Temporal changes of subjective visual vertical in patients with vestibular neuritis

Introduction: During the acute phase, patients with vestibular neuritis suffer from severe vertigo. With time, the intensity of vertigo gradually decreases. The aims of the present study were: (1) to determine whether changes in the subjective visual vertical (SVV) system reflect how patients subjectively experience vertigo, and (2) to determine the relationship between changes in SVV and canal paralysis (CP). Methods: Our subjects comprised 23 patients with vestibular neuritis. We measured the SVV of each patient several times to evaluate the recovery of SVV and CP over time. The intensity of vertigo was graded numerically as follows: (1) 5 - very intense (patient cannot stand with eyes open), (2) 4 - intense (patient cannot stand with eyes closed), (3) 3 - moderate (patient can stand with eyes closed), (4) 2 - slight vertigo, and (5) 1 - no vertigo. We also evaluated CP in 10 patients using the thermal caloric test. Results: The temporal process of SVV recovery was grouped into three categories: (1) small fluctuation/rapid recovery (N=7); (2) small fluctuation/delayed recovery (N=8); and (3) large fluctuation (N=8). For CP recovery, we observed cases that failed to recover (N=4) and others that did recover (N=6). When tested 30 days and 1 year after the initial examination, the CP recovery group displayed larger SVV fluctuations accompanied by intense subjective vertigo, whereas the group that did not recover exhibited fewer fluctuations accompanied by weak vertigo. Conclusions: SVV represents the subjective perception of the direction of gravity. Fluctuations in SVV, rather than absolute SVV, correlate well with the subjective intensity of vertigo. This suggests that, during the recovery process, fluctuations in SVV, rather than the dysfunction itself, causes dizziness. Measuring SVV is very straightforward and quantifying SVV fluctuations is an effective measure of the intensity of vertigo.