Donald W. Klass

The ictal bradycardia syndrome.

: Purpose: Episodic loss of consciousness presents a diagnostic challenge to the neurologist. A perhaps under‐recognized cause of episodic loss of consciousness, which we call the ictal bradycardia syndrome, occurs when epileptic discharges profoundly disrupt normal cardiac rhythm, resulting in cardiogenic syncope during the ictal event. We attempt to determine whether the presence of the ictal bradycardia syndrome provides localizing information regarding the site of seizure onset and to describe the demographics of patients with this syndrome. We also discuss difficulties in diagnosis and treatment.

EEG and Other Early Predictors of Epilepsy Remission: A Community Study

Summary: The course of seizures was reviewed in all 306 residents of Rochester, Minnesota who had epilepsy diagnosed between 1935 and 1978, lived in the region s ≫ 5 years after diagnosis, and had an electroencephalogram (EEG). The life‐table probability of having achieved 5 years seizure‐free (FYSF) by 20 years after diagnosis was 75%. In a multivariate proportional hazards model, these three variables predicted a significantly higher rate of achieving FYSF: no early‐life brain damage (remission rate ratio = 2.27, p < 0.01), no generalized epileptiform activity (rate ratio = 1.58, p < 0.05), and never having had a generalized tonic‐clonic seizure (rate ratio = 1.4, p < 0.05). The same three variables, plus age at diagnosis, were descriptors of the rate of reaching FYSF off medication. Gender, family history, type of seizure, and EEG findings other than generalized epileptiform activity were not significantly related to either end point. The predictor set did 15% better than prior probabilities in forecasting FYSF. Although informative about group experience, these predictors are weak clinical discriminators, singly or in a set. FYSF occurred in high proportion of even those persons whose history, clinical examination, or EEG findings placed them in a less favorable stratum of one or more predictors.

Electroencephalography of the elderly.

This review of the electroencephalography (EEG) of the elderly is concerned with definitions of terms; normal EEG variability during wakefulness, drowsiness, and sleep; paroxysmal activity; and EEG (including results of computerized spectral analysis) in selected disorders commonly affecting the elderly.

Interobserver variability in EEG interpretation

A random sample of 100 active electroencephalographers in the United States evaluated 10-second samples of 12 selected EEGs. The evaluations consisted of multiple-choice questions related to the age of the patient, EEG finding, artifact, and consciousness of the patient. The rate of reporting the “correct” response was examined in terms of various respondent characteristics such as EEG board certification, age, percent of time in clinical EEG work, and number of recordings interpreted annually. This study indicates that, even today, there is considerable variability in EEG interpretation, and that this variability is influenced by specific reader characteristics.

A distinctive rhythmic EEG discharge of adults

An unusual transient electroencephalographic pattern consisting of repetitive sharp-contoured wave forms in the range of 4--7 c/sec was seen in recordings from 65 patients who were between 42 and 80 years of age. This pattern was usually predominant over the parietal and temporal regions. No clinical alteration was associated with the pattern. Although the pattern resembled a subclinical EEG seizure discharge, it did not correlate with clinical seizures. The pattern occurred in patients with diverse clinical complaints, and although its mechanism of origin remains uncertain, it appears to represent a benign EEG phenomenon that has little diagnostic significance.

The diagnostic specificity of triphasic wave patterns

A blind analysis of 56 EEGs with triphasic wave patterns was performed to determine the diagnostic specificity of individual electrographic features. EEG and clinical variables analyzed included longitudinal topography, phase lags, symmetry, background activity, reactivity, longitudinal bipolar phase reversal sites, responses to photic stimulation and mental status at the time of recording. The only statistically significant finding for any of the diagnostic groups tested was the presence of severe background slowing in cases of hepatic encephalopathy (P less than 0.001). We found no evidence to suggest that other features may contribute to a more highly characteristic pattern for hepatic encephalopathy. None of the features studied reliably distinguished hepatic encephalopathy from other forms of metabolic encephalopathy.

Seizures induced by exercise

Three patients had a clinical history of epileptic seizures during exercise. In all three patients, generalized epileptiform EEG abnormalities were activated by exercise, whereas none had paroxysms during resting wakefulness or during hyperventilation, and only one had a paroxysmal discharge during sleep. Advice to epileptic patients about physical activity should be based on a careful history of individual tolerance. In doubtful cases, an EEG recorded during exercise can provide evidence for an epileptic mechanism.

Unusual EEG Patterns

Some of the unusual patterns that can be encountered on the EEG are described briefly. The patterns are grouped according to the predominant frequencies involved and/or by distinctive morphology or distribution. Those involving predominantly the alpha frequency range are alpha squeak, retained alpha, alpha-delta sleep, unilateral decrease in reactivity of alpha activity, and extreme spindles. The patterns involving the beta frequency range are the fast alpha variant, posterior temporal fast activity in children, the fast spiky spindle variant, central fast activity, and diffuse paroxysmal or continuous fast activity. The patterns of predominant theta frequencies are the slow alpha variant, frontal arousal rhythm, rhythmic temporal theta activity of drowsiness, midline theta rhythms, and focal parietal theta activity. Activity in the delta range includes the transient rhythmic slowing occurring after eye closure and the more continuous posterior rhythmic slowing. Patterns with a distinct morphology or distribution include the breach rhythm, wicket spikes, zeta waves, periodic frontal sharp complexes, subclinical rhythmic electrographic discharge of adults, and the EEG pattern of holoprosencephaly.

The Continuing Challenge of Artifacts in the EEG

ABSTRACT.From the very inception of EEG, the distinction between artifactual and cerebral electrical activity has been crucial. Dealing with artifacts effectively is an essential function of the EEG technologist and continues to be challenging. This review includes examples of common artifacts in unfamiliar guises, uncommon artifacts with identifiable characteristics, and some newer artifacts engendered by changing technology.

Infantile spasms, hypsarhythmia, and mental retardation. A study of etiologic factors in 61 patients.

The seizure disorder variously known as infantile spasms, lightning major seizures or massive myoclonic jerks was first described more than a century ago (14). It is characterized by a sudden, transient and usually repetitive contraction of most of the body musculature. Flexion is the most frequent pattern of movement, but extension, opisthotonus and tremor are also seen. The electroencephalographic pattern termed “hypsarhythmia” is a frequent finding, and mental retardation is almost invariably present. In about half the cases reported in the literature the cause is unknown, and in the remainder, brain injury related to birth or prenatal development and encephalitis are the presumptive etiologic factors invoked most commonly (5,7). In the present study, factors of possible importance in the etiology of this symptom complex are reviewed in a group of patients examined at the Mayo Clinic, some previously unrecognized causes are documented, and the mechanism and pattern of the infantile spasm are discussed.