Neurologic Testing of Low Yield in Syncope Evaluation
Abstract & Commentary
Source: Pires LA, et al. Arch Intern Med. 2001;161:1889-1895.
It is well appreciated that the diagnosis of acute syncope is best guided by a detailed history and physical examination. The addition of diagnostic tests such as CT scanning, EEG, or cardiac testing may reduce but not eliminate the considerable diagnostic uncertainty involved with syncope evaluations. As Pires and colleagues observe, neurologic tests may be of particularly dubious value unless they are appropriately tailored to the clinical picture.
Pires et al retrospectively reviewed 649 patients admitted to 2 community hospitals with a primary diagnosis of syncope. Patients were studied from 2 time periods: 1994 (451 patients) and 1998 (198 patients). Results did not substantially differ between the 2 hospitals or time periods.
CT or EEG provided a diagnosis in a small subset (11 patients) among whom clinical history was consistent with seizure (n = 14) or stroke (n = 20). CT or EEG was of no use in diagnosis among patients with presentations inconsistent with a CNS event. CT or EEG was performed frequently in almost half the study patients, giving each an overall diagnostic yield of only 2%. Carotid dopplers, performed in 185 patients, and MRI, done in only 10 patients, yielded no significant diagnostic results.
The highest yield test, postural blood pressure testing, was used in a minority of patients, 176 (27%), but successfully explained syncope in 52 of these, a 30% diagnostic yield. Head-up tilt-table testing and electrophysiology studies also had high yields, in the range of about 20%, but were used in even fewer patients.
Other forms of cardiac testing were more widely applied and were not generally successful. Continuous telemetry (performed in all 649 patients), holter monitoring (performed in 193), or echocardiography (performed in 277) explained syncope in only 7, 6, and 3 cases, respectively. These tests thus showed a diagnostic yield in the range of 1-3%, comparable to that of CT/EEG.
Patients undergoing cardiac or neurologic consultation were more likely to have diagnoses falling into these categories than patients seen only by primary care physicians. Thirteen of 92 patients seen by a neurologist were determined to have a neurologic cause for syncope compared with 2/181 seen by a cardiologist or 7/225 seen by primary care providers. Conversely, a cardiac etiology of syncope was identified in 31 patients seen by a cardiologist, compared with 13 or 3 patients seen by a neurologist or primary care physician.
Overall, a diagnosis for syncope was identified in 329 patients. The most common etiologies were a drug reaction or metabolic cause (including orthostatic hypotension, n = 161) or a vasovagal spell (n = 71).
Unless stroke or seizure is likely based on clinical grounds, CT and EEG are of little use in syncope evaluation. The most effective "test" proves to be postural blood pressure testing, which is merely an extension of a thorough physical examination. This clearly represents a victory for basic clinical medicine over more expensive modern technologies.
As Pires et al point out, these results may be reinterpreted based on the referral bias. Neurologists may see a subset of the overall population with syncope among whom CNS tests are more justified. On the other hand, only 13 of these patients had a neurological diagnosis, leaving the majority of the 92 cases seen by neurologists in the unknown or cardiac categories.
It is not surprising that carotid doppler ultrasound was of no diagnostic yield in this study, as carotid stenosis, particularly if unilateral, does not typically present in this manner. The study, however, does not address vertebrobasilar disease, which may cause syncope and would warrant either transcranial doppler or MRA evaluation in selected cases. —Alan Z. Segal
Segal, MD, Assistant Professor, Department of Neurology, Weill-Cornell Medical College, and Attending Neurologist, New York Presbyterian Hospital, is Assistant Editor of Neurology Alert.