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Make the Diagnosis: Did This Patient With Transient Loss of Consciousness Have Syncope or Seizure?

Prior Probability of Syncope or Seizure in Patients With Transient Loss of Consciousness

The most common causes of transient loss of consciousness with spontaneous recovery are cardiac syncope, reflex syncope, and orthostatic hypotension. Cardiac syncope refers to syncope caused by marked reduction in cardiac output caused by cardiopulmonary disease. Reflex syncope is a centrally mediated decrease in heart rate, systemic vascular resistance, or both that is most typically brought on by increased vagal tone (vasovagal syncope). Orthostatic hypotension occurs with a change in posture and results from decreased intravascular volume or systemic vascular resistance. Among primary care or emergency department patients with transient loss of consciousness, the prevalence of cardiac syncope is 5% to 21%; vasovagal syncope, 21% to 48%; and orthostatic hypotension, 4% to 24%. Many patients have unexplained syncope (17% to 37%).

A much smaller number of patients with transient loss of consciousness will have experienced a seizure (prevalence of seizures in the general population is 0.3% to 1.7%). Nonsyncopal syndromes such as psychogenic nonepileptiform events are more common than actual seizures (8% to 20% of patients with transient loss of consciousness).

Population Among Whom Syncope or Seizure Should Be Considered

Syncope or seizure should be considered in any patient with transient loss of consciousness. An accurate witness report of seizure-like activity facilitates the diagnosis of seizure. Based on the importance of the condition and prevalence of the causes for transient loss of consciousness, a stepwise diagnostic approach is recommended (Figure 108-2).1,2

Assessing the Likelihood That the Patient Had Cardiac vs Noncardiac Syncope

Among patients with transient syncope, initial concerns should be directed to the evaluation for cardiac syncope vs noncardiac syncope. Most individual findings do not have sufficient sensitivity or specificity to confirm a diagnosis of cardiac syncope. Therefore, expert opinion from guidelines (Figure 108-2) that emphasize combinations of findings including the results of an electrocardiogram are recommended. The Evaluation of Guidelines in Syncope Study (EGSYS) scale (which is based on 6 clinical variables with a range of −2 to 12) may be helpful. Higher scores indicate higher likelihood of cardiac syncope. An EGSYS score less than 3 may indicate lower likelihood of cardiac syncope (Table 108-1 and Table 108-2).3,4

Table 108-1.Useful Findings for Identifying Cardiac Syncope

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