Saccular function less affected than canal function in bilateral vestibulopathy

Bilateral vestibulopathy (BV) is characterized by impaired or lost function of both labyrinths or eighth nerves. The diagnosis is routinely established by the head-thrust test, caloric irrigation and rotational testing with electronystagmography to determine the high- and low-frequency deficit of the vestibulo-ocular reflex. All three methods evaluate semicircular canal function only. Vestibular-evoked myogenic potentials (VEMPs) provide a measure of saccular otolith function. The aim of this study was to evaluate the frequency and extent of saccular dysfunction in patients with BV and to correlate saccular with horizontal semicircular canal dysfunction. A total of 84 BV-patients (23 females, mean age 62 +/- 15 (SD) years at the time of diagnosis assessment) were examined with VEMPs, electronystagrnography with caloric irrigation and a standardized neuro-ophthalmological and -otological examination; 47 healthy subjects (18 females, mean 56 19 years) served as controls. Amplitudes P1-N1 were significantly lower in patients with BV compared to controls (mean P1-N1 of all ears 82.1 +/- 50.7 mu V in the patients vs. 130.8 +/- 85.9 mu V in healthy volunteers). VEMPs were absent unilaterally in four patients with BV and in none bilaterally. In contrast, caloric responses were absent bilaterally in 40 patients. There was no correlation between amplitude P1-N1 and caloric-induced nystagmus. The latencies P1 and N1 were not significantly different between patients and controls. Thus, in our study population saccular function appeared to be less affected than horizontal semicircular canal function.