Yulia Valko

Vestibular Labyrinth Contributions to Human Whole-Body Motion Discrimination

To assess the contributions of the vestibular system to whole-body motion discrimination in the dark, we measured direction recognition thresholds as a function of frequency for yaw rotation, superior–inferior translation (“z-translation”), interaural translation (“y-translation”), and roll tilt for 14 normal subjects and for 3 patients following total bilateral vestibular ablation. The patients had significantly higher average threshold measurements than normal (p < 0.01) for yaw rotation (depending upon frequency, 5.4× to 15.7× greater), z-translation (8.3× to 56.8× greater), y-translation (1.7× to 4.5× greater), and roll tilt (1.3× to 3.0× greater)—establishing the predominant contributions of the vestibular system for these motions in the dark.

Motion Perception in Patients with Idiopathic Bilateral Vestibular Hypofunction.

We measured vestibular perceptual thresholds in patients with idiopathic bilateral vestibulopathy to assess the distribution of peripheral vestibular damage in this disorder. Thresholds were measured with standard psychometric techniques in 4 patients and compared with thresholds in normal subjects and patients with completely absent peripheral vestibular function. Motion paradigms included yaw rotation (testing the lateral canals), interaural translation (testing the utricles), superior-inferior translation (testing the saccules), and roll tilt (testing the vertical semicircular canals and the otolith organs). We found that perceptual thresholds were abnormally elevated in the patients with idiopathic bilateral vestibulopathy for yaw rotation at all frequencies and for interaural translation at only the lower frequencies. Thresholds were normal for the other 2 motion paradigms. The results demonstrate that the distribution of vestibular dysfunction in this disorder is not uniform but, rather, can affect lateral canal and utricular thresholds while relatively sparing vertical canal and saccular function.

Relative diagnostic value of ocular vestibular evoked potentials and the subjective visual vertical during tilt and eccentric rotation

OBJECTIVEnWe compared vibration-induced ocular vestibular evoked myogenic potentials (OVEMPs) with the visual vertical during whole-body roll tilt and eccentric rotation in healthy subjects and patients with unilateral vestibular loss, to determine which test was most sensitive in discriminating impaired utricle function.nnnMETHODSnOVEMPs and the visual vertical were measured in 11 patients and 11 healthy subjects. Visual vertical was measured during roll tilts between -9.6° and 9.6°, and during rotation at 400°/s with the head upright and the vertical rotation axis located between ±3.5 cm from the head center.nnnRESULTSnOVEMPs in patients were strikingly asymmetric, whereas they were approximately symmetric in healthy subjects. Patients showed impaired visual vertical gain during eccentric rotation and increased errors for both roll tilt and eccentric rotation tests. OVEMPs were superior at discriminating between patients and healthy subjects, although eccentric rotation performed nearly as well.nnnCONCLUSIONSnOVEMPs provide a powerful test for discriminating between healthy subjects and patients with chronic unilateral vestibular loss, and testing the visual vertical testing during eccentric rotation was superior to testing during whole-body roll tilt.nnnSIGNIFICANCEnOVEMPs are easier to administer, less demanding on patients, and in general are more effective at identifying chronic unilateral vestibular loss than visual vertical measurements.

Ocular vestibular evoked myogenic potentials as a test for myasthenia gravis.

Objective: To explore whether ocular vestibular evoked myogenic potentials (oVEMP) can be used to detect a decrement in the extraocular muscle activity of patients with myasthenia gravis (MG). Methods: Twenty-seven patients with MG, including 13 with isolated ocular and 14 with generalized MG, and 28 healthy controls participated. We applied repetitive vibration stimuli to the forehead and recorded the activity of the inferior oblique muscle with 2 surface electrodes placed beneath the eyes. To identify the oVEMP parameters with the highest sensitivity and specificity, we evaluated the decrement over 10 stimulus repetitions at 3 different repetition rates (3 Hz, 10 Hz, and 20 Hz). Results: Repetitive stimulation at 20 Hz yielded the best differentiation between patients with MG and controls with a sensitivity of 89% and a specificity of 64% when using a unilateral decrement of ≥15.2% as cutoff. When using a bilateral decrement of ≥20.4% instead, oVEMP allowed differentiation of MG from healthy controls with 100% specificity, but slightly reduced sensitivity of 63%. For both cutoffs, sensitivity was similar in isolated ocular and generalized MG. Conclusion: Our study demonstrates that the presence of an oVEMP decrement is a sensitive and specific marker for MG. This test allows direct and noninvasive examination of extraocular muscle activity, with similarly good diagnostic accuracy in ocular and generalized MG. Thus, oVEMP represents a promising diagnostic tool for MG. Classification of evidence: This study provides Class III evidence that oVEMP testing accurately identifies patients with MG with ocular symptoms (sensitivity 89%, specificity 64%).

Experimental parameter estimation of a visuo-vestibular interaction model in humans

Visuo-vestibular interactions in monkeys can be accurately modelled using the classical Raphan and Cohens model. This model is composed of direct vestibular and visual contributions to the vestibulo-ocular reflex (VOR) and of a velocity storage. We applied this model to humans and estimated its parameters in a series of experiments: yaw rotations at moderate (60°/s) and high velocities (240°/s), suppression of the VOR by a head-fixed wide-field visual stimulus, and optokinetic stimulation with measurements of optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN). We found the velocity storage time constant to be 13 s, which decreased to 8 s during visual suppression. OKAN initial velocity was 12% of the OKN stimulus velocity. The gain of the direct visual pathway was 0.75 during both visual suppression and OKN; however, the visual input to the velocity storage was higher during visual suppression than during OKN. We could not estimate the time constant of the semicircular canals accurately. Finally, we inferred from high-velocity rotations that the velocity storage saturates around 20-30°/s. Our results indicate that the dynamics of visuo-vestibular interactions in humans is similar as in monkeys. The central integration of visual cues, however, is weaker in humans.

Automated Romberg testing in patients with benign paroxysmal positional vertigo and healthy subjects.

Objective: Benign paroxysmal positional vertigo (BPPV) is the most common cause of dizziness. The underlying pathomechanism responsible for the recurrent vertigo attacks has been elucidated in detail and highly effective treatment strategies (liberation maneuvers) have been developed. However, many BPPV patients complain about problems of balance especially following liberation maneuvers. Aim: To objectively demonstrate differences in balance performance in BPPV patients compared to healthy subjects both prior and after BPPV liberation maneuvers. Methods: Seven patients with BPPV of the posterior semicircular canal and nine healthy subjects participated. To assess balance while standing, we analyzed the location and temporal stability of the center of pressure recorded by pressure-sensitive electronic soles during Romberg testing (on stable ground and on foam) and tandem stand. To assess regularity of gait, we analyzed the step frequency during walking of 50 m. All tests were performed prior and after liberation maneuvers in both groups. Results: Healthy subjects and patients differ significantly in their balance performance and use different stabilization strategies both prior and after liberation maneuvers. Both Romberg tests indicated poorer balance in BPPV patients (mean COP shifted towards toes), especially in posttreatment tests, while tandem stand appeared unaltered. We did not observe differences in escorted (by an experimenter) walking regularities between patients and healthy subjects and between pre- and post-maneuver testing. Conclusion and significance: Our findings confirm the typical clinical observation of a further posttreatment deterioration of already impaired postural performance in BPPV patients. While the etiology and the time course of this peculiar problem warrants further studies, the treating physician should be familiar with this transient side effect of therapeutic maneuvers to provide adequate counseling of patients. Finally, we successfully demonstrated the pressure-sensitive electronic soles as a new and potentially useful tool for both clinical and research purposes.

Validation of the Russian version of the Fatigue Impact Scale and Fatigue Severity Scale in multiple sclerosis patients

Fatigue is a common complaint in patients with multiple sclerosis (MS), and its detection and monitoring are based on self‐reported questionnaires. The objective of this study was to validate the Russian translation of the Fatigue Impact Scale (FIS) and the Fatigue Severity Scale (FSS) in MS patients and controls.

Cerebellar contributions to self-motion perception: evidence from patients with congenital cerebellar agenesis

The cerebellum was historically considered a brain region dedicated to motor control, but it has become clear that it also contributes to sensory processing, particularly when sensory discrimination is required. Prior work, for example, has demonstrated a cerebellar contribution to sensory discrimination in the visual and auditory systems. The cerebellum also receives extensive inputs from the motion and gravity sensors in the vestibular labyrinth, but its role in the perception of head motion and orientation has received little attention. Drawing on the lesion-deficit approach to understanding brain function, we evaluated the contributions of the cerebellum to head motion perception by measuring perceptual thresholds in two subjects with congenital agenesis of the cerebellum. We used a set of passive motion paradigms that activated the semicircular canals or otolith organs in isolation or combination, and compared results of the agenesis patients with healthy control subjects. Perceptual thresholds for head motion were elevated in the agenesis subjects for all motion protocols, most prominently for paradigms that only activated otolith inputs. These results demonstrate that the cerebellum increases the sensitivity of the brain to the motion and orientation signals provided by the labyrinth during passive head movements.

Fatigue in patients with myasthenia gravis

BackgroundThe subjective feeling of fatigue in myasthenia gravis (MG) is poorly elucidated, in part because it is often confounded with the objective sign of muscle fatigability. Another reason is the paucity of validated fatigue questionnaires in MG.MethodsWe applied the 9-item Fatigue Severity Scale (FSS) and the 40-item Fatigue Impact Scale (FIS) to 73 MG patients and 230 age- and sex-matched control subjects. We ascertained levels of education, marital status, and comorbidities such as depression, sleepiness, sleep times and sleep debt. Disease severity was graded according to the Myasthenia Gravis Foundation of America (MGFA) classification.ResultsAll fatigue scores, with the exception of the cognitive FIS subscale, were higher in MG patients than controls. In MG, the prevalence of fatigue (defined by FSS scoresu2009≥u20094.0) was 70%. Multiple regression analyses revealed several independent associates of fatigue, including depression (all fatigue scales), MGFA stage (FSS, physical FIS), female sex (cognitive and psychosocial FIS), and sleep debt (physical FIS).ConclusionFatigue in MG is highly prevalent, mainly physical, and influenced by depressive symptoms, disease severity, female sex and sleep debt. Cognitive fatigue in MG may not be a direct disease manifestation, but secondary to depression. The FSS and FIS represent reliable and validated tools, appropriate to discern meaningful clinical aspects of fatigue in MG. Clinical recognition of the complexity of fatigue may foster individualized treatment approaches for affected MG patients.

Mystery Case: Don't fall for pseudo-INO!

A 31-year-old woman with a 4-day history of diplopia showed slow adducting saccades in the left eye (pseudo–internuclear ophthalmoplegia [P-INO]1,2; see video 1 at Neurology.org), left inferior rectus muscle weakness, and upper limb fatigability. Edrophonium testing with transient resolution of P-INO led to a diagnosis of myasthenia gravis (MG) (see video 2), which was later confirmed by positive acetylcholine receptor antibodies.