Decreased postural adaptation in patients with phobic postural vertigo--an effect of an "anxious" control of posture?

Postural adaptability and responses elicited by vibratory stimulation to the calf muscles recorded on a force platform with eyes open or closed were analyzed in 39 patients suffering from Postural Phobic Vertigo (PPV) (17 men and 22 women, mean age 49 years) and 24 healthy subjects (14 men, 10 women, mean age 38 years). The vibration induced increased body sway in both groups, but the adaptation pattern differed significantly. With eyes open the PPV patients decreased their induced body sway over time (-32%, p<0.01), which the controls did not. With eyes closed the PPV patients reduced their induced body sway over time to a much lesser extent than the controls (PPV: -28%, p<0.05, controls: -57%, p<0.001). These new findings show that PPV patients adapt to proprioceptive perturbation to a lesser extent than normal subjects and that PPV patients do not use visual information as efficiently to modulate postural control. The results support the hypothesis that a cognitive set of posture, an "anxious control", may underlie the symptoms of PPV, i.e. an increased readiness to react to any perturbation or deviation.