[Postural stabilization after otolithic repositioning for posterior semicircular canal canalization].

Today the canal/cupulolithiasic pathogenesis of benign paroxysmal positional vertigo (BPPV) appears well defined; what is less clear is the origin of the postural "instability" often associated with rotatory vertigo. This form is less marked but still resists all know treatments. The purpose of the present study was to determine the actual postural arrangement of subjects suffering from canalolithiasis (CL) of the posterior semicircular canal (PSC) both before and after the positioning maneuver. In this case a personal method of spectral frequency analysis was used in an attempt to clarify the origin of the residual "instability" following otolithic repositioning. Static posturographic testing was performed on 20 patients with CL of the PSC and another 20 normal subjects of comparable age. In the present study the repositioning maneuver leads to a reduction in latero-lateral oscillation without any anterior-posterior variation. Such stabilization covers all the frequencies if a visual input is also present while it is limited to the lower frequencies when the visual content is lacking. In fact, in the latter case the subject maintains his posture using only vestibular and proprioceptive input. On the other hand, the anterior-posterior oscillations increase in all frequency ranges and this increase remains essentially unchanged after the repositioning maneuver. The authors feel that the anterior-posterior destabilization seen in CL of the PSC may stem from a proprioceptive-macular alteration linked to otolitic detachment rather than abnormal ampullar stimulation. The persistence and residual postural alterations found could, therefore, explain the persistent sense of instability that CL patients often complain of, even after the maneuvers which have encountered such success in controlling BPPV.