Normal horizontal VOR gain and catch-up saccades: still a diagnostic dilemma

Purpose: To analyze the relationship between normal horizontal vestibular-ocular reflex (VOR) gain with catch-up saccades (CS) in patients reporting recurrent or chronic vestibular symptoms of unknown causes. Methods: A prospective study involving 34 patients suffering from vestibular symptoms of unknown origin; all subjects presented bilateral normal horizontal VOR gain and CS on at least one side. Data collection regarded onset and duration of vestibular symptoms. vHIT parameters were analyzed. Results: Patients complained of episodic spontaneous vertigo in 54.54% of cases, dizziness in 12.12%, and unsteadiness in 33.33% respectively. The study of VOR gain evidenced a mean gain of 0.92 ± 0.08 for the right and of 0.89 ± 0.07 for the left horizontal semicircular canal (HSC) (p = 0.11). A weak inverse correlation between age and VOR gain (r=-0.007232, p = 0.954) was found. CS were observed bilaterally in 66.66% of subjects, with overt saccades in 78.78% of HSC. All detected CS presented a peak velocity between 100 and 200 °/s with a scattered pattern of saccade distribution in 75.86% of cases. HSC with a VOR gain between 0.8 and 0.89 exhibited the highest prevalence (84.37%) of overt saccades (p = 0.01). No relationship was found between CS laterality, the clusterization of saccades, and different vertigo symptoms. Conclusion: Patients suffering from vertigo of unknown origin with a normal VOR gain and CS displayed a CS pattern that was mainly represented by overt saccades with a scattered pattern that may be an indirect sign of an underlying vestibular dysfunction; clinicians should include a careful analysis of CS patterns and metrics to better explore vestibular function.