[Vestibulospinal reflexes in differentiating between organic and functional (psychogenic) causes of vertigo].

Recent investigations comparing the postural responses of normals and patients with bilateral peripheral vestibular deficit to a sudden backwards tilt of the support surface about the ankle joints have permitted an objective definition of the timing and amplitude of vestibulo-spinal reflex (VSR) EMG responses in ankle and neck muscles. The muscle contractions result in a sway stabilizing action correcting for induced body tilt, whose effect may be observed in ankle torque, and body and head angular acceleration records. The same techniques were used to monitor VSR responses of 10 patients with suspected simulated, aggravated, or psychogenic vertigo--vertigo of functional origin. Two cases, presented in detail, illustrate the identification of weak reflex responses for patients aggravating an organic VSR pathology during the Romberg test and the identification voluntarily controlled destabilizing responses for patients with a simulated or psychogenic vertigo. Recording the vertical vestibulo-ocular reflex in the same rotation plane as induced tilt is shown to provide valuable additional information on a possible peripheral vestibular pathology. It is concluded that VSR responses time-locked to a vestibular stimulus provide an improved means of identifying a functionally based vertigo.