Generalized tonic-clonic seizures typically have no preceding aura but may have a prodrome of apathy or irritability. They may occur either as a generalized seizure type, with no aura or focal onset, or as a “focal to bilateral tonic-clonic seizure” (formerly known as secondary generalization) from a focal-onset seizure. During the tonic phase, the jaw snaps shut followed by 10-15 seconds or longer of tonic spasms, apnea, and cyanosis. The arms stiffen in extension at the elbow with flexion at the wrists and are held forward and adducted, and knees are locked in extension with plantar flexion at the ankles. A fine tremor is sometimes superimposed. The clonic phase usually consists of 1-2 minutes of rhythmic generalized muscle contractions, synchronously involving both sides of the body, with increased blood pressure, excessive salivation, and decreased respiration. The postictal phase lasts for minutes to hours with confusion, somnolence, headache, and possibly agitation, undirected aggression, or fear. Urinary and/or fecal incontinence may occur early in the postictal period. The EEG may show generalized spike-and-wave, generalized rhythmic fast activity, or other patterns but is often obscured by muscle and movement artifact during the convulsive phase.

Generalized seizures are rare in newborns. In children, generalized seizures occur most frequently secondary to fevers and metabolic derangements.

Absence seizures typically have no preceding aura or prodrome. An absence seizure usually lasts for only several seconds to minutes. There is a sudden interruption of consciousness, staring, blinking (sometimes at 3 Hz), and rarely automatisms. There is no postictal confusion. The EEG in absence shows 3-Hz generalized spike-and-wave,
often with bifrontal but sometimes bioccipital emphasis. Discharges may begin slightly faster (up to 4 Hz) and may slow to <3 Hz by the end of the seizure. The background activity quickly returns to normal when the seizure is over.

The seizures associated with juvenile myoclonic epilepsy typically have no preceding aura but may have a prodrome of repetitive myoclonus, most often occurring in the morning. The seizures usually consist of generalized tonic-clonic activity; however, absence seizures may also occur. Atypical characteristics such as asymmetric myoclonus or versive (forced turning) movements are not uncommon.⁵ The postictal phase is variable depending on the seizure type.

The age of onset of juvenile myoclonic epilepsy is typically 10-20 years. Patients are usually developmentally and neurologically normal. The EEG usually shows a normal background with interictal bursts of 5- to 6-Hz generalized spike-and-wave or polyspike-and-wave discharges. A photoparoxysmal response to photic stimulation can occur.

The family of disorders known as the progressive myoclonic epilepsies (Table 14.1) consists of a number of loosely related disorders. These epilepsy subtypes are quite rare and have complex presentations and diagnostic findings. Most of these disorders have a genetic basis, though sporadic cases have occurred. The EEG associated with these disorders is variable. The background is often slow. The seizures are typically generalized. These disorders are considered in more detail in Chapter 12.

Tonic seizures are a generalized seizure type with sudden axial stiffening and extension of the outstretched arms at the shoulder in an upward direction reminiscent of the football “touchdown” sign. They may last only a few seconds with no loss of awareness, though longer tonic seizures lasting 30 seconds or longer are suggestive of the tonic phase of generalized tonic-clonic seizures. Brief tonic seizures often occur in clusters. The EEG findings may be subtle and obscured by the sudden movement but classically show generalized paroxysmal fast activity (GPFA), which appears as a low-amplitude fast beta activity, sometimes superimposed on a high-amplitude slow delta transient that may be due to a DC shift or movement artifact.

Atonic seizures can be considered the opposite of tonic seizures. There is sudden loss of axial tone, usually beginning at the neck with a head drop followed by bending forward at the waist and loss of tone in the legs resulting in a fall, usually with loss of consciousness. Head injuries including skull fractures are common, and a helmet should be prescribed if seizures are not controlled. The ictal EEG usually consists of a generalized polyspike-and-wave pattern, with the fall occurring during the slow-wave component. Both tonic and atonic seizures are usually seen in the context of the Lennox-Gastaut syndrome, defined as the triad of multiple seizure types, slow (<3 Hz) spike-and-wave, and mental retardation.

Epileptic spasms are most often seen in the context of West syndrome, which typically begins between 3 months and 3 years of age. The term “infantile spasms” continues to be used, but newer terminology emphasizes that these seizures are not limited to infancy. The seizures associated with West syndrome consist of a jackknifing movement at the waist and myoclonus. The EEG consists of a high-voltage, chaotic pattern known as hypsarrhythmia with bursts of asynchronous slow waves, spikes and sharp waves that alternate with a suppressed EEG. The clinical features of West syndrome include epileptic spasms and arrest of cognitive development with subsequent mental retardation, which varies according to the etiology of the spasms.⁶

Aicardi syndrome is an X-linked disorder present from birth, which is associated with epileptic spasms.⁶ Alternating hemiconvulsions may also be seen. The clinical features of Aicardi syndrome include coloboma (an iris defect due to incomplete closure of the optic cup), chorioretinal lacunae, agenesis of the corpus callosum, vertebral anomalies, and seizures. See Chapter 12 for further details.