Saccular function less affected than canal function in bilateral vestibulopathy

Abstract

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, electronystagmography 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 microV in the patients vs. 130.8 +/- 85.9 microV 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.

Bilateral Vestibular Hypofunction: Challenges in Establishing the Diagnosis in Adults

“…Firstly, each test has its own limitations in terms of sensitivity, specificity, patient acceptance, costs and duration, and there is still no consensus about diagnostic criteria for BVH [7]. Secondly, since BVH probably represents a functionally heterogeneous disorder with different combined or isolated deficits of the vestibular system, different results from laboratory tests can be expected for different types of BVH [18,80,81]. Thirdly, the output parameters of laboratory tests such as the caloric test, rotatory chair tests and (video) head impulse testing [(V)HIT] show a considerable overlap between patients and healthy subjects [82].…”

“…However, while it is necessary to take the total response into account, there is still no consensus on the range of responses required for the diagnosis of BVH [7,10,118,127]. A criterion often suggested for diagnosing BVH is to have a sum of 4 irrigations that is less than 20°/s [7,12,18,95]. While this is highly specific, it could still lead to false-positive results (partly due to the anatomical variations mentioned above) and also, very importantly, to false-negative results.…”

“…Other patients had vertigo attacks, and even though they did not have hearing loss, this could be a first sign of Menière's disease, since some of them were still young (below 45 years). Although it is most likely that BVH can affect different parts of the vestibular system separately [18,19], an absent response of VEMPs does not indicate a vestibular deficit per se.…”

“…magnetic resonance imaging, computed tomography), lumbar puncture, sensory nerve action potentials, speech assessment, etc. [18,19,20,23,40,89]. However, these tests are mainly used for determination of coexisting problems or the etiology of BVH (table 1), not for an evaluation of vestibular function.…”

“…Nowadays, this symptom complex is known to have many causes, and BVH probably represents a functionally heterogeneous disorder with different combined or isolated deficits of the semicircular canals and/or otolith organs [18]. Most of the etiologies described are presented in table 1[12,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44]. However, its etiology still remains unclear in approximately 50% of all cases [7,19].…”