Clinical Features, Video Head Impulse Test, and Subjective Visual Vertical of Acute and Symptom-Free Phases in Patients with Definite Vestibular Migraine

<b>Background/Objectives</b>: The most frequent neurologic cause of recurrent vertigo is vestibular migraine (VM). However, its diagnosis relies primarily on patients' histories, as specific diagnostic tests for VM are currently lacking. We aimed to examine and compare clinical features, vestibulo-ocular reflexes (VORs), and subjective visual vertical (SVV) between the ictal (IC) and inter-ictal (II) phases in VM patients. <b>Methods</b>: A repeated-measures study involved 31 patients with definite VM. Vestibular function was assessed using a video head impulse test (vHIT) to evaluate VOR results, and SVV testing to determine verticality perception. Otoneurological examination, including migraine-related disability, was noted. Analyses of repeated measures for numerical traits (SVV deviations, VOR, and clinical outcomes) were conducted using a linear mixed model (LMM), with phase, age, and sex as fixed effects and individual-specific random intercepts. Differences between the IC and II phases for dichotomous variables were analyzed using the χ2 or Fisher's exact test. <b>Results</b>: The LMM analysis revealed that SVV deviations were significantly higher ictally (IC-ly) (β = 0.678, <i>p</i> = 1.51 × 10^-6) than interictally (II-ly). VOR results remained normal across phases (<i>p</i> > 0.05), and refixation saccades did not differ significantly based on vHIT results (<i>p</i> > 0.05). Nausea (100% vs. 38.71%, <i>p</i> = 6.591 × 10^-8), photophobia (100% vs. 35.48%, <i>p</i> = 1.839 × 10^-8), and phonophobia (90.32% vs. 6.45%, <i>p</i> = 9.336 × 10^-12) were significantly more frequent IC-ly than II-ly. <b>Conclusions</b>: Our findings highlight phase-dependent alterations in spatial orientation, with increased SVV deviations IC-ly despite stable VOR. The significant differences in migraine-associated symptoms reinforce the dynamic nature of VM. These results emphasize the importance of timing in vestibular assessments and suggest that SVV testing during IC VM episodes may enhance diagnostic accuracy.