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

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.

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.

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.

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.