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The Use of Video EEG
A Valuable Tool in Diagnosis and Management of Seizures and Non-Epileptic Paroxysmal Spells
By Lanny Y. Xue, M.D., Ph.D., Division of Neurology/Epileptology
Our understanding of epilepsy has been greatly advanced by video EEG monitoring, which allows prolonged simultaneous recording of the patient’s behavior with the EEG. Seeing EEG and video data at the same time permits precise correlation between seizure activity in the brain and the patient’s behavior during seizures.
Video EEG recordings can be done on hospitalized inpatients or on outpatients, though the inpatient recording typically is of better quality as technologists are available to adjust electrodes and diminish outside activity that can interfere with the recording. We presently perform inpatient video EEGs at the New England Epilepsy Institute at Lawrence General Hospital, Lawrence, Mass. Video EEG has multiple important clinical applications. Patients with epilepsy, seizures, suspected seizures, suspected non-epileptic seizures, or recurrent spells (motor, sensory, autonomic, language, psychic, or consciousness or confusion) should undergo a video EEG study.
Confirming Clinical Suspicion of Epilepsy
A clinical suspicion of epilepsy can be confirmed by recording a seizure on video EEG. This is most likely to occur when the patient is experiencing frequent spells.
Detection of interictal epileptiform abnormalities in the absence of recorded seizures can provide supporting evidence for a clinical diagnosis of epilepsy. Ambulatory EEG studies have shown that between 35% and 38% patients with known seizures have epileptiform abnormality.
Video EEG is highly specific. Spikes are found on overnight video EEG in only 0.7% of asymptomatic adults without history of migraine or family history of epilepsy. In patients with a history of migraine headaches or a family history of epilepsy, the incidence of spikes on video EEG is 12.5% and 13.3%, respectively.
Some patients in whom epilepsy is suspected have a normal routine or sleep-deprived EEG. In these patients, video EEG can increase the chance of detecting an epileptiform abnormality.
Choosing Appropriate Antiepileptic Drugs
Video EEG monitoring can determine the type of epileptic seizure. Examples are differentiating absence from complex partial seizures or secondarily generalized from primary generalized convulsive seizures.
Seizure classification aids in the choice of treatments because different types of seizures may require different medical therapies. Patients with certain seizures may not need antiepileptic drugs (AEDs), some need treatment for a limited time interval, while others may need lifetime treatment with AEDs (e.g., juvenile myoclonic epilepsy). Seizure classification also has prognostic value. Seizure monitoring on video EEG may provide information about the patient’s response to antiepileptic drug therapy. In an epilepsy monitoring unit, patients can receive intravenous loading doses of anticonvulsive medication. Adverse effects can be identified promptly, and drug levels obtained easily. Ineffective drugs can be discontinued quickly.
Documenting Seizures
About 63% of all seizures were unrecognized by the patients in a study recorded in an epilepsy monitoring unit. Brief alterations of awareness occur in both absence and complex partial seizures. Patients with complex partial epilepsy are often amnestic for their seizures. Absence seizures may be so brief that the patient is unaware of them. A study using ambulatory EEG to evaluate absence seizures in pediatric patients found that most paroxysms of generalized spike and wave discharges are asymptomatic. Patients with mental retardation or other forms of encephalopathy may be unable to report seizures accurately.
This difficulty in identifying the occurrence of seizures impedes seizure diagnosis and assessment of treatment adequacy. Video EEG is very valuable at identifying seizures that are unrecognized or unreported by the patient. In such cases, video EEG can have a significant impact on clinical management. Video EEG monitoring may detect unrecognized seizures in patients who live alone or have minimal behavioral manifestations other than confusion. For example, complex partial status epilepticus may present as a prolonged confusional state. Video EEG monitoring may provide information about seizure frequency and may be more reliable with outpatient monitoring when patients engage in their usual activities in their natural environment.
Nocturnal or Sleep-Related Events
Certain diagnoses are difficult to confirm using the typical 30-minute outpatient EEG. The interictal epileptiform discharges of benign rolandic epilepsy, for example, are highly activated by sleep and may not always be achieved adequately in an EEG lab. Continuous spike and wave activity during slow-wave sleep is another entity that may demonstrate a relatively normal EEG during waking hours and a strikingly abnormal EEG during deep sleep. Because of its capacity to record an entire night of sleep, video EEG is invaluable in assessing these clinical situations.
The history may not differentiate clearly between sleep disorders (e.g., sleep apnea, narcolepsy, and REM sleep disorder) and epilepsy. Video EEG recording will help with the differential diagnosis.
Suspected Non-Epileptic Seizures
Non-epileptic seizures (also known as pseudoseizures or psychogenic seizures) are clinical events in which patients perceive altered movement, emotion, sensation, or experiences similar to those due to epilepsy but without an electrographic ictal correlate. They are surprisingly frequent, occurring in up to 20% of patients at epilepsy referral centers and in 5-20% of outpatient populations. Some patients have both non-epileptic seizures and epileptic seizures; coincident events occur in an estimated 10-60% of epilepsy patients. Video EEG is an essential tool in identifying patients who have non-epileptic paroxysmal events including non-epileptic seizures. Paroxysmal non-epileptic events can cause diagnostic confusion. Accurate diagnosis can be reached in the majority of cases using video EEG monitoring.
An Australian video EEG study in 666 pediatric patients showed 269 had epileptic events recorded, 285 had non-epileptic events and 112 had no events recorded. The major subgroups of non-epileptic events were: staring (34%), sleep phenomena—benign sleep myoclonus (15%), arousals (13%), motor tics (11%), and shuddering (7%).
Syncope Evaluation
Both syncope and seizures are very common clinical presentations and frequent reasons for neurology consultations. In some situations the differential diagnosis is difficult, especially with convulsive syncope and epileptic asystole (see Figures 1 and 2 on page 3). Video EEG is very useful in the differential diagnosis, especially if the events are captured on video EEG. A study of epileptiform abnormalities in ambulatory EEG found that only 1.5% (1 of 67) patients with syncope, near syncope, or episodic dizziness had an epileptiform abnormality.
Subclinical Electrographic Seizures
A Columbia University study in 570 critically ill patients showed that continuous EEG monitoring detected seizure activity in 19% of patients, and the seizures were almost always nonconvulsive. Coma, age less than 18 years, a history of epilepsy, and convulsive seizures prior to monitoring were risk factors for electrographic seizures. Comatose patients frequently required more than 24 hours of monitoring to detect the first electrographic seizure.
Presurgical Evaluation of Intractable Epilepsy
A significant number of patients have frequent drug-resistant disabling seizures. Epilepsy surgery may benefit these patients. In patients with intractable epilepsy, video EEG, both scalp and intracranial, has been used to localize seizure onset and to map vital brain function regions as part of pre-surgical evaluation.
Future Applications
Seizure anticipation methods are under development to identify EEG changes prior to seizure onset, allowing ongoing assessment of the probability of seizure occurrence. With further characterization of EEG changes in the pre-ictal state, future video EEG recording may be coupled with a seizure anticipation device, providing a time window for therapeutic intervention to prevent a seizure.
Figure 1. Seizure. Thirty seconds of EEG shown. Note EKG strip (bottom) and asystole with accompanying attenuation of the EEG.
Figure 2A: Seizure, with EEG spread out. Note the onset of rhythmic theta in the right temporal derivations, particularly in T2-T4 prior to the brady-arrhythmia, suggesting epileptic asystole.
Figure 2B: Seizure continued with EEG spread out. Note the continuation of a right temporal rhythm as asystole occurs.
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