The electroencephalogram (EEG) provides important information to aid clinicians in the diagnosis of epilepsy. However, EEG techniques are associated with certain limitations, as discussed in the presentation by Bradley V. Vaughn, MD.
Published Online: June 03, 2013
Bradley V. Vaughn, MD, vice chair of neurology and the chief of the division of sleep and epilepsy at the University of North Carolina School of Medicine, discussed epileptiform activity in ictal and interictal discharges. Vaughn noted a cluster of features observed in patients with epilepsy and provided the audience a glimpse into how video polysomnography may help to identify seizures. He polled the audience about how easily epileptiform discharges were identified, and very few audience members indicated complete comfort in identifying these phenomena. Vaughn proceeded to outline electroencephalogram (EEG) readings, interictal discharges, and possible pitfalls in identifying interictal discharges.
Continuing, Vaughn described epilepsy as a group of disorders characterized by recurrent epileptic seizures. Seizures include any sudden morbidity event, either sensory or motor, and epileptic seizures include pathologic, synchronous neuronal firing. An estimated 1% of the population has epilepsy, but only 60% of those people have epileptiform discharges. About 2% of the general population experiences epileptiform discharges in the absence of seizure disorder. In sleep-deprived patients with epilepsy, the percentage of patients with observable discharges associated with epilepsy climbs to 80%. Although the EEG aids the clinician enormously, Vaughn noted the diagnostic limitations of EEG techniques, and so other clinical clues are often used to confirm the diagnosis. Vaughn described the term epileptogenic as a descriptor of brain electrical discharges that appear to be the start of a seizure, with interictal discharges being those that occur between seizures. The brain’s neurons are similarly oriented in the cortex. There are many synapses, and the summation gives us the EEG. However, the waves on the EEG have no relationship to the synaptic potential of the cell body. The EEG signal does not come from individual brain cells nor the axons of those cells, but from a summation of the signals of many neurons.
Vaughn explained that reading an EEG involves pattern recognition. An abnormality must be seen multiple times on the EEG for recognition of a seizure disorder. However, at the same time, the physician must recognize all the small details in the context of a large amount of data. However, even with a full set of electrodes, Vaughn explained that over 40% of the brain may be missed, and thus a discharge might not occur in the right place in the brain for the physician to recognize it. Without electrodes in the right area, the physician might not read any signal, even if one is occurring.
Nocturnal seizures occur predominantly in the frontal and temporal lobes. Vaughn proceeded to show instances of nocturnal seizures. Although the videos of patients experiencing seizures did not appear “seizure-like” to most members of the audience, Vaughn revealed that all 3 videos had indeed depicted seizures. He then emphasized that seizures occur fairly commonly, with 1 in 10 people experiencing a seizure at some point in their lifetime.
He explained, “What the brain can do as part of a seizure is anything that a person can do in normal function. You can see some complex behavior. Patients may get up and run, take their clothes off, or have conversations.” Vaughn stated that patients experiencing temporal lobe seizures do not move very much, but they may experience deja-vu, out-of-body experiences, olfactory experiences, and psychic events.
Seizures can occur during sleep and may include somatosensory components. Objects may look larger or smaller than usual, which is known as Alice in Wonderland syndrome. Additionally, brief tonic seizures, which can last between 5 and 7 seconds, may occur during sleep. Even in a sleep study, these seizures are easy to miss because they are brief. Vaughn proceeded to show the audience several videos. In one, a gentleman sat up, took the cord of the EEG machine, and used it like a lasso. He then stopped, sipped his coffee, went back to whipping the cord, and then waved off the nurse. The man’s left hand, Vaughn pointed out, showed posturing. Although the EEG was unreadable, the man did not have impairment of consciousness, which indicated a partial seizure.
In another case, a woman showed arching of her back. The violent movement of the woman had broken the jaw of an attending physician at a previous hospital where she had been monitored. The lesson from this, Vaughn explained, is that physicians should not wait to see abnormalities on the EEG before noticing the symptoms that are consistent with epilepsy. The patient was monitored during 8 episodes of seizures before an EEG abnormality occurred.
Another female patient demonstrated nocturnal wandering. She would be found between 1 and 5 miles from her home on occasion. Vaughn demonstrated that aggressive interactions could result in serious harm to a caregiver attempting to wake a patient who is wandering from home while asleep. Regarding these patients, this feature is important to remember because training a caregiver may help to avoid violence and trauma inflicted by a sleeping individual who is wandering while experiencing a seizure.
Vaughn then showed the brevity of absence seizures, which lasted just a few seconds. He indicated that these episodes can occur hundreds of times daily in patients who experience absence seizures. Momentary changes in breathing also occurred in other patients. Atonic seizures, by contrast, include falling and generally cannot be observed in sleep because patients are already laying down while asleep. However, tonic posturing with trembling may also occur in atonic seizures that take place during sleep. Myoclonic seizures usually occur in the early morning hours, and Vaughn proceeded to show a video of a patient experiencing myoclonic seizures, explaining that each jerk of the patient’s body was an individual seizure.
Summarizing his presentation, Vaughn emphasized that anything the brain can do may be part of a seizure—even paroxysmal events. Most seizures last under 5 minutes and 90% of seizures last less than 3 minutes. The EEG, as Vaughn explained, should “tell a story, with a beginning, middle, and an end.” Vaughn impressed upon the audience that a single EEG abnormality, without other supporting evidence, does not constitute epilepsy.