The minimal clinically important difference for gait speed in significant unilateral vestibular hypofunction after vestibular rehabilitation.

Gait speed is a valid measure of both physical function and vestibular health. Vestibular rehabilitation is useful to improve gait speed for patients with vestibular hypofunction, yet there is little data to indicate how changes in gait speed reflect changes in patient-reported health outcomes. We determined the minimal clinically important difference in the gait speed of patients with unilateral vestibular hypofunction, mostly due to deafferentation surgery, as anchored to the Dizziness Handicap Index and the Activities Balance Confidence scale, validated using regression analysis, change difference, receiver-operator characteristic curve, and average change methods. After six weeks of vestibular rehabilitation, a change in gait speed from 0.20 to 0.34 m/s with 95% confidence was required for the patients to perceive a significant reduction in perception of dizziness and improved balance confidence.

Vestibular Rehabilitation for Peripheral Vestibular Hypofunction: An Updated Clinical Practice Guideline From the Academy of Neurologic Physical Therapy of the American Physical Therapy Association.

BACKGROUND: Uncompensated vestibular hypofunction can result in symptoms of dizziness, imbalance, and/or oscillopsia, gaze and gait instability, and impaired navigation and spatial orientation; thus, may negatively impact an individual's quality of life, ability to perform activities of daily living, drive, and work. It is estimated that one-third of adults in the United States have vestibular dysfunction and the incidence increases with age. There is strong evidence supporting vestibular physical therapy for reducing symptoms, improving gaze and postural stability, and improving function in individuals with vestibular hypofunction. The purpose of this revised clinical practice guideline is to improve quality of care and outcomes for individuals with acute, subacute, and chronic unilateral and bilateral vestibular hypofunction by providing evidence-based recommendations regarding appropriate exercises. METHODS: These guidelines are a revision of the 2016 guidelines and involved a systematic review of the literature published since 2015 through June 2020 across 6 databases. Article types included meta-analyses, systematic reviews, randomized controlled trials, cohort studies, case-control series, and case series for human subjects, published in English. Sixty-seven articles were identified as relevant to this clinical practice guideline and critically appraised for level of evidence. RESULTS: Based on strong evidence, clinicians should offer vestibular rehabilitation to adults with unilateral and bilateral vestibular hypofunction who present with impairments, activity limitations, and participation restrictions related to the vestibular deficit. Based on strong evidence and a preponderance of harm over benefit, clinicians should not include voluntary saccadic or smooth-pursuit eye movements in isolation (ie, without head movement) to promote gaze stability. Based on moderate to strong evidence, clinicians may offer specific exercise techniques to target identified activity limitations and participation restrictions, including virtual reality or augmented sensory feedback. Based on strong evidence and in consideration of patient preference, clinicians should offer supervised vestibular rehabilitation. Based on moderate to weak evidence, clinicians may prescribe weekly clinic visits plus a home exercise program of gaze stabilization exercises consisting of a minimum of: (1) 3 times per day for a total of at least 12 minutes daily for individuals with acute/subacute unilateral vestibular hypofunction; (2) 3 to 5 times per day for a total of at least 20 minutes daily for 4 to 6 weeks for individuals with chronic unilateral vestibular hypofunction; (3) 3 to 5 times per day for a total of 20 to 40 minutes daily for approximately 5 to 7 weeks for individuals with bilateral vestibular hypofunction. Based on moderate evidence, clinicians may prescribe static and dynamic balance exercises for a minimum of 20 minutes daily for at least 4 to 6 weeks for individuals with chronic unilateral vestibular hypofunction and, based on expert opinion, for a minimum of 6 to 9 weeks for individuals with bilateral vestibular hypofunction. Based on moderate evidence, clinicians may use achievement of primary goals, resolution of symptoms, normalized balance and vestibular function, or plateau in progress as reasons for stopping therapy. Based on moderate to strong evidence, clinicians may evaluate factors, including time from onset of symptoms, comorbidities, cognitive function, and use of medication that could modify rehabilitation outcomes. DISCUSSION: Recent evidence supports the original recommendations from the 2016 guidelines. There is strong evidence that vestibular physical therapy provides a clear and substantial benefit to individuals with unilateral and bilateral vestibular hypofunction. LIMITATIONS: The focus of the guideline was on peripheral vestibular hypofunction; thus, the recommendations of the guideline may not apply to individuals with central vestibular disorders. One criterion for study inclusion was that vestibular hypofunction was determined based on objective vestibular function tests. This guideline may not apply to individuals who report symptoms of dizziness, imbalance, and/or oscillopsia without a diagnosis of vestibular hypofunction. DISCLAIMER: These recommendations are intended as a guide to optimize rehabilitation outcomes for individuals undergoing vestibular physical therapy. The contents of this guideline were developed with support from the American Physical Therapy Association and the Academy of Neurologic Physical Therapy using a rigorous review process. The authors declared no conflict of interest and maintained editorial independence.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A369).

How to diagnose cervicogenic dizziness.

Cervicogenic dizziness (CGD) is a clinical syndrome characterized by the presence of dizziness and associated neck pain. There are no definitive clinical or laboratory tests for CGD and therefore CGD is a diagnosis of exclusion. It can be difficult for healthcare professionals to differentiate CGD from other vestibular, medical and vascular disorders that cause dizziness, requiring a high level of skill and a thorough understanding of the proper tests and measures to accurately rule in or rule out competing diagnoses. Consequently, the purpose of this paper is to provide a systematic diagnostic approach to enable healthcare providers to accurately diagnose CGD. This narrative will outline a stepwise process for evaluating patients who may have CGD and provide steps to exclude diagnoses that can present with symptoms similar to those seen in CGD, including central and peripheral vestibular disorders, vestibular migraine, labyrinthine concussion, cervical arterial dysfunction, and whiplash associated disorder.

Vestibular Rehabilitation for Peripheral Vestibular Hypofunction: An Evidence-Based Clinical Practice Guideline: FROM THE AMERICAN PHYSICAL THERAPY ASSOCIATION NEUROLOGY SECTION.

BACKGROUND: Uncompensated vestibular hypofunction results in postural instability, visual blurring with head movement, and subjective complaints of dizziness and/or imbalance. We sought to answer the question, "Is vestibular exercise effective at enhancing recovery of function in people with peripheral (unilateral or bilateral) vestibular hypofunction?" METHODS: A systematic review of the literature was performed in 5 databases published after 1985 and 5 additional sources for relevant publications were searched. Article types included meta-analyses, systematic reviews, randomized controlled trials, cohort studies, case control series, and case series for human subjects, published in English. One hundred thirty-five articles were identified as relevant to this clinical practice guideline. RESULTS/DISCUSSION: Based on strong evidence and a preponderance of benefit over harm, clinicians should offer vestibular rehabilitation to persons with unilateral and bilateral vestibular hypofunction with impairments and functional limitations related to the vestibular deficit. Based on strong evidence and a preponderance of harm over benefit, clinicians should not include voluntary saccadic or smooth-pursuit eye movements in isolation (ie, without head movement) as specific exercises for gaze stability. Based on moderate evidence, clinicians may offer specific exercise techniques to target identified impairments or functional limitations. Based on moderate evidence and in consideration of patient preference, clinicians may provide supervised vestibular rehabilitation. Based on expert opinion extrapolated from the evidence, clinicians may prescribe a minimum of 3 times per day for the performance of gaze stability exercises as 1 component of a home exercise program. Based on expert opinion extrapolated from the evidence (range of supervised visits: 2-38 weeks, mean = 10 weeks), clinicians may consider providing adequate supervised vestibular rehabilitation sessions for the patient to understand the goals of the program and how to manage and progress themselves independently. As a general guide, persons without significant comorbidities that affect mobility and with acute or subacute unilateral vestibular hypofunction may need once a week supervised sessions for 2 to 3 weeks; persons with chronic unilateral vestibular hypofunction may need once a week sessions for 4 to 6 weeks; and persons with bilateral vestibular hypofunction may need once a week sessions for 8 to 12 weeks. In addition to supervised sessions, patients are provided a daily home exercise program. DISCLAIMER: These recommendations are intended as a guide for physical therapists and clinicians to optimize rehabilitation outcomes for persons with peripheral vestibular hypofunction undergoing vestibular rehabilitation.Video Abstract available for more insights from the author (see Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A124).

The effects of habituation and gaze stability exercises in the treatment of unilateral vestibular hypofunction: a preliminary results.

BACKGROUND AND PURPOSE: The efficacy of both habituation and adaptation exercise interventions in the treatment of unilateral vestibular hypofunction has been demonstrated by previous studies. The purpose of this article is to describe the preliminary results of an ongoing study that compares the effects of these 2 different exercise approaches on outcomes related to vestibular function. METHODS: Seven participants with unilateral vestibular hypofunction completed a 6-week exercise intervention after random assignment to either habituation exercises or gaze stability (GS) adaptation exercises. The following measures were performed pre- and posttreatment: Dizziness Handicap Inventory to measure the symptom impact, motion sensitivity quotient (MSQ) to assess sensitivity to head movements, and the dynamic visual acuity (DVA) test as a measure of GS during head movements. RESULTS: After the 6-week intervention, there was an overall improvement in the Dizziness Handicap Inventory, the MSQ score, and both the active and passive DVA. The habituation and GS intervention group participants each demonstrated similar improvements in both the MSQ score and the active and passive DVA measures. DISCUSSION AND CONCLUSIONS: The improvement in the MSQ score for the GS group and the improvement in the DVA measures for the habituation group were unexpected findings. Head movement, which is required by both exercise interventions, rather than the specific type of exercise may be the critical factor underlying the observed improvements in motion sensitivity and DVA.

Mechanism of dynamic visual acuity recovery with vestibular rehabilitation.

OBJECTIVE: To determine why dynamic visual acuity (DVA) improves after vestibular rehabilitation in people with vestibular hypofunction. DESIGN: Combined descriptive and intervention study. SETTING: Outpatient department in an academic medical institution. PARTICIPANTS: Five patients (age, 42-66 y) and 4 age-matched controls (age, 39-67 y) were studied. Patients had vestibular hypofunction (mean duration, 177+/-188 d) identified by clinical (positive head thrust test, abnormal DVA), physiologic (reduced angular vestibulo-ocular reflex [aVOR] gain during passive head thrust testing), and imaging examinations (absence of tumor in the internal auditory canals or cerebellopontine angle). INTERVENTION: Vestibular rehabilitation focused on gaze and gait stabilization (mean, 5.0+/-1.4 visits; mean, 66+/-24 d). The control group did not receive any intervention. MAIN OUTCOME MEASURES: aVOR gain (eye velocity/head velocity) during DVA testing (active head rotation) and horizontal head thrust testing (passive head rotation) to control for spontaneous recovery. RESULTS: For all patients, DVA improved (mean, 51%+/-25%; range, 21%-81%). aVOR gain during the active DVA test increased in each of the patients (mean range, 0.7+/-0.2 to 0.9+/-0.2 [35%]). aVOR gain during passive head thrust did not improve in 3 patients and improved only partially in the other 2. For control subjects, aVOR gain during DVA was near 1. CONCLUSIONS: Our data suggest that vestibular rehabilitation increases aVOR gain during active head rotation independent of peripheral aVOR gain recovery.

Retention of VOR gain following short-term VOR adaptation.

Motor learning in the vestibular system can be differentially obtained depending upon the context for which the vestibulo-ocular reflex (VOR) has been exposed. Manipulating head orientation relative to gravity is an example of a contextual cue that can elicit independent VOR gains. We were interested in examining retention of short-term VOR adaptation when the adapting stimulus was paired with a novel contextual cue. Two sets of non-human primate VOR adaptation experiments were designed to assess the influence of head position relative to gravity on retention of the pitch VOR. First, the pitch VOR of three squirrel monkeys was adapted for 3 h using minimizing (x0.45) spectacles and a sum-of-sines stimulus (20 degrees /s at 0.5, 1.1, 2.3, and 3.7 Hz) while the animals were positioned left ear down (LED adaptation). Pitch VOR gains were measured in the adapted position (LED) and two non-adapted positions (upright, UP) or right ear down (RED). In the second set of experiments, the pitch VOR was adapted in an upright head position (same adapting stimulus as used in LED) and tested in UP, LED or RED. No head immobility or darkness restrictions were imposed on the animals after the initial adaptation exposure. The pitch VOR gains were measured during the acceleration (G (A)) and constant velocity (G (V)) portions of 1,000 degrees /s(2)-150 degrees /s step responses and during 0.5, 2.0, and 4.0 Hz sinusoids with velocities varying from 20 to 100 degrees /s. All measures of VOR gain for UP, LED, and RED were done immediately after the adaptation and for three subsequent days and at post-adaptation day 7 (PAD 7). When tested in the adapting position, all experiments showed immediate reduction in G (A) and G (V) compared with pre-adaptation levels. For LED adaptation experiments, the pitch G (A) and G (V) gains were significantly reduced for as long as 7 days. Some retention of the LED-adapted VOR gain also occurred when testing in the RED position. No retention of pitch VOR G (A) or G (V) existed for the UP position after adaptation in LED. After the UP-adapt experiments, no retention of the G (A) or G (V) was found when tested in the adapting position. Interestingly, however, some retention of G (A) and G (V) did exist when the UP-adapted animals were tested in LED or RED. Data from sinusoidal rotations followed a similar adaptation pattern as the step responses. Our findings show that after only 3 h of adaptation exposure, adaptation of the pitch VOR gain is retained for several days. This long-term retention of VOR adaptation after short-term exposure appears to be the result of inducing adaptation with an atypical combination of movement and position for the monkey (LED-adapt). Our results indicate that head orientation relative to gravity is an effective context for retaining learned VOR gains in addition to restricting mobility or keeping animals in the dark. We also show that the adapting head position determines the magnitude of VOR adaptation.

Axis of eye rotation changes with head-pitch orientation during head impulses about earth-vertical.

The goal of this study was to assess how the axis of head rotation, Listing's law, and eye position influence the axis of eye rotation during brief, rapid head rotations. We specifically asked how the axis of eye rotation during the initial angular vestibuloocular reflex (VOR) changed when the pitch orientation of the head relative to Earth-vertical was varied, but the initial position of the eye in the orbit and the orientation of Listing's plane with respect to the head were fixed. We measured three-dimensional eye and head rotation axes in eight normal humans using the search coil technique during head-and-trunk (whole-body) and head-on-trunk (head-only) "impulses" about an Earth-vertical axis. The head was initially oriented at one of five pitch angles (30 degrees nose down, 15 degrees nose down, 0 degrees, 15 degrees nose up, 30 degrees nose up). The fixation target was always aligned with the nasooccipital axis. Whole-body impulses were passive, unpredictable, manual, rotations with peak-amplitude of approximately 20 degrees , peak-velocity of approximately 80 degrees /s, and peak-acceleration of approximately 1000 degrees /s2. Head-only impulses were also passive, unpredictable, manual, rotations with peak-amplitude of approximately 20 degrees , peak-velocity of approximately 150 degrees /s, and peak-acceleration of approximately 3000 degrees /s2. During whole-body impulses, the axis of eye rotation tilted in the same direction, and by an amount proportional (0.51 +/- 0.09), to the starting pitch head orientation (P < 0.05). This proportionality constant decreased slightly to 0.39 +/- 0.08 (P < 0.05) during head-only impulses. Using the head-only impulse data, with the head pitched up, we showed that only 50% of the tilt in the axis of eye rotation could be predicted from vectorial summation of the gains (eye velocity/head velocity) obtained for rotations about the pure yaw and roll head axes. Thus, even when the orientation of Listing's plane and eye position in the orbit are fixed, the axis of eye rotation during the VOR reflects a compromise between the requirements of Listing's law and a perfectly compensatory VOR.

The three-dimensional vestibulo-ocular reflex evoked by high-acceleration rotations in the squirrel monkey.

The aim of this study was to determine if the angular vestibulo-ocular reflex (VOR) in response to pitch, roll, left anterior-right posterior (LARP), and right anterior-left posterior (RALP) head rotations exhibited the same linear and nonlinear characteristics as those found in the horizontal VOR. Three-dimensional eye movements were recorded with the scleral search coil technique. The VOR in response to rotations in five planes (horizontal, vertical, torsional, LARP, and RALP) was studied in three squirrel monkeys. The latency of the VOR evoked by steps of acceleration in darkness (3,000 degrees /s(2) reaching a velocity of 150 degrees /s) was 5.8+/-1.7 ms and was the same in response to head rotations in all five planes of rotation. The gain of the reflex during the acceleration was 36.7+/-15.4% greater than that measured at the plateau of head velocity. Polynomial fits to the trajectory of the response show that eye velocity is proportional to the cube of head velocity in all five planes of rotation. For sinusoidal rotations of 0.5-15 Hz with a peak velocity of 20 degrees /s, the VOR gain did not change with frequency (0.74+/-0.06, 0.74+/-0.07, 0.37+/-0.05, 0.69+/-0.06, and 0.64+/-0.06, for yaw, pitch, roll, LARP, and RALP respectively). The VOR gain increased with head velocity for sinusoidal rotations at frequencies > or =4 Hz. For rotational frequencies > or =4 Hz, we show that the vertical, torsional, LARP, and RALP VORs have the same linear and nonlinear characteristics as the horizontal VOR. In addition, we show that the gain, phase and axis of eye rotation during LARP and RALP head rotations can be predicted once the pitch and roll responses are characterized.

Vergence-dependent adaptation of the vestibulo-ocular reflex.

The gain of the vestibulo-ocular reflex (VOR) normally depends on the distance between the subject and the visual target, but it remains uncertain whether vergence angle can be linked to changes in VOR gain through a process of context-dependent adaptation. In this study, we examined this question with an adaptation paradigm that modified the normal relationship between vergence angle and retinal image motion. Subjects were rotated sinusoidally while they viewed an optokinetic (OKN) stimulus through either diverging or converging prisms. In three subjects the diverging prisms were worn while the OKN stimulus moved out of phase with the head, and the converging prisms were worn when the OKN stimulus moved in-phase with the head. The relationship between the vergence angle and OKN stimulus was reversed in the fourth subject. After 2 h of training, the VOR gain at the two vergence angles changed significantly in all of the subjects, evidenced by the two different VOR gains that could be immediately accessed by switching between the diverged and converged conditions. The results demonstrate that subjects can learn to use vergence angle as the contextual cue that retrieves adaptive changes in the angular VOR.

Differential adaptation of the linear and nonlinear components of the horizontal vestibuloocular reflex in squirrel monkeys.

Previous work in squirrel monkeys has demonstrated the presence of linear and nonlinear components to the horizontal vestibuloocular reflex (VOR) evoked by high-acceleration rotations. The nonlinear component is seen as a rise in gain with increasing velocity of rotation at frequencies more than 2 Hz (a velocity-dependent gain enhancement). We have shown that there are greater changes in the nonlinear than linear component of the response after spectacle-induced adaptation. The present study was conducted to determine if the two components of the response share a common adaptive process. The gain of the VOR, in the dark, to sinusoidal stimuli at 4 Hz (peak velocities: 20-150 degrees /s) and 10 Hz (peak velocities: 20 and 100 degrees /s) was measured pre- and postadaptation. Adaptation was induced over 4 h with x0.45 minimizing spectacles. Sum-of-sines stimuli were used to induce adaptation, and the parameters of the stimuli were adjusted to invoke only the linear or both linear and nonlinear components of the response. Preadaptation, there was a velocity-dependent gain enhancement at 4 and 10 Hz. In postadaptation with the paradigms that only recruited the linear component, there was a decrease in gain and a persistent velocity-dependent gain enhancement (indicating adaptation of only the linear component). After adaptation with the paradigm designed to recruit both the linear and nonlinear components, there was a decrease in gain and no velocity-dependent gain enhancement (indicating adaptation of both components). There were comparable changes in the response to steps of acceleration. We interpret these results to indicate that separate processes drive the adaptation of the linear and nonlinear components of the response.

Context-specific adaptation of saccade gain.

Previous studies established that vestibular reflexes can have two adapted states (e.g., gain) simultaneously, and that a context cue (e.g., vertical eye position) can switch between the two states. The present study examined this phenomenon of context-specific adaptationfor horizontal saccades, using a variety of contexts. Our overall goal was to assess the efficacy of different context cues in switching between adapted states. A standard double-step paradigm was used to adapt saccade gain. In each experiment, we asked for a simultaneous gain decrease in one context and gain increase in another context, and then determined if a change in the context would invoke switching between the adapted states. Horizontal eye position worked well as a context cue: saccades with the eyes deviated to the right could be made to have higher gains while saccades with the eyes deviated to the left could be made to have lower gains. Vertical eye position was less effective. This suggests that the more closely related a context cue is to the response being adapted, the more effective it is. Roll tilt of the head, and upright versus supine orientations, were somewhat effective in context switching; these paradigms contain orientation of gravity with respect to the head as part of the context.

Context-specific adaptation of saccade gain in parabolic flight.

Previous studies established that vestibular reflexes can have two adapted states (e.g., gains) simultaneously, and that a context cue (e.g., vertical eye position) can switch between the two states. Our earlier work demonstrated this phenomenon of context-specific adaptation for saccadic eye movements: we asked for gain decrease in one context state and gain increase in another context state, and then determined if a change in the context state would invoke switching between the adapted states. Horizontal and vertical eye position and head orientation could serve, to varying degrees, as cues for switching between two different saccade gains. In the present study, we asked whether gravity magnitude could serve as a context cue: saccade adaptation was performed during parabolic flight, which provides alternating levels of gravitoinertial force (0 g and 1.8 g). Results were less robust than those from ground experiments, but established that different saccade magnitudes could be associated with different gravity levels.