[Syncope of unclear origin--role of 2 diagnostic tests with high specificity].

We report the diagnostic evaluation of an elderly woman admitted with recurrent syncopes induced by head rotation. A cardiac origin was exclude by Holter ECG, echocardiography and carotid sinus compression. Angiography showed unilateral vertebral artery hypoplasia, suggesting the possibility of hemodynamic vertebrobasilar insufficiency. This origin, however, could be ruled out by monitoring of blood flow velocities in both posterior cerebral arteries with transcranial Doppler, which showed no alteration during syncope induced by head rotation. Detailed analysis of the course of the syncope recorded on videotape suggested a psychogenic event. Furthermore, the syncopes could be prevented with a "protective" placebo despite head rotation, and induced by a "provocative" placebo without head rotation while EEG monitoring showed normal brain activity. This finding underscored the suggestion of a psychogenic cause.