Tonic status epilepticus is a serious, sometimes fatal, epileptic condition that may last for days or even months and occurs mainly in children with neurocognitive impairment and severe epilepsy, such as Lennox-Gastaut syndrome. Tonic status epilepticus in these children comprises repetitive frequent tonic seizures. Characteristically, as the status progresses, motor symptoms tend to lessen whereas autonomic disturbances, including respiratory depression, become more prominent. At final stages, there may be only electrographic evidence of tonic seizures. Video-EEG monitoring is usually mandated for the recognition of autonomic status epilepticus, particularly when motor manifestations are minimal. Treatment is demanding, and the intravenous administration of benzodiazepines may be of some concern because of a few reports that these may induce tonic status epilepticus; newer antiepileptic drugs such as lacosamide have been reported as effective. Unfortunately, the only systematic studies of tonic status epilepticus are dated 40 years ago. The author reviews the limited information on clinical manifestations, investigative procedures, pathophysiology, and optimal but anecdotal management of patients with tonic status epilepticus.
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• Tonic status epilepticus manifests with repetitive series of frequent tonic seizures that may last for weeks or months.
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• As the status progresses, autonomic manifestations, including respiratory depression, predominate and may lead to death.
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• Video-EEG monitoring may be mandatory.
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• This condition occurs nearly exclusively in children with neurocognitive impairment and mainly in those with Lennox-Gastaut syndrome.
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• Emergency treatment is anecdotal though newer antiepileptic drugs, such as lacosamide, appear promising.
Historical note and terminology
Tonic status epilepticus has been nearly exclusively studied systematically by Henri Gastaut and his Marseille School of epileptology (26; 24; 54; 45). Their classical work still remains the main source of information on the topic.
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Tonic status epilepticus. This variety is more frequent in children. The tonic spasms are repeated at a rate of four to twenty per hour and may progressively attenuate until no motor expression persists except recurrent superior conjugate deviation of the eyes. At this point, the attacks are usually recognized only if the EEG is monitored, but the autonomic phenomena continue and may even undergo progressive increase to terminate, during a period of relatively intact consciousness, in death from respiratory or cardiovascular failure (24).
The ILAE proposal of 1989 refers to status epilepticus of Lennox-Gastaut syndrome as “frequent (stuporous states with myoclonias, tonic, and atonic seizures)” (11). The ILAE Task Force on classification classified tonic status epilepticus with other generalized types of status epilepticus (15) and gave the following description “Tonic status epilepticus most commonly occurs in patients with symptomatic generalized epilepsy but may occur in patients with idiopathic generalized epilepsy. In some of these patients, there appears to be an overlap of symptoms of idiopathic and symptomatic generalized epilepsy. Characteristically, when the patient is lying down, the neck is flexed, and the arms are flexed at the elbow and slightly elevated. The tonic spasms are brief and can continue at brief intervals for hours. In symptomatic generalized epilepsy the duration of the status epilepticus can be much longer” (16).
The new ILAE proposal and the ILAE position papers on seizures and classification have not dealt with status epilepticus (05; 19; 47). However, the ILAE Task Force on the Classification of Status Epilepticus has now published its report on “a definition and classification of status epilepticus” that encompasses all types of status epilepticus, and it takes into consideration current knowledge regarding its pathophysiology and the need to address clinical treatment decision making time points, as well as the conduct of epidemiologic and clinical studies (56). Accordingly, “status epilepticus is a condition resulting either from the failure of the mechanisms responsible for seizure termination or from the initiation of mechanisms, which lead to abnormally prolonged seizures (after time point t1). It is a condition that can have long-term consequences (after time point t2), including neuronal death, neuronal injury, and alteration of neuronal networks, depending on the type and duration of seizures” (56). This definition is conceptual, with 2 operational dimensions: the first is the length of the seizure and the time point (t1) at which the seizure should be regarded as an “abnormally prolonged seizure.” The second time point (t2) is the time of ongoing seizure activity beyond which there is a risk of long-term consequences. In the case of convulsive (tonic-clonic) status epilepticus, both time points are based on animal experiments and clinical research. This evidence is incomplete; furthermore, there is considerable variation, so these time points should be considered as the best estimates currently available. Data are not yet available for other forms of status epilepticus, but as knowledge and understanding increases, time points can be defined for specific forms of status epilepticus based on scientific evidence and incorporated into the definition, without changing the underlying concepts. This division into 2 time points has clear clinical implications: the time point of operational dimension 1 determines the time at which treatment should be considered or started, whereas the time point of operational dimension 2 determines how aggressively treatment should be implemented to prevent long-term consequences. The time domain may vary considerably between different forms of status epilepticus. This new report provides no description or time points (t1 or t2) of tonic status epilepticus, which is simply classified among other types of status epilepticus with prominent motor features that occurs in Ohtahara, West, and Lennox-Gastaut syndrome (56).
Shorvon considers tonic status epilepticus amongst “nonconvulsive status epilepticus occurring in both childhood and adult life with epileptic encephalopathy: (3a) Nonconvulsive status epileptic in the Lennox-Gastaut syndrome (i) Atypical absence status epilepticus (ii) Tonic-status epilepticus” (49).
In the American Academy of Neurology practice parameter, tonic status epilepticus is cited amongst “convulsive status epilepticus that occurs with overt clinical signs, such as tonic, tonic-clonic, or clonic motor movements. Nonconvulsive status epilepticus occurs when either electrographic status epilepticus is associated with altered awareness without overt clinical signs, or altered awareness with subtle motor signs, such as minimal eyelid blinking” (44).
The 2014 ILAE “Epilepsy Diagnosis” manual has not dealt with status epilepticus (12); generalized onset tonic seizures are categorized as 1 of the 5 types of generalized seizure (convulsive, absence, tonic, atonic, myoclonic) and are described as follows:
A generalized tonic seizure involves bilaterally increased tone of the limbs typically lasting seconds to a minute. They often occur out of sleep and in runs of varying intensity of tonic stiffening. The individual is unaware during these events. At the beginning of tonic seizures with more intense stiffening, individuals may make an expiratory sound. More severe and prolonged tonic seizures may have a vibratory component, which may be confused with clonic jerking. Tonic seizures often occur in individuals with intellectual impairment.
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Caution. Although asymmetry can occur in a generalized tonic seizure, if consistent focal features are seen from seizure to seizure, then consider focal seizure involving the frontal lobe.
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Note. Tonic seizures are one type of seizure that can result in a “drop attack” (also known as astatic seizure); other causes of drop attacks include myoclonic (especially in younger children), atonic, and myoclonic-atonic seizures.
EEG background/interictal/activation. Please refer to specific syndromes and etiologies in which this seizure type occurs.
EEG ictal. Tonic seizures show diffuse or generalized accelerating low amplitude paroxysmal fast activity, which is often bilateral and predominates in the anterior and vertex regions.
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Caution. Consistent focality of spikes or maximal amplitude of ictal rhythm, then consider focal seizure.
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• Epileptic spasms: The motor contraction is often shorter in duration (< 2 seconds); epileptic spasms often occur in a series.
• Focal seizure: Supplementary sensorimotor cortex of frontal lobe
• Nonepileptic seizures
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• Lennox-Gastaut syndrome
• Epilepsy with myoclonic-atonic seizures
Adapted from (12).