central vestibular dysfunction current literature and where to go from here
The term “central vestibular dysfunction” covers a broad range of pathologies, ranging from a single event such as a cerebellar stroke to chronic and fluctuant conditions such as vestibular migraine (Brown et al., 2006). A central vestibular disorder can be defined as a vestibular condition originating from problems with the brain and brainstem (Shepherd 2009). The challenge faced by clinicians providing assessment and treatment for these conditions centers around the diversity of root causes, severity, and progressive nature of some of the various central vestibular diagnoses, from concussion to multiple sclerosis.
Although patients with concussion can have peripheral vestibular issues as well, Skóra et al. (2018) found that at a 6 month follow-up in patients with mild traumatic brain injury (mTBI), more than half the patients still had abnormal VNG results that were indicative of a central vestibular dysfunction. Concussion Clinical Practice Guidelines, a joint effort between the Orthopedic, Sports, and Pediatric sections of the American Physical Therapy Association, were recently published in the Journal of Orthopaedic and Sports Physical Therapy in April 2020 (Quatman-Yates et al.). These guidelines provide comprehensive recommendations for assessment and treatment of concussion, taking into consideration the oculomotor, vestibular, autonomic, psychiatric, cervical, and cognitive symptoms that can be present in those with mTBI. Each case is unique, so the treatment should be individualized to provide guidance on graded return to aerobic exercise as well as addressing the individual deficits found on examination.
It is critical to provide proper monitoring and screening of those in the acute phase of concussion in particular, since the patients may not be aware of their own deficits. For example, in a 2019 study of 96 patients with acute mTBI (median age 38) by Marcus et al., researchers found that half of the patients had objective gait ataxia upon physical therapy assessment, even though these same patients denied any balance problems. Regarding prognosis, it is important to consider pre-existing conditions such as migraine and motion sensitivity. In one study on athletes with sports related concussion, it was discovered that a history of motion sensitivity was associated with a more prolonged vestibular dysfunction following mTBI (Sufrinko et al., 2019). If an individual already has challenges with increased sensitivity to sensory stimuli, this can result in a longer road to recovery from a central vestibular injury such as a concussion, which is important when determining a reasonable timeline for goal achievement in a course of physical therapy care.
Similar to concussion, a stroke in the brainstem or cerebellum can result with a presentation of central vestibular dysfunction. The good news is that there are at least a few studies that indicate that “a customized physical therapy intervention for stroke patients with brainstem injury who had vestibular symptoms identified significant improvement in postural control and functional activities” (Kwon and Ko, 2017). In addition, during a randomized controlled trial by Dai et al. (2013), researchers were able to train caregivers so that they could provide vestibular rehab exercise guidance and supervision to stroke patients with unilateral neglect. After 1 month of daily vestibular rehabilitation plus standard physical therapy, these patients had more improvements in ADLs and balance along with a reduction in neglect, as compared to standard physical therapy alone.
While it is encouraging that patients with cerebellar and brainstem stroke can improve with vestibular rehabilitation, diagnosis of such strokes can prove challenging at times. Imaging is not always reliable, since early MRI can result in a false negative. A three-step bedside oculomotor exam (H.I.N.T.S.: Head-Impulse—Nystagmus—Test-of-Skew) appears more sensitive for stroke than early MRI in acute vestibular syndrome (Kattah et al., 2009). In addition, the Subjective Visual Vertical bucket test can be useful in these cases where it is unclear whether a patient is having a stroke or a symptomatic vestibular migraine. Indeed, when used in conjunction with a focal neurological exam and clinical assessment for nystagmus, the SVV bucket test had a sensitivity of 92.6% and specificity of 88.9% when differentiating central vestibular dysfunction in stroke from vestibular migraine (Chang et al., 2019).
Like patients with cerebellar or brainstem stroke, those with vestibular migraine can benefit from physical therapy. A recent review by Alghadir and Anwer (2018) found that more randomized controlled trials are needed to confirm the benefits of vestibular rehabilitation for those with vestibular migraine. However, Whitney et al. (2000) and Vitkovic et al. (2013) both found that vestibular rehabilitation improved balance and reduced dizziness in patients with vestibular migraine. Collaboration between a physician and physical therapy can be beneficial since patient education, trigger management and reduction, and medication can all play important roles in improving the likelihood that a patient with vestibular migraine can tolerate and benefit from common vestibular rehabilitation techniques such as habituation to visual motion or self-movement (Knight, 2017). Interestingly, in children with migraine headaches (not diagnosed with vestibular migraine per se), a study by Baraldi et al. (2020) found evidence of a central alteration of vestibular pathways in these patients that makes balance function more visually dependent than healthy subjects, even between headaches. Key goals of vestibular rehabilitation in both adults and children with vestibular symptoms are often to gradually reduce visual dependence, improve balance, and increase habituation to sensory stimuli (Bogle 2019; Christy 2018). In addition, regular exercise seems to reduce migraine frequency, although ideal frequency and intensity of such exercise is unclear at this point (Amin et al., 2018).
While vestibular migraine is one of the most common central vestibular disorders, there can be malignant sources of central nystagmus seen during a vestibular exam. In fact, according to a study by Power et al. (2019), in 12% to 20% of cases, positional vertigo is due to CNS pathology, including cerebellar tumors. Power’s study followed three patients who required surgery (two for removal of a cerebellar tumor and one to address obstructive hydrocephalus), and in all three cases, the patients showed improvement in motion sensitivity and balance after a postoperative course of vestibular rehabilitation. Further research, particularly randomized controlled trials, would help to increase our understanding of the optimal frequency, duration, and types of activities that are best for rehabilitation in this patient population.
While cerebellar tumors and hydrocephalus can be life threatening, we can try to address them with surgery, but unfortunately degenerative and hereditary cerebellar ataxias are not treatable in this way. Patients with these types of cerebellar dizziness and imbalance benefit from a multimodal approach including physical and occupational therapy as well as medication to reduce presenting symptoms (Zwergal et al., 2020). Even worse, some of these degenerative conditions affect both the central vestibular pathways as well as resulting in bilateral peripheral vestibular loss (Pothier et al., 2012). In these cases, the focus of physical therapy should go beyond vestibular rehabilitation and ensure adequate attention to balance training, safe mobility, assistive equipment and home safety planning, assessment for benefit from balance-based torso weighting, and patient and family education and training, in addition to concurrent medical monitoring and management.
Progressive neurologic diseases beyond cerebellar ataxia can also impact the vestibular system and may benefit from vestibular rehabilitation and assessment. For example, Tramontano et al. (2018) found that a four week course of vestibular rehabilitation in patients with severe multiple sclerosis reduced fatigue and improved balance and activities of daily living. Similarly, a study in patients with Parkinson’s disease found that eight weeks of customized vestibular rehabilitation resulted in significant balance improvements (Acarer et al., 2015). This may relate to the fact that there is limited but increasing evidence that VEMPs, in particular, are abnormal in patients with Parkinson’s disease (Smith 2018). From an assessment perspective, Nakamagoe et al. (2019) found that in patients with amyotrophic lateral sclerosis (ALS), the reduced ability to use visual fixation to suppress nystagmus (induced by caloric testing) correlates with decreased frontal assessment battery scores (test for executive function). Therefore, a simple vestibular function test could potentially provide a means to objectively monitor cerebral ALS lesions.
The vestibular system connects to the muscles of our eyes, trunk, and limbs via specific brainstem and cerebellar structures, so disruption of these neural pathways can result in vertigo, imbalance, nystagmus, and other neurological signs (Lea and Pothier, 2019). Such an elegant neurological network is vulnerable to trauma, disruptions in blood flow, genetic and progressive disease, and complex impaired functional presentations such as what is seen in patients with migraine. However, with this complexity comes opportunities for new and different neural pathways to form and adaptations to develop. The desire to tap into this neuroplasticity is the driving force for patient and clinician efforts in physical therapy for those with central vestibular dysfunction. The heterogeneity of presentation even within each central vestibular diagnosis is a challenge to the ability of clinicians to adapt and individualize their treatments, using clinical evidence whenever it is available to improve decision making and optimize patient outcomes. No matter how complex, every patient matters, and so we look forward to further research to support the care of those with central vestibular dysfunctions.
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