Subjective visual vertical in peripheral unilateral vestibular diseases

In humans, the perception of vertical is provided by input from various sensorineural organs and pathways: vision, eye-movements, and proprioceptive and vestibular cues, particularly from the otolithic organs and graviceptive pathways. Well known in several types of brainstem lesions, subjective visual vertical (SVV) abnormalities may also be observed after peripheral vestibular lesions, such as surgical deafferentation, with a deviation directed toward the operated ear. Subjective visual vertical abnormalities are presumably related to a lesion of the otolithic organs and/or to changes in the afferent graviceptive pathways. The goal of this prospective study was to measure the SVV and to define the influence of the otolithic organs in patients suffering from various types of peripheral vestibular diseases: unilateral sudden cochleo-vestibular loss, so-called "viral labyrinthitis" (VL), sudden idiopathic unilateral peripheral vestibular loss, so-called "vestibular neuritis" (Ne). Data were compared with findings after unilateral surgical deafferentations such as vestibular neurectomy (VN) and labyrinthectomy (Lab). Subjective visual vertical was measured with a binocular test (vertical frame) and a monocular test (Maddox rod). In all patients, after VN and Lab, the SVV showed a 10-30 degrees tilt with the vertical frame (N: 0 +/- 2 degrees), 5-15 degrees with the Maddox rod (N: 0 +/- 4 degrees). With the vertical frame, SVV was tilted > 2 degrees in VL (47%) and in Ne (37%); the Maddox rod showed a > 4 degrees tilt in VL (41%) and in Ne (42%). The tilt was directed toward the affected ear. Our results demonstrate that SVV is frequently tilted in acute peripheral vestibulopathies such as VL and Ne. These findings suggest that otolithic function is implicated in the deficit depending on the extent and/or the localisation of the peripheral vestibular lesion.