Chapter 26: Absence Status Epilepticus

Introduction

The term nonconvulsive status epilepticus (SE) is used to describe a situation in which there is prolonged electrographic seizure activity that results in an alteration of consciousness or behavior, without convulsive movements.¹ Because many other conditions can result in altered mentation, an electroencephalographic (EEG) pattern consistent with nonconvulsive status is needed to confirm this diagnosis. However, the exact EEG changes necessary for diagnosis must be clearly stipulated, as EEG may show epileptiform activity associated with similar cognitive and behavioral changes in cases that are not in nonconvulsive SE.

Kaplan proposed the following definition of nonconvulsive SE, which takes into account both clinical and electrographic criteria:²

1. Altered consciousness or behavior from the baseline state for at least 30 minutes without convulsive movements

   and

2. The presence of one or more of the following epileptiform patterns:

   1. Repetitive focal or generalized epileptiform activity (spikes, sharp waves, spike and wave, sharp and slow-wave complexes) or rhythmic theta or delta at more than 2 per second

   2. The above EEG patterns at less than one per second, but with improvement or resolution of epileptic activity and improvement of the clinical state following intravenous (IV) injection of a rapidly acting antiepileptic drug (AED), such as benzodiazepine

   3. A temporal evolution of epileptiform or rhythmic activity at more than one per second with change in location or frequency over time

Nonconvulsive SE encompasses both generalized nonconvulsive SE, including absence SE and myoclonic SE, and localization-related or focal subtypes. This chapter will focus on absence SE.

Clinical Categorization

The differentiation of complex partial SE from absence SE on clinical grounds alone can be difficult; however, some clinical distinctions have been described. In absence SE, alteration of contact with the environment is more continuous, in contrast to the cyclic variations in responsiveness levels that may be seen in complex partial SE.³ Motor signs in absence SE consist of generalized myoclonus compared with more focal or lateralized findings, such as head or eye version, focal limb posturing, or focal weakness in complex partial SE. Prominent fear, anxiety, irritability, and speech and memory difficulties are more suggestive of complex partial than absence SE. Finally, whereas automatisms may be seen in both absence and complex partial SE, prominent lip smacking and lateralized automatisms would suggest the latter.

Patients with absence SE can be divided into several distinct subgroups:

1. Persons with typical absence SE and a history of idiopathic generalized epilepsy

2. Persons with atypical absence SE and a history of symptomatic generalized epilepsy

3. Adults who present de novo with typical absence SE and who frequently have coexistent metabolic dysfunction, infection, medication-related toxicity, or atrophy

4. Borderline cases, which look like generalized nonconvulsive SE but have some focal components, often in the context of a history of focal epilepsy, particularly frontal lobe epilepsy

Because these groups are clinically quite distinct, ...