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  • Updated 05.19.2023
  • Released 02.26.2013
  • Expires For CME 05.19.2026

Generalized onset tonic-clonic seizures



Generalized onset tonic-clonic seizures are the most dramatic, severe, and common seizures of mainly syndromes of idiopathic generalized epilepsy. They manifest with violent generalized convulsions, loss of consciousness, and marked autonomic disturbances. They are usually spontaneous, but they may also be provoked by external, mainly photic, stimuli. They occur at any time, but mainly on awakening. They are often associated with severe complications that may also be fatal. They affect patients of all ages, except neonates. Additionally, patients may also suffer from other types of seizures, such as absences and myoclonic jerks. Syncope and psychogenic nonepileptic seizures are frequently misdiagnosed as generalized onset tonic-clonic seizures. Treatment is demanding because a significant number of currently available antiepileptic drugs may aggravate generalized seizures. In this updated article, the author details the clinical manifestations, pathophysiology, EEG, and neuroimaging of generalized onset tonic-clonic seizures and provides clues for correct diagnosis and optimal management of patients.

Historical note and terminology

Historical aspects. The manifestations of GTCS are so dramatic that accurate descriptions can be found as early as 1050 BC in the twenty-fifth Babylonian cuneiform tablet devoted to miqtu (a disease in which the person loses consciousness and foams at the mouth) (05). A realistic depiction of GTCS, including marked cyanosis, can be seen in the painting The Miracles of St Ignatius of Loyola (1617) by Peter Paul Rubens (1577-1640) (79).

Gowers gives an excellent description of GTCS (38):

At the onset of the severe fit the spasm is tonic in character, – rigid, violent, muscular contraction, fixing the limbs in some strained position… When the cyanosis has become intense, the fixed tetanic contractions of the muscles can be felt to be vibratory, and the vibrations gradually increase until there are slight visible remissions. As these become deeper, the muscular contractions become more shock-like in character… Such attacks may commence with tonic spasm, or they may commence by, and sometimes consist only of clonic spasm… Precursory symptoms occasionally precede a fit, sudden jerks of the body or limbs.

However, it was Henri Gastaut and his associates in Marseilles, France who provided us with superb descriptions of the clinical and EEG manifestations of GTCS, which have not been surpassed (33). Their description was based on a large number of combined clinical, EEG, and polygraphic investigations of GTCS in patients with epileptic disorders or induced by Metrazol or electroconvulsive treatment of psychotic patients. These were supplemented by cinematographic or videotaped filming and various other techniques. Contributions have been made with video-EEG analysis (57; 10).

ILAE classification and nomenclature. A fundamental distinction of all ILAE classifications is whether tonic-clonic seizures are of generalized or focal onset (25; 24; 04; 15; 29; 28).

According to the ILAE definitions, generalized seizures “originate at some point within, and rapidly engage, bilaterally distributed networks. Such bilateral networks can include cortical and subcortical structures, but do not necessarily include the entire cortex. Although individual seizure onsets can appear localized, the location and lateralization are not consistent from one seizure to another. Generalized seizures can be asymmetric.” Conversely, focal seizures “originate within networks limited to one hemisphere, which may be discretely localized or more widely distributed. Focal seizures may originate in subcortical structures” (04; 15; 29; 28).

The ILAE description of GTCS in the 1981 proposal is as follows (14):

The most frequently encountered of the seizures are GTCS, often known as grand mal. Some patients experience a vague ill-described warning, but the majority lose consciousness without any premonitory symptoms. There is a sudden, sharp tonic contraction of muscles, and when this involves the respiratory muscles, there is stridor, a cry or moan, and the patient falls to the ground in the tonic state, occasionally injuring him or herself. The patient lies rigid, and during this stage, tonic contraction inhibits respiration and cyanosis may occur. The tongue may be bitten and urine may be passed involuntarily. This tonic stage then gives way to clonic convulsive movements lasting for a variable period of time. During this stage, small gusts of grunting respiration may occur between the convulsive movements, but usually the patient remains cyanotic and saliva may froth from the mouth. At the end of this stage, deep respiration occurs and all the muscles relax, after which the patient remains unconscious for a variable period of time and often awakes feeling stiff and sore all over. He or she then frequently goes into a deep sleep and when awakened feels quite well apart from soreness and, frequently, headache. GTCS may occur in childhood and in adult life; they are not as frequent as absence seizures, but vary from daily to once every 3 months and occasionally to one every few years. Very short attacks without postictal drowsiness may occur on occasion.

GTCS are defined as follows in the ILAE glossary (07):

Generalized tonic-clonic seizure (synonym: bilateral tonic-clonic seizure--formerly “grand mal” seizure, noun): bilateral symmetrical tonic contraction, then bilateral clonic contractions of somatic muscles usually associated with autonomic phenomena.

Note that the terms “primarily” and “secondarily” GTCS should not be confused with the now obsolete terms of “primary” and “secondary epilepsy,” which have been rightly abandoned by the ILAE and by most physicians, though they are often used in formal reports of antiepileptic drug trials. Additionally, these terms are not used in the ILAE glossary (07). Furthermore, “primarily” and “secondarily” GTCS have been abolished in the ILAE definitions and “secondarily generalized tonic-clonic” has been replaced by “focal to bilateral tonic-clonic” (29; 28).

In the 2014 ILAE “Epilepsy diagnosis” manual, generalized onset tonic-clonic seizures are categorized amongst generalized convulsive seizures (15). Generalized seizures are convulsive, absence, tonic, atonic, and myoclonic.

“Generalized convulsive seizures are typically bilateral and symmetric although variants with asymmetry including head and eye deviation can be seen. A tonic clonic seizure is a seizure consisting of a tonic and a clonic phase, typically in this order, however variations such as clonic-tonic-clonic are also seen. A clonic seizure is a seizure involving bilaterally rhythmic jerking and may occur alone or in combination with tonic activity where there is bilaterally increased tone of the limbs typically lasting seconds to a minute. The jerking in a clonic seizure is more sustained and rhythmic than seen in a myoclonic seizure” (15).

The most recent ILAE positional papers on the operational classification of seizure types retain the name “generalized onset tonic-clonic seizures” and classify them amongst “generalized onset motor seizures” (29; 28). Generalized onset seizures are motor (tonic-clonic, clonic, tonic, myoclonic, myoclonic-tonic-clonic, myoclonic-atonic, atonic, epileptic spasms) or nonmotor (absence) (typical, atypical, myoclonic, eyelid myoclonia). GTCS are defined as follows (29; 28):

“bilateral symmetric or sometimes asymmetric tonic contraction and then bilateral clonic contraction of somatic muscles, usually associated with autonomic phenomena and loss of awareness. These seizures engage networks in both hemispheres at the start of the seizure. Generalized myoclonic-tonic-clonic seizures begin with a few myoclonic jerks followed by tonic-clonic activity. These seizures are commonly seen in patients with juvenile myoclonic epilepsy and occasionally with other generalized epilepsies. It is arguable whether the initial jerks are myoclonic or clonic, but they are rarely sufficiently sustained to be considered clonic. Because there is a new seizure type (myoclonic-tonic-clonic) characterized by myoclonic movements preceding tonic (stiffening) and clonic (sustained rhythmic jerking) movements, it is important to document the early movements of a tonic-clonic seizure as being tonic. The clonic phase of a tonic-clonic seizure typically shows regularly decreasing frequency of jerks over the course of the event. During a tonic-clonic seizure, awareness is lost before or contemporaneously with the stiffening and jerking movements. Some tonic-clonic seizures may invoke a nonspecific feeling of an impending seizure or a brief period of head or limb version, neither of which invalidates a generalized onset, since biologic processes never exhibit perfect synchrony. The clinician has to judge whether a truly focal onset is present.”

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