Caloric canal paresis thresholds in relation to vHIT-defined acute unilateral vestibular dysfunction: a retrospective analysis.

Background: Caloric testing and the video head impulse test (vHIT) assess vestibular function at different frequency ranges and provide complementary information in patients with acute vertigo. Although a canal paresis (CP) threshold of 25% is commonly used to define caloric abnormality, interpreting CP values in relation to vHIT-defined unilateral high-frequency vestibular dysfunction remains clinically challenging. Objective: We evaluated how conventional and alternative caloric CP thresholds align with vHIT-defined acute unilateral vestibular dysfunction and sought an interpretive CP threshold best corresponding to vHIT-defined findings. Methods: This retrospective analysis included patients presenting with acute vertigo within 72 h of symptom onset who underwent both caloric testing and vHIT at a tertiary referral center. Patients with clinically suspected benign paroxysmal positional vertigo, Ménière's disease, vestibular migraine, sudden sensorineural hearing loss or labyrinthitis with acute auditory symptoms, central vestibular disorders, bilateral vestibulopathy, or bilateral caloric weakness were excluded. vHIT-defined unilateral dysfunction was based on compatible clinical features and abnormal horizontal-canal vHIT findings indicating unilateral high-frequency vestibulo-ocular reflex dysfunction. Receiver operating characteristic (ROC) analysis examined how caloric CP values corresponded to this classification. Results: Of 1,634 eligible patients, 145 met criteria for vHIT-defined unilateral dysfunction. The symptomatic vHIT-normal comparison group comprised 1,489 patients without a final diagnosis of definite peripheral or central vestibular disease, although some had isolated caloric abnormalities. The conventional 25% CP threshold showed high sensitivity for the vHIT-based classification but classified a larger number of symptomatic vHIT-normal patients as CP abnormal. ROC analysis identified an approximately 30% CP threshold (Youden's index) with sensitivity 0.945 and specificity 0.867. This threshold reduced vHIT-discordant caloric abnormal classifications compared with 25% while maintaining close correspondence with the vHIT-defined classification. Conclusion: In patients evaluated within 72 h of acute vertigo onset, a CP threshold of approximately 30% showed the closest correspondence with vHIT-defined unilateral high-frequency vestibular dysfunction. It should be interpreted as a practical benchmark for interpreting caloric CP in relation to vHIT findings, not as an independent diagnostic criterion for AUVP.