Pearls, Perils, and Pitfalls In the Use of the Electroencephalogram

Omkar N. Markand, MD, FRCPC

Disclosures

Semin Neurol. 2003;23(1) 

In This Article

Abstract and Introduction

Abstract

Despite advances in neuroimaging techniques over the past three decades that have helped in identifying structural lesions of the central nervous system, electroencephalography (EEG) continues to provide valuable insight into brain function by demonstrating focal or diffuse background abnormalities and epileptiform abnormalities. It is an extremely valuable test in patients suspected of epilepsy and in patients with altered mental status and coma. Patterns in the EEG make it possible to clarify the seizure type; it is indispensable for the diagnosis of nonconvulsive status epilepticus and for separating epileptic from other paroxysmal (nonepileptic) episodes. There are EEG patterns predictive of the cause of the encephalopathy (i.e., triphasic waves in metabolic encephalopathy) or the location of the lesion (i.e., focal polymorphic delta activity in lesions of the subcortical white matter). The various EEG characteristics of infantile, childhood, and adult epilepsies are described as well as the EEG patterns that are morphologically similar to interictal/ictal epileptiform discharges but unrelated to epilepsy. An EEG is most helpful in determining the severity and, hence, the prognosis of cerebral dysfunction. Lastly, EEG is extremely helpful in assessing normal or abnormal brain functioning in a newborn because of the serious limitation in performing an adequate neurologic examination on the neonate who is intubated or paralyzed for ventilatory control. Under such circumstances, the EEG may be the only available tool to detect an encephalopathic process or the occurrence of epileptic seizures.

Introduction

Electroencephalography (EEG) is the technique of recording from the scalp the spontaneous electrical activity of the brain and correlating it to the underlying brain function. Since the first recording of a human EEG in 1929 by Hans Berger, improvement in electronics and technology has made EEG one of the most widely used laboratory tests for clinical evaluation of neurologic disorders. However, in the past three decades with continuing advances in neuroimaging, particularly magnetic resonance imaging (MRI), the role of clinical EEG has become restricted and progressively more focused. Its major utility at present is in the evaluation of focal and diffuse encephalopathies, comatose conditions, epileptic disorders, and cerebral disorders affecting neonates and infants. The present article is not an attempt to describe EEG comprehensively in normal subjects and in different disease processes but to highlight its usefulness/limitation and emphasize precautions/care needed in its optimal utility. The subject will be discussed under seven sections: EEG in normal subjects, EEG in patients with altered mental status or diffuse encephalopathies, EEG in focal or lateralized cerebral hemispheric lesions, EEG in paroxysmal disorders, EEG in generalized epilepsies, EEG in neonates, and EEG in status epilepticus.

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