How are seizures characterized in Lennox-Gastaut syndrome (LGS)?

Updated: Nov 09, 2018
  • Author: Koshi A Cherian, MD; Chief Editor: Amy Kao, MD  more...
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Answer

Tonic seizures have a frequency of 17-95%. These seizures can occur during wakefulness or sleep but are more frequent during non–rapid eye movement (REM) sleep. Duration is from a few seconds to a minute.

Tonic seizures can be axial, axorhizomelic, or global. Axial tonic seizures involve the head and trunk with head and neck flexion, contraction of masticatory muscles, and eventual vocalizations. Axorhizomelic tonic seizures feature tonic involvement of the proximal upper limbs with elevation of the shoulders and abduction of the arms. Global tonic seizures are marked by contraction of the distal part of the extremities, occasionally leading to a sudden fall and at other times mimicking infantile spasms.

Tonic seizures can be asymmetric. Some patients may show gestural automatisms after the tonic phase. The tonic seizure may end in a vibratory component if prolonged.

Atypical absence seizures range in frequency from 17-100%. This wide range results from parental inability to correctly recognize and identify atypical absences. In one study using video/EEG monitoring in a cohort of children with LGS, parental recognition was 27% for atypical absences, while the sensitivity was as high as 80% for myoclonic seizures and 100% for tonic, atonic, tonic-clonic, clonic, and complex partial seizures.

Atypical absences may be difficult to diagnose because their onset may be gradual and loss of consciousness may be incomplete, allowing the patient to continue activities to some degree. Patients may have associated eyelid myoclonias, which are not as rhythmic as in typical absences but often are associated with perioral myoclonias or progressive flexion of the head secondary to a loss of tone. Automatisms may be observed. Seizures may end gradually in some patients and abruptly in others.

Atonic seizures, massive myoclonic seizures, and myoclonic-atonic seizures have a frequency of 10-56% in LGS. These seizures are difficult to differentiate by clinical observation only. Considerable discrepancies exist in the use of these terms. All 3 types can produce a sudden fall, producing injuries (drop attacks, Sturzanfälle) or may be limited to the head falling on the chest (head drop, head nod, nictatio capitis). Pure atonic seizures are exceptional; most have a tonic or myoclonic component.

Other types of seizures are noted. Generalized tonic-clonic seizures are reported in 15% of patients, while complex partial seizures occur in 5%. Absence status epilepticus, tonic status epilepticus, and nonconvulsive status epilepticus all can occur and can be resistant to therapy.


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