Chapter 8: Auras and Other Simple Partial Seizures

Introduction

The classification of seizures according to whether consciousness is impaired is a major component of the commonly used convention outlined by the International League Against Epilepsy (ILAE) in 1981.¹ According to this system, partial seizures have initial clinical and electroencephalographic (EEG) evidence for localization to a neuronal system within one cerebral hemisphere. Partial seizures are then subcategorized as simple partial seizures (SPSs) and complex partial seizures (CPSs) based on whether the seizure produces an impairment of consciousness. If consciousness is not impaired, the seizure is considered simple partial. However, the matter of consciousness introduces a nuance to the classification that appears straightforward on a superficial level but actually may be difficult to implement. In the ILAE's 1981 system, consciousness is defined as the integrating activity by which a totality is grasped and incorporated into experience. This differs from vigilance, and consciousness is operationally defined as awareness and responsiveness to external stimuli and then recollection of the experience. Because consciousness is a philosophically and scientifically complicated matter, an operational definition is reasonable, but even this definition is problematic because impairment of consciousness is not binary. Impairment may involve components of consciousness and also may occur in gradations.²

With greater recognition of the problems inherent in classifying seizures according to consciousness, the ILAE proposed in 2001 that simple partial and complex partial cease to be classification terms.^3,4 In the new classification system, impairment of consciousness is one of many seizure descriptions but not the basis of seizure classification. Nevertheless, the simple partial classification endures and is commonly used, perhaps reflecting both tradition and the importance of consciousness as a key factor in assessing the clinical impact of a seizure. As such, this chapter will use the term simple partial seizure while still recognizing the term's limitations and proposed eventual elimination from the classification lexicon.

The distinction between SPS and CPS is further complicated by the common progression of an SPS to a CPS during one relatively brief episode. This possibility adds the diagnostic challenge of determining whether a seizure that is clearly an SPS at its onset becomes a CPS toward its resolution. However, the occurrence of an SPS at the onset of a CPS or a secondarily generalized seizure is also important for reasons beyond classification. Such seizures can provide a critically important warning for the patient. As has been known for millennia and described by Hippocrates, seizures may have early signs that allow patients to “know beforehand when they are about to be seized and flee from men, either to their homes or to a deserted place, and cover themselves up.”⁵ This integrity of awareness and responsiveness (consciousness) at the time of the seizure's symptomatic onset allows the patient an opportunity to minimize the impact of the seizure. During the SPS, the patient also may alert others of the seizure. This warning historically has been called an aura, originally ...