Verticality perception in patients with active multiple sclerosis: The applicability of subjective visual vertical test and its modifications

•Dynamic visual stimulus and head tilts are beneficial when testing MS patients.•Modified SVV may be more beneficial than standard testing for MS patients.•A-effect is a potential sign of spatial orientation disturbance at 30° head tilt.•In head-tilt testing, the direction of SVV tilt is more significant than its magnitude. Dizziness and balance disturbances are common in patients with MS. Subjective visual vertical (SVV) is a test of vestibular perception that allows clinicians to evaluate the integration of multiple sensory inputs for spatial orientation in the CNS. We hypothesize that central vestibular impairment caused by active MS lesions may be reflected in the modified SVV testing. To evaluate the applicability of dynamic and head-tilt SVV for detecting spatial orientation disturbances in MS patients and compare it with conventional SVV testing. The SVV test was conducted using the virtual reality application VIRVEST. SVV was measured in static and dynamic conditions during head upright, and 30° right and left lateral head tilts. The study group comprised 36 patients with active MS and 40 controls. Greater SVV errors were found in MS patients during upright testing; however, dynamic conditions increased the test's sensitivity. Lateral head tilts affected the perception of verticality in both groups; however, the absolute values of SVV biases were paradoxically greater in controls. Potentially pathological A-effect was found in 75 % of MS patients and 17,5 % of controls (p < 0,001), as SVV was more likely to shift towards the side of the head tilt in the MS group. Lateral head tilts and dynamic conditions are valuable additions to the SVV test for detecting disturbances in spatial orientation during active MS. The direction of SVV shifts during lateral head tilts may be more clinically significant than the magnitude of SVV errors for this patient group.