Definition

SE is now defined in one of two ways: (1) as recurrent epileptic seizures without full recovery of neurologic function between the seizures, or (2) as continuous seizure activity lasting 30 minutes or more. If the first definition is used, then GCSE can be defined as recurrent generalized convulsions without complete recovery of neurologic function (usually assessed by level of consciousness) between seizures. However, if GCSE is allowed to continue untreated or is inadequately treated, so that seizure activity persists, there is an evolution from overt to subtle motor manifestations. This evolution has been described in both clinical (148, 155) and experimental (48, 89) GCSE. Overt GCSE is easily recognized as recurrent generalized convulsions without full recovery of neurologic function between seizures. In 1984 Treiman and colleagues (160) proposed that the term subtle generalized convulsive status epilepticus be used whenever a patient in GCSE exhibits profound coma and ictal discharges on the electroencephalogram (EEG), but only subtle rhythmic motor activity, such as focal twitches of the eyelid, face, jaw, trunk, or extremities, or nystagmoid jerks of the eyes. This concept of GCSE as a dynamic state, with evolution through progressive clinical stages from overt to subtle motor manifestations over time, was a rediscovery of a phenomenon first recognized by Bourneville in 1876 (12) in the first full clinical description of SE, and further elaborated by Clark and Prout in their extensive and detailed study of SE, published in 1903 and 1904 (22–24).

Although overt GCSE may evolve into subtle GCSE if inadequately treated, a history of overt GCSE is not essential to make the diagnosis of subtle GCSE. Sometimes subtle GCSE may appear de novo after a severe insult to the brain. Full motor expression of seizure activity appears to depend on a relatively healthy brain. The greater the degree of encephalopathy present, the more subtle is the convulsive activity. Thus, overt GCSE may evolve into subtle GCSE because inadequately treated seizure activity is itself encephalopathogenic, or GCSE may start with only subtle motor manifestations, if the episode of status is the result of some other encephalopathic insult. Patients who develop SE as a consequence of a severe insult to the brain (hypoxia, profound ischemia, severe CNS infection) may present with subtle or electrical GCSE. Privitera and colleagues (123) studied 29 patients with subtle GCSE; only 30% had a witnessed generalized tonic-clonic seizure prior to the onset of coma. Drislane and Schomer (32) identified 48 patients with “generalized electrographic status epilepticus” (ESE), which they considered similar to subtle GCSE; fewer than half of the patients had discrete convulsions preceding EEG identification of ESE. In the case of severe encephalopathy, there may be no motor activity observed. Some investigators have used the term nonconvulsive status epilepticus for this situation (29, 31, 32, 60, 82). However, Treiman suggested that this entity be labeled electrical GCSE (148, 149, 151, 155) or GCSE with electrographic seizures only (153), because such a presentation is the end-stage of the spectrum of clinical features that occur in GCSE during its evolution. Furthermore, the term nonconvulsive SE is used for SE with associated nonconvulsive seizures, such as complex partial SE and absence SE, in which the clinical presentation is of an epileptic twilight state and not the profound coma of end-stage GCSE (31, 61, 62, 77). Thus, there is danger of combining very different types of SE if patients with subtle GCSE are included. The term myoclonic SE has also been applied to some instances of subtle GCSE, which also creates the problem of combining dissimilar entities: (1) SE that is a complication of generalized myoclonic epilepsy (where consciousness is generally preserved) and (2) encephalopathy with epileptic myoclonus (where the patient is in profound coma). Therefore, Treiman (148) argued that the term myoclonic SE should be reserved for SE in myoclonic epilepsy. Not all patients with SE as a complication of an encephalopathic insult have epileptic myoclonus, but some do, and they probably have a different prognosis than other patients with subtle GCSE.