Functional Dissociation Between Cervical VEMP and Posterior Canal vHIT in 1770 Unselected Ears.

OBJECTIVE: Cervical vestibular evoked myogenic potentials (cVEMP) and posterior canal video head impulse testing (PC-vHIT) are conventionally treated as measures of one inferior vestibular unit. We quantified how often they disagree, and whether this varies with age. METHODS: Retrospective cross-sectional analysis of a single-center vestibular registry. All records with 500 Hz cVEMP amplitudes and posterior canal vHIT gains for both ears were extracted without diagnostic or age filtering. Per ear, cVEMP was abnormal if the response was absent, or if the absolute interaural amplitude difference was ≥ 40% and that ear had the smaller amplitude; bilaterally absent responses were classified abnormal bilaterally and analyzed separately. PC-vHIT abnormality was gain < 0.7. Agreement was quantified with Cohen's κ, using patient-clustered bootstrapping and generalized estimating equations. RESULTS: A total of 1770 ears from 885 examinations in 868 patients were analyzed (mean age 53.9 years). Of 1027 ears abnormal on at least one test, 747 (72.7%) were abnormal on only one; 280 (27.3%) were concordantly abnormal. Agreement was minimal (κ = 0.097, 95% CI 0.047-0.150). Both abnormality rates rose with age, yet κ was flat across strata (0.073, 0.056, 0.040, and -0.012 for < 40, 40-59, 60-69, and ≥ 70 years), so the age-related fall in raw discordance reflects rising prevalence, not a changed relationship. That rise was almost entirely bilateral cVEMP absence. CONCLUSION: cVEMP and PC-vHIT disagree in roughly three-quarters of affected ears, with chance-corrected agreement near zero at every age. They are better read as two reflex loops sharing a peripheral segment, not interchangeable measures of one entity.