Caloric-vHIT Dissociation in Vestibular Migraine: An Observational, Retrospective Case Series Study.

Background: Caloric-vHIT (CalHiT) dissociation has been considered highly characteristic of Ménière's disease (MD), but its occurrence in vestibular migraine (VM) remains incompletely characterized. Objective: The primary aim was to characterize, through detailed longitudinal analysis, the clinical and mechanistic heterogeneity underlying caloric-vHIT dissociation in seven patients with definite VM in a retrospective cohort. Study design: Observational, retrospective case series. Methods: From a standardized vestibular cohort of 100 consecutive patients with definite MD or VM evaluated between 2015 and 2018, seven patients with definite VM who exhibited caloric-vHIT dissociation were identified and followed up for approximately seven years. The frequency of dissociation patterns within the source cohort was recorded to contextualize case selection, and each case was characterized descriptively as follows: Patterns were classified as CalHiT-0 (CP < 22%, vHIT ≥ 0.80), CalHiT-A (CP ≥ 22%, vHIT ≥ 0.80), CalHiT-B (CP < 22%, vHIT < 0.80), and CalHiT-C (CP ≥ 22%, vHIT < 0.80). Results: At the cohort level, A-pattern dissociation occurred in 17.5% of patients with VM (7/40) and 56.7% of patients with MD (34/60), while B-pattern dissociation was rare (MD: 2/60, 3.3%; VM: 1/40, 2.5%). One patient with CalHiT-A VM was lost to follow-up and excluded from the longitudinal analysis. At the case level, the seven cases (six CalHiT-A and one CalHiT-B) suggested mechanistic heterogeneity, including compensated peripheral hypofunction, familial vulnerability, traumatic injury, and potential central modulation. VM was distinguished by the absence of fluctuating auditory symptoms, absence of progressive hearing loss characteristic of MD, and DHI-measured disability comparable to that of MD despite substantially lower objective vestibular deficits. No VM case with confirmed follow-up evolved toward MD. Conclusions: Caloric-vHIT dissociation occurred in approximately one-sixth of patients with definite VM and should not be regarded as a stand-alone sign of endolymphatic hydrops. The clinical heterogeneity across cases suggests that several mechanisms other than hydrops may produce a comparable pattern. These observations could support future studies exploring whether a distinct VM phenotype defined by this dissociation can be established and favor interpreting the dissociation alongside the auditory and longitudinal profiles rather than in isolation.