Absence status epilepticus is a prolonged, generalized absence seizure that usually lasts for hours and can even last for days. The cardinal symptom is the altered state of consciousness while the patient is usually fully alert and partially responsive. Absence status epilepticus may be typical, occurring in patients with idiopathic generalized epilepsy, or atypical, occurring in patients with neurocognitive impairment as with developmental and epileptic encephalopathies. Absence status epilepticus may also appear de novo, mainly in adults without a previous history of epilepsy. Absence status epilepticus is often misdiagnosed as focal status epilepticus or a confusional nonepileptic condition or epileptic prodrome. Frequently, absence status epilepticus occurs in the setting of medication nonadherence or because of ill-advised antiepileptic drug treatment, such as with tiagabine or carbamazepine in patients with idiopathic generalized epilepsy.
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• Absence status epilepticus is a prolonged, generalized absence seizure that usually lasts for hours and can even last for days.
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• The cardinal symptom is the altered content of consciousness while the patient is usually fully alert and partly responsive.
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• Most patients suffer from idiopathic generalized epilepsy, but absence status epilepticus may also appear de novo. Other types of seizure such as absences, myoclonic jerks, and generalized tonic-clonic seizures may predate the first occurrence of absence status epilepticus for many years.
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• Absence status epilepticus is often misdiagnosed as focal status epilepticus, confusional nonepileptic condition, or epileptic prodrome.
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• Medication nonadherence is a common trigger for the occurrence of absence status epilepticus.
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• Frequently, absence status epilepticus occurs because of ill-advised antiepileptic drug treatment such as tiagabine, carbamazepine, gabapentin, oxcarbazepine, pregabalin, or vigabatrin.
Historical note and terminology
According to Wolf and colleagues, the first historical case of absence status epilepticus seems to be described on an ex-voto table of 1501 in the parish church of Gmünd in Austria of an ancestor of a family with onset of typical absence seizures in childhood and subsequent generalized tonic-clonic seizures (106).
The first unequivocal documentation of absence status epilepticus with EEG was by Putman and Merritt (74) and Lennox (55). Prolonged episodes of nonconvulsive status epilepticus were described on many occasions before the EEG-era, most of which may have been of focal origin (temporal lobe) (85; 82).
Absence status epilepticus is the name proposed by the Commission on Classification and Terminology of the International League Against Epilepsy (21; 22). Absence status is not synonymous with nonconvulsive status epilepticus. Nonconvulsive status epilepticus is a term that rightly has been discarded in the new ILAE diagnostic scheme because it encompasses heterogeneous conditions, which may be focal, such as limbic status epilepticus, or generalized, such as absence status epilepticus (31; 30; 60; 64). According to an expert consensus, "nonconvulsive status epilepticus is a term used to denote a range of conditions in which electrographic seizure activity is prolonged and results in nonconvulsive clinical symptoms” (102). However, convulsive elements and, particularly, myoclonic jerks are common in generalized nonconvulsive status epilepticus, as in eyelid or perioral absence status epilepticus. If the term “nonconvulsive” is used, the distinction between “focal nonconvulsive” and “generalized nonconvulsive” should be made for clinical and management purposes (37; 35). Petit mal status epilepticus and various other synonyms have also been used in the past. Unified EEG terminology and criteria for nonconvulsive status epilepticus have been proposed (14), and its various types, including absence status epilepticus, have been systematically classified (90).
Classification. Considering that absence status epilepticus is a prolonged absence seizure, it is reasonable to adopt for this condition a definition and classification similar to that recognized for epileptic seizures and syndromes manifested with absences (22; 66; 64; 31; 30; 84; 102; 54; 41; 40).
Table 1. Classification of Absence Status Epilepticus
Typical absence status epilepticus
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(Typical) absence status epilepticus in order of prevalence:
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• Simple absence status epilepticus (mainly in idiopathic generalized epilepsy and juvenile absence epilepsy)
• Perioral myoclonic absence status epilepticus
• Eyelid myoclonic absence status epilepticus
• Myoclonic absence status epilepticus
• Other types of simple or complex absence status epilepticus (fixation-off-sensitive idiopathic generalized epilepsy with mainly catamenial absence status epilepticus; photosensitive idiopathic generalized epilepsy with absences
Absence status epilepticus of developmental or epileptic encephalopathies including Lennox-Gastaut syndrome
Situation-related absence status epilepticus due to:
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I. Benzodiazepine withdrawal
II. Electrolyte and other metabolic disturbances
III. GABA agonist-induced absence status epilepticus in patients with epileptic seizures (tiagabine or vigabatrin)
IV. Severe brain anoxia in comatose or critically ill patients
Absence seizures are broadly divided into: (1) typical absences of mainly idiopathic generalized epilepsy with generalized, greater than 2.5 Hz spike or polyspike-and-slow waves, and (1) atypical absences in developmental and epileptic encephalopathies with slower, less than 2.5 Hz generalized discharges (21; 79). The ILAE classification of seizure types classifies all absences as “nonmotor seizures of generalized onset” as follows: typical, atypical, myoclonic, and eyelid myoclonia absences (41; 40).
Similarly, absence status epilepticus is divided into typical absence status epilepticus of mainly idiopathic generalized epilepsy and atypical absence status epilepticus of developmental or epileptic encephalopathies.
Furthermore, to comply with seizure and syndrome classification, absence status epilepticus may be situation-related and caused by the introduction or withdrawal of certain drugs, intoxication, or electrolyte or metabolic disturbances. Symptomatic absence status may also be caused by severe brain anoxia or other brain damage.
ILAE Task Force classification. The ILAE Task Force report (30) classifies absence status epilepticus as:
(A) Typical and atypical absence status epilepticus. When absence status epilepticus occurs in the idiopathic epilepsies, it has features similar to atypical absence and can be terminated by antiepileptic drugs. In the developmental and epileptic encephalopathies, there is overlap with focal status epilepticus due to lesions of certain frontal lobe areas. The absence status epilepticus occurring in elderly patients without a prior history of epilepsy, as well as drug-induced and drug-withdrawal absence status epilepticus, have been characterized and most likely represent similar mechanisms; however, there may be several types of typical and atypical absence status epilepticus.
(B) Myoclonic absence status epilepticus. Myoclonic absence status epilepticus consists of proximal, predominantly upper extremity myoclonic jerks corresponding with 3 Hz spike-wave discharges in the EEG. It can last hours or even days and is usually resistant to therapy.