Unravelling Risk Factors for Chronic Dizziness in Patients After an Acute Unilateral Vestibular Deafferentiation.

In humans, acute unilateral peripheral vestibular dysfunction, whether by disease, accident, toxicity or iatrogenic, produces the unilateral vestibular deafferentiation (uVD) syndrome. In many patients, it resolves spontaneously and more or less completely because of central compensation. However, more detailed observations have revealed that 29-66% of uVD patients develop disabling chronic dizziness that lasts more than 1 year after the acute event, irrespective of the underlying etiology and regardless of the way the chronic complaints are documented: clinical bedside tests, vestibulo-ocular reflex(VOR) measurements, balance performance or perceived handicap. Although these chronic symptoms are not severe or life-threatening, they generate significant personal and social handicap in patients, leading to frequent consultations in general practice, Ear-Nose-Throat(ENT) and neurology clinics. A recent epidemiologic study revealed a prevalence of 6.5% of peripheral vestibular disorders in 70.315.919 patients in Germany thereby demonstrating its impact on society in a developed country. Identifying predictors of the "acute-to-chronic" dizziness transition would allow patients at high risk for developing chronic dizziness to be targeted with personalized therapies to reduce healthcare costs. In addition, up to 50% of patients with a chronic vestibular syndrome have a risk of developing depression or anxiety disorders. Therefore, the main objective of this study is to identify predictors of chronicity with a focus on investigating the effect of patients' tendency to avoid complaint-triggering movements and the actual level of physical activity on long-term outcomes in patients after acute uVD. Medical treatment in the acute phase is currently focused on symptomatic treatment with antivertiginous drugs (antihistamines) while motivating and helping patients to move as quickly as possible, an essential part of vestibular rehabilitation. There is moderate to strong evidence that vestibular rehabilitation is a safe, effective management for unilateral peripheral vestibular dysfunction, based on a number of high-quality randomized controlled trials. Furthermore, there is moderate evidence that vestibular rehabilitation resolves symptoms and improves functioning in the intermediate term but there is insufficient evidence to discriminate between different forms of vestibular rehabilitation. Based on a clinical practice guideline from the American Physical Therapy Association (Neurology Section),clinicians may offer specific exercise techniques to target identified impairments or functional limitations and may provide supervised vestibular rehabilitation. Despite the consensus on the usefulness of physical therapy, incorporation of physical therapy programs in daily management of patients after acute uVD remains troublesome. Research into health care utilization in patients with dizziness revealed a low number of visits for vestibular disorders were referred to physical therapy in ambulatory care. Moreover, the confrontation with current practice and the review of research protocols that study long-term outcome after an acute uVD show that the approach usually consists of encouraging patients to move a round as much as possible without the supervision of the physical therapist. Early and active vestibular rehabilitation is crucial. However, there are no known studies that investigate the actual physical activity level and/or exercise adherence in home exercise programs in patients with acute uVD. Therefore, our first objective is to study the effect of physical activity/movement volume in the acute stage on long term outcome after an acute uVD. Furthermore, psychological factors such as anxiety, depression and fear of falling have a negative effect on the outcome of vestibular rehabilitation. Indeed, recent data show that long-term prognosis in vestibular neuritis patients is more linked to anxiety and somatization traits than to objective vestibular findings. Pathophysiologic processes seem to include precipitating events that trigger anxiety-related changes in postural strategies with an increased attention to head and body motion and a cocontraction of leg muscles. Fear of movement in response to injury is a concept first introduced in the field of chronic low back pain, where it was shown that fear of inducing or increasing pain could lead to a maladaptive response of restricting movements and activities. In contrast, the confrontation response leads to increased movement and return to activities. This model can be translated to vestibular disorders as avoiding complaint-inducing movements is a known compensation strategy used by patients with an acute uVD. These physical activities are very important to promote compensation and avoiding them can therefore contribute to greater disability. Therefore, the second objective is to study the effect of activities avoidance behavior on long term outcome after an acute uVD. Acute uVD is defined by the patient history, the clinical examination and often characterized by measurable vestibular parameters using three-dimensional video head impulse testing (vHIT), caloric irrigation, sinusoidal harmonious acceleration testing (SHA) and cervical/ocular vestibular-evoked myogenic potentials (c/o VEMP). However, whether these VOR function measurements can predict chronicity is questioned. Recently a new tool (i.e. the Perez and Rey (PR) score) was developed to characterize the state of vestibular compensation of subjects diagnosed with acute uVD of peripheral origin. The PR score is a measure of temporal organization of the refixation saccades that enables to distinguish clearly and objectively between subjects that are in a compensated or uncompensated vestibular situation. However the PR score has never been studied as a prognostic factor of progression to chronicity. Therefore, the third objective is to study the effect of early central vestibular compensation as measured by the PR score on long term outcome after an acute uVD. Accurate perception of gravity is important for spatial orientation, postural balance, and the regulation of gait. Multiple sensory signals contribute to the central processing of this percept, including signals from visual, vestibular and somatosensory systems. Patients after an acute uVD suffer from a deteriorated sense of spatial orientation, leading to balance problems. In uncompensated vestibular patients the remaining sensory cues will need to compensate for the loss of vestibular information. Recently a reweighting of sensory signals with an increase in visual weight of 20-40% was suggested in patients with a bilateral vestibular function loss. This visual compensation strategy can make some patients dependent of stable visual cues which might lead to visual motion sensitivity. Evidence is mounting that visual field dependency is also a factor contributing to visual vertigo in patients with vestibular disorders. Visually induced dizziness or visual vertigo is a specific form of persistent perceptual postural dizziness which is classified as a chronic functional vestibular disorder. Therefore, the fourth objective is to study the effect of visual motion sensitivity on long term outcome after an acute uVD.