass gas; and heartburn. A common feature of this aura is a sense that the abnormal feeling rises from the abdomen into the neck or face. When the aura ascends, individuals may lose consciousness. The symptomatogenic zone of these auras includes the centromedian nucleus of the thalamus, basal ganglia, supplementary motor area, and insula. Abdominal auras can be a part of temporal or frontal lobe epilepsies (2,5).
TABLE 16.2 Localization and Lateralization of Auras
TYPE OF AURA | LOCALIZATION | LATERALIZATION |
Unilateral Somatosensory | Somatosensory cortex | Contralateral |
Bilateral somatosensory | Supplementary motor cortex |
|
Static visual hallucinations | Striate cortex | Contralateral |
Complex visual hallucinations | Extrastriate cortex |
|
Simple auditory | Heschell’s gyrus |
|
Complex auditory | Temporal association cortex |
|
Olfactory | Amygdala, gyrus rectus |
|
Gustatory | Insula |
|
Abdominal | Centromedian nucleus of the thalamus, basal ganglia, supplementary motor area, insula |
|
Autonomic | Insula, anterior cingulate gyrus |
|
Psychic | Temporal association cortex |
|
Autonomic Auras
Autonomic auras can present as sweating, palpitation, yawning, and changes in breathing. During autonomic seizures, heart rate and respiratory rate may be measured and show abnormal rates or patterns. Unlike seizures, autonomic auras are subjective sensations that are not measured. The symptomatogenic zone of these auras can be the insula basal frontal and anterior cingulate gyrus (2,5,8). Ictal piloerection is usually ipsilateral to the seizure focus.
Psychic Auras
Psychic auras are a misperception of the self or the outside world. Examples of psychic auras include fear, anxiety, extreme joy, deja vu, jamais vu, and autoscopy. Deja vu is a sense that a particular situation or experience occurred before, whereas jamais vu is a sense that the situation or experience is foreign. Autoscopy is a distortion of one’s self. Individuals feel an “out of body” experience and describe a feeling of being disconnected from but being able to observe their body from a distance. In some cases, individuals are unable to perceive his/her body. The symptomatogenic zone is often temporal association cortex and limbic cortex. These auras can occur in temporal lobe epilepsies (2,5,8).
SIMPLE MOTOR SEIZURES
Simple motor seizures are characterized by unnatural movements of one limb or the whole body in one plane (Table 16.3). These seizures can be further classified based on the muscle groups involved, and duration and rhythm of movement. Often, electrical stimulation of the primary motor cortex or supplementary motor cortex can produce simple motor seizures (2,6,8).
Myoclonic Seizures
Myoclonic seizures are characterized as sudden, usually nonrhythmic, jerks lasting usually less than 400 ms per jerk. These “lightening”-like jerks may occur in one limb or be generalized. Electrical stimulation of the primary motor cortex or premotor cortex can create these seizures. Myoclonic seizures occur in generalized seizures (2,6,8).
Clonic Seizures
Clonic seizures involve semi-rhythmic to rhythmic contraction of muscles, alternating with periods of reduced muscle tone or contraction. These seizures may begin with a tonic contraction of the muscle(s) and then become clonic. Clonic seizure may be focal, involving distal extremities, such as the hand or foot. Focal clonic seizures of the face may present as pulling of one side of the faces. These seizure may spread or “march” from the distal extremity to more proximal regions, including the face (2,6,8).
Clonic seizures may be unilateral or generalized. The primary motor cortex and premotor cortex can generate these seizures. Electrical stimulation of the supplementary motor cortex can create clonic seizures of distal extremities. Frontal lobe epilepsies may include clonic seizures. In temporal lobe epilepsies, clonic seizures often involve the frontal eye fields, face, and hands, more so than the legs. In secondarily generalized seizures, clonic contractions contralateral to the seizure onset may reduce or stop before contraction ipsilateral to the ictal focus (2,5,6,8).
Tonic Seizures
Tonic seizures commonly exhibit as persistent muscle contraction of the proximal extremities. Although both sides of the body may be involved, there is usually an asymmetry, causing an unnatural posture or positioning of the body. These muscle contractions usually last more than 3 seconds per contraction. The appearance of the seizure can vary, depending on the symptomatogenic zone (2,6,8).
