Reviewed and updated by Valerie Dziados, MSN, CRNP, ANP-BC, AGACNP-BC: March 20, 2024

Achieving the correct final diagnosis with the presenting symptom of transient loss of consciousness can challenge even the most seasoned clinician. Syncope and epileptic seizures reign high on the list of differential diagnoses, followed by narcolepsy, cataplexy, pseudoseizures, and pseudosyncope (Sheldon, 2015). Distinguishing between these top two contenders can be difficult and often the investigation is inconclusive or incorrect.

What Is the Difference Between Syncope and Seizures?

Research suggests that between 20-40% of patients diagnosed with epilepsy have been misdiagnosed, and syncope is the most common misdiagnosis in epilepsy (Hackethal, 2017). Let’s take a closer look into this medical diagnosis conundrum.

Symptoms and Causes of Syncope

Syncope is defined as a symptom that presents with an abrupt, transient, complete loss of consciousness, associated with inability to maintain postural tone, with rapid and spontaneous recovery, and that is caused by cerebral hypoperfusion. Studies of syncope report prevalence rates as high as 41%, with recurrent syncope occurring in 13.5%, and the prevalence of syncope as a presenting symptom to the ED ranged from 0.8% to 2.4% (Shen et al., 2017). The most common causes of syncope include reflex syncope (blood/injury exposure), orthostatic syncope, cardiac arrhythmias, and structural cardiopulmonary disease (Benditt, 2024). Often syncope is preceded by a prodrome or period of presyncope that may include a constellation of symptoms including lightheadedness, feeling warm or cold, diaphoresis, palpitations, nausea/abdominal discomfort, visual blurring, pallor, or changes in hearing (Benditt, 2024).

Symptoms and Causes of Seizures

Seizures fall into two categories: epileptic and non-epileptic.

Epileptic seizures occur spontaneously or unprovoked and are recurrent. They are further classified as generalized tonic-clonic seizure and the more common, partial complex seizure (Sheldon, 2015). Causes of epileptic seizures include brain injury, stroke, brain tumors, and neurological disorders. Diagnosis is made by abnormal brain activity on an electroencephalogram (EEG).

Non-epileptic seizure causes can include fever, infection, electrolyte imbalance, drug/alcohol withdrawal, psychological conditions, and hypoglycemia. You will expect to find normal brain wave activity on EEG testing in a patient with a non-epileptic seizure.

What Is Convulsive Syncope?

Many syncopal events include loss of consciousness as the only symptom. The diagnostic problem occurs when a patient with syncope also has myoclonic jerks or convulsions. These events are sometimes referred to as seizure-like syncope or convulsive syncope. Myoclonic jerks and tonic spasms are the most misleading symptoms in the differential diagnosis between syncope and seizures (Bergfeldt, 2003). The underlying pathophysiology of convulsive syncope is as follows: the cardiac syncope causes a variable amount of hemodynamic instability resulting in cerebral hypoperfusion, which triggers the medullary reticular formation and results in myoclonic activity that mimics seizure activity (Patel and Cohen, 2013).

Diagnosing Syncope versus Seizures

The gold standard to differentiate between the two would require videotelemetry with simultaneous EEG and electrocardiographic (ECG) recording with scalp and chest electrodes – a clinical scenario that is rarely fulfilled (Bergfeldt, 2003). One of the most important clues usually comes from an observant bystander who witnesses the event and is able to report if the person went limp then convulsed (syncope) or if the episode began with convulsions (seizure). Be alert for other clues, as well.

Identifiable triggers are associated with syncope, and seizures tend to have a longer duration than syncope and are followed by postictal confusion and significant fatigue, although brief periods of confusion have been reported with convulsive syncope. Other common features of convulsive syncope that are not common in seizures include a period of presyncope with prodrome, pallor, duration less than one minute, and fixed or upward eye deviation. Conversely, common features of a seizure, that are not common in syncope, can include tongue biting, prodromal cry, incontinence, duration often a few minutes, and lateral eye deviation (Sheldon, 2015). Accurate diagnosis is often challenged by the patient’s amnesia of the events, lack of bystander presence/account, and discordance among clinician opinions (McKeon, Vaughan, and Delanty, 2006).

Evaluating Patients for Seizures versus Syncope

Evaluation of a patient that presents with transient loss of consciousness can be extensive and often include cardiology and neurology consultations. All patients must have a comprehensive history and physical examination.

The detailed history must include:

• Detailed past medical history
• Number, frequency, and duration of episodes
• Time of onset
• Body position when the event occurred
• Provocative factors or associated symptoms preceding the event
• Symptoms following the event
• Witness account, if available
• Medications
• Family history

The physical exam must include:

• Pulse and blood pressure measurements while the patient is lying, sitting, and standing to assess for orthostatic hypotension
• Blood pressure in each arm; inequality suggests aortic dissection or aortic coarctation
• Respiration rate to assess for hyperventilation as seen with pulmonary and/or psychiatric causes
• Careful auscultation of heart sounds to assess for cardiac murmurs
• Consider careful carotid massage in an older patient
• Neurological exam

Recommended Testing

Initial evaluation should also include ECG, echocardiogram, and basic laboratory testing to exclude anemia, infection, electrolyte imbalances, or renal and liver dysfunction.

The ECG is a powerful tool in the setting of evaluation of a patient with transient loss of consciousness. The ECG can help with the assessment for arrhythmias (sinus bradycardia, sinus pauses, atrioventricular heart blocks, ventricular tachycardia, bundle branch blocks), intraventricular conduction delays, pre-excited QRS complexes, left ventricular hypertrophy, and pacemaker or implantable cardioverter-defibrillator malfunction, as well as others.

An echocardiogram assesses for structural heart disease including left ventricular dysfunction, hypertrophic cardiomyopathy, significant aortic stenosis, intracardiac tumors, and right ventricular enlargement (suggestive of pulmonary embolism). This initial evaluation yields a relative certain diagnosis approximately 50% of the time (Benditt, 2024).

Based on the yield from the initial investigation, further testing may be warranted depending on results and clinical suspicion. When the suspicion of epilepsy is high with the first unprovoked seizure or focal neurologic deficits, a 30-minute interictal EEG and neuroimaging including CT or MRI.

Ambulatory cardiac ECG monitoring is warranted when there is suspicion that a cardiac arrhythmia may be the cause of syncope. There are three choices for ECG monitoring, including continuous ambulatory ECG (Holter) monitoring and patch monitoring, event monitoring and mobile cardiac outpatient telemetry (MCOT) monitoring, and insertable cardiac monitors. While exercise stress testing tends to have a low diagnostic yield in patients with syncope, it can be helpful in those patients where the symptoms occurred with maximum exercise. Tilt testing is controversial and generally not performed (Benditt, 2024).

Carotid sinus massage can be considered to uncover carotid sinus syndrome, that mostly affects males older than 60 years of age or patients with prior head and neck surgery. It should be performed by an experienced clinician and is not advisable in patients with history of transient ischemic attack or stroke within the past three months and in patients with carotid bruits (Benditt, 2024).

When a patient presents with transient loss of consciousness, identifying the accurate underlying diagnosis can be daunting. This is a manageable task however, by first documenting an excellent history and physical, then performing the above standard tests, and finally, collaborating with your cardiology and neurology colleagues.

Syncope versus Seizure References

Benditt, D. (2024). Syncope in adults: Clinical manifestations and initial diagnostic evaluation. UpToDate. www.uptodate.com/contents/syncope-in-adults-clinical-manifestations-and-diagnostic-evaluation

Benditt, D. (2024). Syncope in adults: risk assessment and additional diagnostic evaluation. UpToDate. www.uptodate.com/contents/syncope-in-adults-risk-assessment-and-additional-diagnostic-evaluation

Bergfeldt L. (2003). Differential diagnosis of cardiogenic syncope and seizure disorders. Heart (British Cardiac Society), 89(3), 353–358. https://doi.org/10.1136/heart.89.3.353

Hackethal, V. (2017). Epilepsy, syncope, or both? NeurologyLive.  https://www.neurologylive.com/view/epilepsy-syncope-or-both

McKeon, A., Vaughan, C., & Delanty, N. (2006). Seizure versus syncope. The Lancet. Neurology, 5(2), 171–180. https://doi.org/10.1016/S1474-4422(06)70350-7

Patel, D.P. & Cohen, T.J. (2013). Cardiac syncope versus seizure: The value of the EP consult. EP Lab Digest, 13(2). https://www.hmpgloballearningnetwork.com/site/eplab/feature-story/cardiac-syncope-versus-seizure-value-ep-consult

Sheldon R. (2015). How to Differentiate Syncope from Seizure. Cardiology clinics, 33(3), 377–385. https://doi.org/10.1016/j.ccl.2015.04.006

Shen, W. K., Sheldon, R. S., Benditt, D. G., Cohen, M. I., Forman, D. E., Goldberger, Z. D., Grubb, B. P., Hamdan, M. H., Krahn, A. D., Link, M. S., Olshansky, B., Raj, S. R., Sandhu, R. K., Sorajja, D., Sun, B. C., & Yancy, C. W. (2017). 2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients With Syncope: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. Circulation, 136(5), e60–e122. https://doi.org/10.1161/CIR.0000000000000499

 

 

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