Functional head impulse test and video head impulse test in interictal Ménière's disease and inferior vestibular neuritis: a preliminary comparative study.

Background and objective: In interictal Ménière's disease (MD), a caloric-vHIT dissociation is well established: caloric testing reveals vestibular hypofunction, yet video head impulse test (vHIT) gains in the lateral canal are preserved. Whether this preservation corresponds to preserved functional gaze stabilization remains unknown. This preliminary, exploratory study compared affected and unaffected ear responses of dynamic visual acuity (DVA), functional head impulse test (FHIT), and vHIT in interictal MD, and evaluated the clinical value of each measure. Methods: Eleven interictal MD patients (10 female, 1 male; mean age 61.6 ± 16.7 years) and 12 inferior vestibular neuritis (IVN) patients (6 female, 6 male; mean age 61.5 ± 9.9 years) were enrolled. IVN was defined by reduced posterior canal vHIT gain (<0.7) or absent cVEMP on the affected side. All tests were performed during the interictal phase (≥48 h after the last episode). Six-canal FHIT (correct answer rate, CA%), six-canal vHIT, and DVA were measured. Lesion-side versus intact-side comparisons used the Wilcoxon signed-rank test. Results: In MD, lesion-side FHIT-H CA% was significantly lower than intact-side (53.9 ± 33.5% vs. 77.3 ± 26.5%; Conclusion: MD and IVN showed contrasting patterns: MD exhibited selective lesion-side FHIT-H reduction with preserved vHIT, whereas IVN showed selective posterior canal vHIT reduction with normal FHIT-H laterality. These findings suggest that FHIT may reflect endolymphatic hydrops-related functional vestibular changes distinct from the structural nerve lesions characteristic of IVN. FHIT may be a useful adjunct for detecting functional vestibular asymmetry in interictal MD; these findings are hypothesis-generating and require replication in larger prospective cohorts.