Simple Partial Seizures

Simple partial seizures are seizures in which consciousness is not altered at any point throughout the course of the seizure. The 1981 ILAE classification divides them into four major categories:

Although most simple partial seizures would be classified in one of these categories, it is quite possible for a simple partial seizure to have manifestations that belong in more than one category. For example, simple partial seizures may start with a sensory experience which then evolves into motor activity. Simple partial seizures of purely subjective nature are often referred to as auras or isolated auras. The manifestations of simple partial seizures depend on the brain region involved in the ictal discharge. However, it is important to recognize that for simple partial seizures as well as other partial-onset seizures, the seizure activity may originate in silent areas, and the first clinical manifestations may reflect seizure spread to other brain regions. Nevertheless, simple partial seizures and auras may have important lateralizing and localizing value. For example, focal clonic or tonic activity is usually contralateral to the hemisphere involved in seizure activity. Somatosensory auras, visual auras, and auditory auras are often useful in suggesting localization and lateralization of the epileptogenic zone. However, some auras are non-specific and may be seen with a variety of localizations.

Auras are typically short in duration, lasting seconds to minutes. Some patients may experience a prodrome, a difficult-to-describe feeling that a seizure may occur. Prodromes may last hours or even days and have to be distinguished from auras. On the other hand, auras may occasionally be prolonged, in which case they are called aura continua, which is a form of simple partial status epilepticus.

The most recent recommendation of the ILAE Commission on Classification and Terminology suggested eliminating the term simple partial. Instead, it recommended descriptors of focal seizures according to degree of impairment during a seizure. Seizures without impairment of consciousness or awareness are divided into those with observable motor or autonomic components and those only involving subjective sensory or psychic phenomena (Berg et al., 2010).

Complex Partial Seizures

Complex partial seizures are characterized by altered consciousness during the seizure. Impairment may be very subtle, manifesting with slight confusion, fuzziness, or slowing of responses. A patient may have some recollection of events or total amnesia for the event. Complex partial seizures may have a simple partial onset. It is sometimes difficult to determine if consciousness was impaired. The patient may be totally conscious but unable to respond verbally because of aphasia or unable to respond or react because of motor inhibition. When the simple partial onset is purely subjective, it is commonly referred to as an aura.

Complex partial seizures may arise from any lobe but most commonly arise from the temporal lobe; the frontal lobe is the second most common site of seizure origin. Complex partial seizures may include motor activity. The most common type of motor activity in this seizure type is automatism, described earlier. The different complex partial seizure patterns in seizures arising from different lobes of the brain will be discussed in the next section.

Partial Seizures Evolving to Generalized Tonic-Clonic Activity

These seizures may start as simple partial, complex partial, or simple partial evolving to complex partial. The transition to secondary generalization usually involves versive head turning in a direction contralateral to the hemisphere of seizure onset, and focal or lateralized tonic or clonic motor activity. The pattern of evolution may be clonic-tonic-clonic in some instances. The generalized tonic phase may be asymmetrical, with flexion on one side and extension on the other. This has been called figure-of-4 posturing (Kotagal et al., 2000). Some asymmetry and asynchrony may also occur in the clonic phase, resulting in a slight degree of side-to-side head jerking (Niaz et al., 1999). The evolution from tonic to clonic activity is gradual and not always simultaneous in all affected body parts. A phase of high-frequency tremor has been referred to as the tremulous or vibratory phase of the seizure (Theodore et al., 1994). Clonic activity typically decreases in frequency over time, with longer intervals between jerks towards the termination of the seizure. The clonic activity may end on one side of the body first, so that clonic activity may then appear lateralized to one side. In addition, there may be a late head turn ipsilateral to the hemisphere or seizure origin (Wyllie et al., 1986). After the motor activity stops, the individual is usually limp and has a loud snoring respiration often referred to as stertorous respiration. During the course of recovery, there may be variable agitation. The speed of recovery is expected to be slower with longer and more severe seizures.

Partial Seizure Semiology in Relation to Localization

Generalized Absence Seizures

Typical absence seizures are characterized by a sudden blank stare with motor arrest, usually lasting less than 15 seconds (Commission on Classification and Terminology of the International League Against Epilepsy, 1981). The individual is usually unresponsive and unaware. The seizure ends as abruptly as it starts, and the patient returns immediately to a baseline level of function with no postictal confusion but may have missed conversation and seems confused as a result. If the only manifestation is altered responsiveness and awareness, with no associated motor component, the absence seizure is classified as simple absence. Most often, generalized absence seizures include mild motor components and are classified as complex absence. The most common motor components are automatisms such as licking the lips or playing with an object that was held in the hand before the seizure. Other motor components include clonic, tonic, atonic, and autonomic manifestations. Clonic activity may affect the eyelids or the mouth. An atonic component may manifest with dropping an object or slight head drop or drooping of the shoulders or trunk. Tonic components may manifest with slight increase in tone.

The EEG hallmark of a typical generalized absence seizure is generalized 2.5- to 4-Hz spike-and-wave activity with a normal interictal background (Fig. 67.1). Atypical absence seizures are diagnosed primarily based on a slower (<2.5 Hz) frequency of the EEG spike-and-wave activity. Less important distinctions are that the onset and termination of an atypical absence seizure may be less abrupt and the motor components a bit more pronounced than seen with typical absence seizures. Atypical absence seizures usually occur in individuals with impaired cognitive function. Affected individuals usually have associated seizure types such as generalized tonic, generalized atonic, and generalized tonic-clonic seizures.

Fig. 67.1 Generalized absence seizure displayed with referential montage using linked ear reference. Spike-and-wave discharges are bifrontally predominant.

Additional generalized absence seizure types recently recognized by the ILAE include myoclonic absences. The key manifestation of these seizures is a prominent rhythmic myoclonus predominantly affecting the limbs (Bureau and Tassinari, 2005b). Otherwise, myoclonic absences resemble typical absence seizures with respect to impairment of consciousness, although this impairment can be only partial. Another related seizure type recently recognized is eyelid myoclonia with absence. The eyelid myoclonia consists of pronounced rhythmic jerking of the eyelids, usually associated with an upward deviation of the eyes and retropulsion of the head (Caraballo et al., 2009). There may or may not be associated generalized spike-and-wave activity on EEG. Absence seizures may evolve to generalized tonic-clonic activity (Mayville et al., 2000).

Generalized Myoclonic Seizures

Myoclonic seizures are muscle contractions lasting a fraction of a second (<250 msec), in association with an ictal EEG discharge (Blume et al., 2001). The myoclonic jerk can be generalized, affecting the whole body, or could affect just the upper extremities or (rarely) the head or trunk, or even the diaphragm. The myoclonic jerks may affect one side of the body at one time, but typically the other side is affected at other times. The jerks can be single or could occur in an arrhythmic cluster. It should be noted that myoclonus is not always epileptic (Faught, 2003). Myoclonus can be generated anywhere along the central nervous system (CNS). Epileptic myoclonus is generated in the cerebral cortex and is usually associated with a single or brief serial spike-and-wave or polyspike-and-wave activity.

Negative myoclonic seizures consist of a very brief pause in muscle activity rather than a brief muscle contraction (Rubboli and Tassinari, 2006). Just as with positive myoclonus, negative myoclonus can be generalized, bilateral with limited distribution, or even focal, typically with shifting lateralization.

Myoclonic seizures may be immediately followed by a loss of tone. The seizure type is called myoclonic-atonic. Historically it was called myoclonic-astatic. The seizures are brief (1 second or less) but may be associated with falls and injuries. The EEG shows generalized spike-and-wave or polyspike-and-wave discharge. The slow wave is prolonged and associated with the electromyographic (EMG) silence characteristic of the atonic phase. Myoclonic seizures may precede a more sustained tonic contraction, and the resultant seizures may be referred to as myoclonic-tonic seizures (Berg et al., 2010). Generalized myoclonic seizures may cluster just before a generalized tonic-clonic seizure occurrence.

Generalized Clonic Seizures

Unlike myoclonic seizures, which are single jerks (but may occur in arrhythmic clusters), each generalized clonic seizure consists of a series of rhythmic jerks. Generalized clonic seizures are uncommon and particularly rare in adults (Noachtar and Arnold, 2000). They are more frequently seen in certain epileptic syndromes of infancy and childhood. For example, clonic seizures are a common seizure type of severe myoclonic epilepsy of infancy (Dravet syndrome). Clonic seizures are also noted in progressive myoclonic epilepsies.

Generalized Tonic Seizures

Generalized tonic seizures are typically brief seizures, a few seconds to 1 minute. Their onset may be gradual or abrupt. They may be initiated with a myoclonic jerk. They can vary in severity from subtle, with slight increase in neck tone with upward deviation of the eyes, to massive, with involvement of the axial muscles and extremities. Proximal muscles are the most affected. Most commonly there is neck and trunk flexion as well as abduction of the shoulders and flexion of the hips. However extension may also occur. Tonic seizures may be asymmetrical, which could result in turning to one side. The pattern of muscle involvement may change over time so that there may be a change in the position of the limbs over the course of the seizure. Autonomic changes may occur, with tachycardia, pupil dilation, and flushing. Involvement of respiratory muscles could cause apnea and cyanosis. The tonic contraction may end with one or more pauses that result in a few clonic jerks. A postictal state with confusion may occur, but recovery is usually rapid. However, tonic seizures may be followed by atypical absence, resulting in what appears to be a more prolonged postictal state. This has been referred to as tonic-absence seizure (Shih and Hirsch, 2003). Generalized tonic seizures occur most often out of sleep and drowsiness.

Epileptic Spasms

Epileptic spasms have similarities to generalized tonic seizures but a shorter duration that is intermediate between generalized myoclonic and generalized tonic seizures (Blume et al., 2001), with a typical duration of 0.5 to 2 seconds. The pattern of contraction is “diamond-shaped,” with intensity of contraction maximal in the middle of the spasm and less at the beginning and end. Epileptic spasms are also called infantile spasms and salaam attacks. Because their occurrence is not restricted to infants, the preferred current term is epileptic spasms. The classic epileptic spasm involves neck and trunk flexion and arm abduction with a jackknife pattern, but extension may be seen. Epileptic spasms typically occur in clusters recurring every 5 to 40 seconds. In a cluster, the initial spasms may be subtle or mild, increase in intensity as the cluster progresses, and decrease in intensity again toward the end of the cluster (Bleasel and Lüders, 2000).

Generalized Tonic-Clonic Seizures

Generalized tonic-clonic (GTC) seizures are dramatic and the best recognized form of seizures. They are commonly referred to as grand mal, but this term is archaic and does not distinguish seizures of focal onset from those with a generalized onset. Generalized tonic-clonic seizures do not have an aura, but they may be preceded by a prodrome—the vague sense a seizure will occur—lasting up to hours. Seizure onset is abrupt, most often with loss of consciousness and a generalized tonic contraction, but some seizures may be initiated with a series of myoclonic jerks, leading to the term clonic-tonic-clonic seizure. The tonic phase may have asymmetrical movements, and these often change from seizure to seizure. One such commonly encountered asymmetry is versive head turning, which is not evidence of a focal onset (Chin and Miller, 2004; Niaz et al., 1999). The tonic phase includes an upward eye deviation with eyes half open and the mouth open. Involvement of the respiratory muscles usually produces a forced expiration that produces a loud guttural vocalization, often referred to as the epileptic cry. Cyanosis may occur during the tonic phase in association with apnea. The tonic phase gradually evolves to clonic activity. The transition can be with initially high-frequency and low-amplitude motion, often referred to as a vibratory phase. With seizure progression, the frequency of clonic jerks decreases, and the amplitude may initially increase but later decreases just before the seizure stops. In the immediate postictal state the individual is limp and unresponsive. Respiration is loud and snoring in character (stertorous). The postictal state is often followed by sleep, although the individual may awaken briefly with postictal confusion. Tongue biting commonly occurs and most often affects the side of the tongue. Incontinence of urine is common, and incontinence of stool may also occur. After awakening, patients often have a pronounced headache and generalized muscle soreness. Generalized tonic-clonic seizures rarely last more than 2 minutes. The severity may vary. The postictal state seems to correlate with severity and duration.

Generalized Atonic Seizures

Generalized atonic are associated with very brief, sudden loss of tone and vary from extremely subtle, manifesting with only a head drop, to generalized loss of tone and falling. Atonic seizures may result in falling if the person is standing, then called a drop attack. However, drop attacks may be the result of both generalized atonic and generalized tonic seizures. There is a very brief loss of consciousness and brief postictal confusion. Seizures are usually very brief, lasting 1 second to a few seconds. They may be preceded by a brief myoclonic jerk, in which case the seizure type is called myoclonic-atonic. Very brief atonic seizures are typical of the syndrome of myoclonic-astatic epilepsy (Doose syndrome) (Oguni et al., 2001). More prolonged atonic seizures can be seen with Lennox-Gastaut syndrome or other symptomatic generalized epilepsies. Despite their brief duration, generalized atonic seizures can result in serious injury and are an important cause of morbidity in epilepsy.

Generalized-Onset Seizures with Focal Evolution

Generalized-onset seizures rarely may evolve to focal seizures (Deng et al., 2007; Williamson et al., 2009). This seems to occur with either myoclonic or absence seizures. The clinical manifestations most often are behavioral arrest and staring, with minor automatisms. However, focal motor manifestations may also occur. This type of seizure tends to be prolonged and may be associated with postictal confusion (Williamson et al., 2009).