The typical LGS seizures (i.e., tonic, atonic, atypical absence and myoclonic) usually begin at age 3 years, typically between age 1 and 7 years. Most patients with LGS have daily seizures. Video-EEG monitoring may help correctly classify each seizure type. This classification has implications for treatment and may improve the selection of therapy. Below I will describe each of the seizure types.

Tonic Seizures

Tonic Seizures are the most common and most characteristic type, and form the core of the syndrome. Tonic seizures consist of a sustained increase in muscle contraction lasting a few seconds to minutes (resulting in stiff extremities). These may be limited to a slight bent of the body at the neck and waist with a brief interruption of breathing or may be characterized by stronger seizures with facial grimacing and stiffening and slow elevation of the arms. Tonic seizures occurring in wake may result in a fall (simulating a drop attack), but are more common in sleep. Tonic seizures may not be present at the onset of LGS, or may be missed if a sleep EEG is not obtained. Some events in sleep may be subtle, with only a slow movement of the eyes upward and tensing of the muscles of the chest or abdomen (associated with a specific EEG change). If they occur only during sleep they may go unnoticed. The presence of tonic seizures is associated with a poor prognosis for development. Repetitive tonic seizures, admixed with atypical absence seizures, resulting in non-convulsive status epilepticus are not uncommon. Tonic seizures last from a few seconds to a minute, and if longer they can have a tremor or vibratory component.

Atypical Absences

Atypical absence seizures are the second most common seizure type associated with LGS. This seizure is represented by a brief loss or lapse of awareness (usually seconds, 15-30). This makes this seizure difficult to identify because of its gradual onset and ending in a child whose developmental delay may already limit their responsiveness. Typically, the child can not tell the parent they are experiencing an interruption in their awareness, and the parent may believe they are inattentive, daydreaming or simply still for the moment. The EEG shows a characteristic slow-spike and wave pattern during these events.

Complex partial seizures my also occur in LGS and present with staring episodes, resulting in confusion with atypical absence seizures. A video-EEG to capture a typical event may be necessary to tell if the staring episode is indeed a seizure, and, if so, what type, as this has important implications for treatment.

Atonic Seizures or Drop Attacks

Drop attacks occur in slightly over half of patients with LGS. These seizures result in repeated falls, with subsequent injury to the face and head. These injurious seizures should be the primary factor to consider when making treatment decisions.

Atonic seizures are characterized by a sudden loss of postural muscle tone resulting in a rapid fall to the ground (if walking) or collapse at the waist (falling forward or backwards if sitting). Clinically, it appears as though the child went suddenly limp, with no effort made to catch or protect themselves. These last only a few seconds, and the child is usually recovering immediately after the fall. Sometimes, these are limited to the head, resulting in head drop or nods only.

Many atonic seizures are associated with an initial myoclonic component (myoclonic-atonic seizure). The myoclonic component is recognized by the sudden shock-like, jerk of the body. This lasts only a fraction of a second. However, myoclonic-atonic seizures may be seen in other epilepsy syndromes, such as Doose Syndrome, that do not necessarily progress to LGS. As a result, the presence of drop attacks does not confirm the diagnosis of LGS.

Other Seizure Types

In addition to the common seizure types described above, other seizure types are common. Some may occur more frequently in adolescents and adults, or occasionally before the characteristic seizure types (further complicating the diagnosis of LGS).

Partial onset seizures with or without secondary generalization, generalized tonic-clonic seizures and one-sided clonic seizures are common. Partial-onset seizures may be characterized by staring with a slow decrease in muscle tone (slump) and unresponsiveness, lasting 30 to 60 seconds. These may progress to a full body, convulsive seizure (generalized tonic-clonic) with an initial brief stiff phase (tonic), followed by jerking in both arms and legs (usually more in the arms) (clonic phase) with bluish discoloration around the mouth. The convulsive phase typically lasts from 45 to 90 seconds. The seizure may begin as a generalized tonic-clonic event, without the prior partial phase, and if it does, is more dangerous to the patient, as there is no warning and may result in a fall with injury. As the child reaches adolescent or early adult years the seizure types may change into more complex partial and generalized tonic-clonic, however, the tonic seizures occurring in sleep typically persist into adulthood.

Status Epilepticus

Most patients with LGS will have one or several episodes of status epilepticus (a series of seizures, without return to the child’s normal state, lasting 30 minutes or longer). This may consist of a mixture of atypical absence, tonic and other seizure types. These seizures often take days to weeks for the child to recover from and likely contribute to the progressive intellectual decline. Every patient with LGS should have an emergency treatment plan that is tailored to their seizures and access to emergent medical care. This should be reviewed periodically with the family and communicated to their primary care physician.

Author: James Wheless, M.D.
Topic Editor: Robert Fisher, M.D., Ph.D.
Last Reviewed: 8/7/09