Changes in the vestibulo-ocular reflex after plugging of the semicircular canals

Lateral semicircular canal plugging in severe Ménière's disease: a clinical prospective study about 28 patients

OBJECTIVE

To evaluate the safety and efficiency of the plugging of the lateral semicircular canal to control vertigo in severe Ménière's disease (MD).

STUDY DESIGN

Prospective follow-up study.

SETTING

University hospital.

PATIENTS

Twenty-eight patients with MD with refractory vertigo and severe disability (functional scale 5 or 6).

INTERVENTIONS

Lateral canal plugging was performed in pathological ear for each patient.

MAIN OUTCOME MEASURES

The evaluation of therapy followed the guidelines for diagnosis and evaluation of therapy in MD (1995). Hearing, frequency of vertigo, and functional disability were assessed in the early follow-up (6 mo) for all the patients and in the late follow-up (2 yr) for 16 patients. In addition, the canal paresis was evaluated by caloric test.

RESULTS

No vital complication occurred. The hearing was preserved in 82% of cases. Lateral canal plugging induced in all cases a canal paresis that was persistent after 2 years. After 2 years (n = 16), the control of vertigo was complete or substantial in 75% of cases (A1, restoration of a normal life: 62.5%; B2, no functional restriction: 12.5%).

CONCLUSION

Lateral canal plugging is a safe procedure that induces a canal paresis and allows a good control of vertigo. In view of these results, the lateral canal plugging should be a therapeutic option for controlling rotatory vertigo in severe MD.

Partial behavioral compensation is revealed in balance tasked mutant mice lacking otoconia

We describe for the first time behavioral tests which show that mammals with congenital absence of otoconia can learn a motor task that normally relies on gravity perception. The mouse mutation tilted (tlt) occurs in the otopetrin 1 gene (Otop1(tlt/tlt)) and eliminates an essential component necessary for the formation of otoconia. Our data show that even in the absence of otoconia, tlt mutant mice, like normal mice, learn to cross a bar suspended between two boxes and, with practice, improve their speed of crossing. Despite this learned compensatory skills, tlt mutant mice show balance impairments, such as falling from the bar, not observed in wild type (WT) or heterozygous (het) Otop1(+/)(tlt) littermates. The tlt mutant mice also use their tail as additional support, a behavior that is rarely exhibited in the control littermates. Interestingly, the Otop1(+/)(tlt) heterozygous littermates show in many aspects an intermediate phenotype between wild type and tlt mutant mice, suggestive of a gene dosage effect. Overall, these data support the notion that mammals can use other otic and extraotic receptors such as semicircular canals and limb proprioreceptors, respectively, to compensate for the absence of otoconia-mediated gravity perception in a balance task.

Torsional and horizontal vestibular ocular reflex adaptation: three-dimensional eye movement analysis

This study used visual-vestibular conflict to effect short-term torsional and horizontal adaptation of the vestibulo-ocular reflex (VOR). Seven normal subjects underwent sinusoidal whole-body rotation about the earth-vertical axis for 40 min (+/- 37 degrees/s, 0.3 Hz) while viewing a stationary radial pattern fixed to the chair (x0 viewing). During adaptation and testing in darkness, the head was pitched either up or down 35 degrees to excite both the horizontal and torsional VOR. The eyes were kept close to zero orbital elevation. Eye movements were recorded with a dual search coil in a three-field magnetic system. VOR gain was determined by averaging peak eye velocity from ten cycles of chair oscillation in complete darkness. The gain of the angular horizontal VOR (response to rotation about the head rostral-caudal axis) was significantly reduced after training in both head orientations. Angular torsional VOR gain (head rotation about the naso-occipital axis) was reduced in both head orientations, but this reached statistical significance only in the head down position. These results suggest that torsional and horizontal VOR gain adaptation, even when elicited together, may be subject to different influences depending upon head orientation. Differences between head up and down could be due to the relatively greater contribution of the horizontal semicircular canals with nose-down pitch. Alternatively, different VOR-adaptation processes could depend on the usual association of the head down posture to near viewing, in which case the torsional VOR is relatively suppressed.