Individuals suffering a transient loss of consciousness usually fall into two broad conditions: syncope and seizure disorders. Syncope generally results from the lack of blood supply and resultant hypoxia to the brain from a number of causes, including vasovagal events, bradycardia, tachycardia, malignant cardiac arrhythmias, hypovolemia, and GI blood loss. A seizure is usually the result of intracranial pathology such as epilepsy, other brain pathology, metabolic abnormalities (glucose, sodium, magnesium, calcium), the result of a toxin, and drug or alcohol withdrawal.
These causes of transient loss of consciousness are generally initially considered and then ultimately deciphered by the emergency physician based on history and other clinical parameters. The individual with previously diagnosed epilepsy who has missed his medication and suffers a seizure presents a seemingly relatively simple approach in the ED. It turns out, however, that this is not always so straightforward. Those who faint in church on a hot day are also usually an uncomplicated evaluation. The EP may not always know what happened in the field and has to rely on past history in medical records, a report from bystanders, or a best guess.
The ED approach to syncope and seizures is often initially the same but ultimately different. The next few columns will attempt to differentiate a seizure from a syncopal episode and discuss the ED approach to ferret out the actual cause.
Misdiagnosis of Epilepsy: Many Seizure-Like Attacks Have a Cardiovascular Cause
Zaidi A, Clough P, et al.
J Am Coll Cardiol
This report from a cardiology center and a neurology center raises some vitally important points that may not be obvious, known, or well appreciated by most emergency clinicians. It notes an increasing recognition of the misdiagnosis of epilepsy. These authors state that about 20 percent of patients undergoing long-term follow-up in a specialized epilepsy clinic actually do not have epilepsy. They refer to a prior study where a clinic specializing in epilepsy found that it had been misdiagnosed in 26 percent of patients taking antiepileptic medications. (QJM 1999;92:15.)
About 23 percent of patients with a primary diagnosis of epilepsy were also misdiagnosed in a community-based study, and the diagnosis of epilepsy was unclear in another 12 percent. (Pacing Clin Electrophysiol 1989;12[1 Pt 1]:117.) Cardiovascular convulsive syncope was the most commonly misdiagnosed condition in both reports.
The authors note that many cardiovascular disorders may cause blackouts that are associated with abnormal motor movements secondary to cerebral hypoxia, activity that can be misinterpreted by a bystander as a seizure. It is not uncommon for patients with vasovagal syncope or carotid sinus syncope to have brief seizure-like activity following an episode. This is termed convulsive syncope. These episodes are identical to epileptic seizures, accounting for the incorrect diagnosis. The patient diagnosed with epilepsy has many other consequences, such as driving, occupation, and insurance rates, in addition to the inappropriate use of expensive and potentially harmful anticonvulsant drugs.
The clinical evidence gleaned from a patient in the ED may not be sufficient to differentiate between seizure and syncope. The labs, physical exam, and ECG are often not helpful. Probably the only specific and sensitive test to clinch the diagnosis of epilepsy is extended video telemetry monitoring with an EEG recording. This test is not widely available and is often not used in patients with presumed seizure attacks. The authors of this article report on the initial results of a multidisciplinary approach with the investigation of convulsive blackouts using data from simple provocative tests rather than the clinical history alone to confirm the underlying diagnosis.
The authors studied 74 patients with recurrent seizure-like episodes that had been previously diagnosed as epilepsy on clinical grounds and had been referred to a neurology center. Antiepileptic drugs had been prescribed. Almost 40 percent of the patients continued having loss of consciousness and asynchronous muscular activity despite adequate doses of anticonvulsants, amazingly up to three medications in at least seven patients. A nonseizure EEG obtained in 66 patients was normal in 53 and nonspecific in 13. A CT or MRI of the brain showed no abnormality. The 12-lead ECG taken on only 10 patients was normal.
Each patient in this study had a head-up tilt table test and carotid massage. Continuous ECG and blood pressure monitoring were recorded throughout the study, and an eight-channel EEG was performed simultaneously. Carotid sinus massage was performed for five seconds on each side of the neck in a supine position with carotid sinus hypersensitivity diagnosed as a pause of greater than three seconds. Some patients also had an outpatient EEG recording.
The resting 12-lead ECG was normal in every patient, but 25 percent of patients diagnosed with epilepsy experienced their usual symptoms during their head-up tilt table test with profound hypotension and bradycardia, consistent with vasovagal syncope. Sixty-three percent had marked abnormal motor movements that included initial tonic muscular activity and extension and flexion of the arms. Asynchronous multifocal muscle jerking lasted up to 15 seconds. The degree of bradycardia on the ECG correlated with the symptoms. There was a significant ECG pause (asystole) during carotid sinus massage on 10 percent of the patients, who subsequently underwent permanent pacemaker insertion. Overall, an alternative diagnosis to epilepsy was found in 42 percent of patients. Those with an alternative diagnosis were seizure-free after about 10 months.
The authors pointed out that convulsive syncope is not uncommon. Previous studies have shown that up to 12 percent of blood donors experiencing vasovagal events had accompanying seizure-like activity. Muscular jerking was seen in 90 percent of those where syncope could be induced by hyperventilation or orthostatic changes. The arrest of cerebral circulation has been well known to cause myoclonic activity mimicking a seizure.
These authors said head-up tilt table testing clearly has a role in identifying cases of convulsive vasovagal syncope that could be misdiagnosed as epilepsy. It is well known that it is difficult to confirm that convulsive syncope is the result of a cardiac arrhythmia because the yield of resting and outpatient ECGs is rather low. The use of long-term implantable loop cardiac recorders is a major advance in the investigation of arrhythmic syncope. A positive cardiac diagnosis was obtained in almost 60 percent of patients who had unexplained syncope in one study.
The authors concluded that there is significant difficulty in diagnosing syncope versus seizures, particularly in differentiating the two. Readers are encouraged to consider cardiac issues in any case of seizure-like activity with a loss of consciousness.
Comment: I found this article to be quite enlightening. I thought I knew the basics of ED thinking when approaching a patient with transient loss of consciousness but apparently not. Even if the patient tells you that he has epilepsy and is on anticonvulsant medication, he may actually have a cardiac etiology that will escape many clinicians. Few clinicians would doubt the previously made diagnosis, especially those with minimal evaluation available in the ED.
It's difficult to believe that as many as 20-30 percent of epileptics have been misdiagnosed and that many are put on long-term medications, often without any effect. This error should especially be considered in those with recurrent seizures despite the documented use of anticonvulsants. Many of these patients have cardiovascular syncope that is associated with abnormal movements from cerebral hypoxia, muscular activity that is difficult to differentiate from epilepsy on clinical grounds. This was a study of very selective patients and exactly how the seizure was diagnosed before evaluation was not elucidated, but these authors found that almost 42 percent of patients initially thought to have epilepsy had an incorrect diagnosis. The diagnosis was cleared up with a simple tilt table test and prolonged outpatient ECG monitoring.
Most clinicians have seen patients have short classic seizure-like activity when they faint after a blood draw or a significant orthostatic challenge. EMS and laypeople clearly would call such an event a seizure. Importantly, the patient with chest pain and a seizure should first conjure up the diagnosis of ventricular fibrillation.
The emergency clinician has little availability of a tilt table test or outpatient ECG monitoring for those with a transient loss of consciousness. As noted in this case, many times the resting ECG is normal. One could do a simple orthostatic test in the ED, but it's not quite as sophisticated as a tilt table analysis.
Most patients with an undiagnosed transient loss of consciousness are referred to a neurologist or cardiologist. It is often the emergency physician who makes that call, and a patient may be put on anticonvulsants by his private physician after a few basic tests have been performed that do not elicit the exact etiology. It is quite variable exactly how the outpatient physician works up such a patient, and most do not receive the testing performed by this study. An alternate diagnosis to epilepsy should be considered in patients who have this diagnosis and yet continue to seize despite therapeutic doses of medications. Think twice before adding another anticonvulsant. It would certainly be premature for the emergency physician to make a new diagnosis of epilepsy or an occult arrhythmia in patients with normal ED testing and a clinical story that cannot even accurately differentiate syncope from a true seizure.
It is important to note that less than half of the patients with epilepsy have an identifiable cause. A normal EEG does not rule out epilepsy. One ECG in the ED does not define a cardiac workup, and even a short-term Holter monitor may not pick up torsades, bradycardia, or heart block as the cause of convulsive syncope. Physical findings, such as incontinence, have low diagnostic sensitivity. I guess it's time for me to rethink my ED understanding of transient loss of consciousness and the approach to the patient with seizures despite the use of anticonvulsants.
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