OVERVIEW OF VESTIBULAR DYSFUNCTION
Dizziness is a common complaint among adults aged 18 years and older (Kerber et al., 2017). The incidence of dizziness rises with advancing age, with 20% to 35% of persons over age 65 reporting problems with dizziness in the previous 12 months (Lin & Bhattacharyya, 2012; Tinetti et al., 2000). Symptoms of dizziness can have a catastrophic impact on wellness, often leading to unsteadiness with walking and increased incidences of falls and associated injuries. Persons experiencing difficulties with balance due to dizziness can develop a fear of falling, and subsequently reduce their mobility and participation in activities (Vellas et al., 1987), with as many as 56% of older adults restricting activities due to this fear (Howland et al., 1998). A systematic review of studies identifying the etiology of dizziness in the adult population revealed vestibulopathy, cardiovascular dysfunction, central nervous system (CNS) dysfunction or lesion, psychiatric, and other medical disorders (e.g., metabolic, polypharmacy) as the primary diagnostic classifications (Kroenke et al., 2000). Of these, dizziness was attributed to peripheral vestibulopathy in 44% of the patients studied. Vestibular dysfunction affects 35% of adults over age 40, with the incidence rising to as much as 85% for persons 80 years of age and older (Agrawal et al., 2009). Hallmark symptoms of vestibular dysfunction are vertigo, dizziness, nausea, oscillopsia, and imbalance, which are the primary reasons for seeking medical care. Vertigo is the illusion of self-motion or object motion in a rotational manner, which the patient often describes as “spinning.” Patients with vestibular dysfunction can also report changes in cognition and a sense of feeling “foggy” or experiencing “brain fog.” Taken together, the consequences of these symptoms can have a profound negative impact on the patient’s state of physical, social, and emotional well-being. Data from the U.S. National Health Interview Survey revealed the enormity of the impact on quality of life for individuals experiencing problems with dizziness and balance limitations (Lin & Bhattacharyya, 2012). Of the seven million persons surveyed, 61% reported not participating in their usual physical activities, 45% did not participate in social activities, and one quarter required assistance with self-care and activities of daily living due to problems with their balance. Thus, in addition to the risk of injurious falls, there is a potentially dramatic impact on loss of independence and a subsequent emotional toll that ensues in
persons with vestibular dysfunction, necessitating early diagnosis and effective management to reduce the decline in quality of life. Of those individuals seeking care for their balance problems, the vast majority saw a general practitioner, neurologist, or cardiologist, 16% saw an otolaryngologist, and nearly 3% sought chiropractic care (Lin & Bhattacharyya, 2012). Recent data from the National Medical Ambulatory Care Survey demonstrates a growing prevalence of ambulatory care visits for BPPV, with twice as many visits seen with primary care than neurology (Dunlap et al., 2018). Despite clinical practice guidelines published by the American Academy of Otolaryngology – Head and Neck Surgery Foundation that supports vestibular rehabilitation and avoidance of antivertigo or antiemetic medications, these medications were found to have been prescribed in more 20% of primary care visits (Bhattacharyya et al., 2017), while referral to physical therapy services for rehabilitation of peripheral vestibular disorders remained low (Dunlap et al., 2020). The source of dizziness complaints is not always easy to identify; it can range from polypharmacy to cardiac dysfunction to neurological disorders or to vestibular pathology. Effective diagnosis and management of balance disorders require detailed knowledge of the systems that mediate postural control, which includes the vestibular system. When peripheral vestibular dysfunction is the source of dizziness and balance limitations, as is true in nearly half of the cases, pharmacological or surgical management is not typically warranted. Rather, most cases of peripheral vestibular dysfunction require rehabilitative care to facilitate CNS compensation for the loss of vestibular function or to address the mechanical basis for the altered function. Compensation refers to the resolution of those symptoms associated with vestibular dysfunction, such as vertigo, nausea, and imbalance, despite permanent loss or damage to peripheral structures noted on objective tests (Herdman & Clendaniel, 2014). Given the vast numbers of individuals afflicted with peripheral vestibular disorders with resulting movement dysfunction, and that best practice dictates a focus on a problem-oriented treatment approach, physical therapists are well positioned as the practitioner of choice to address the needs of this population.
FUNCTIONAL AND STRUCTURAL ANATOMY OF THE VESTIBULAR SYSTEM
The vestibular system is a highly specialized sensory apparatus that is responsible for detecting head motion and position relative to gravity. Information from the vestibular end organs is integrated with sensory information from the visual and somatosensory systems in the CNS to generate compensatory movements in order to maintain head and body postural stability and head-eye coordination to stabilize gaze. The anatomy of the vestibular system is composed of a peripheral portion, which includes the three semicircular canals, the two otolith organs, and the vestibulo-cochlear nerve (CN VIII), and a central Peripheral vestibular structures The peripheral vestibular system lies within the labyrinth of the inner ear and is composed of a bony and a membranous component (see Resources section for link to anatomy). The bony labyrinth contains two main structures, the cochlea and the semicircular canals, which are adjoined by the vestibule. The membranous labyrinth lies within the bony labyrinth and is suspended by connective tissue and perilymphatic fluid, which is similar in chemical nature to cerebrospinal fluid (see Figure 1). Within this membranous structure is the membranous portion of the semicircular canals and the two otolith structures, named the utricle and saccule. Within the membranous labyrinth is endolymphatic fluid, which is similar to intracellular fluid in its composition.
portion that includes the vestibular nuclei and the cerebellum. Motor output from the vestibular system is mediated by the vestibulo-ocular and vestibulospinal white-matter tracts. The vestibulo- ocular pathway sends information regarding linear and angular head motion to the extra- ocular muscles to mediate gaze stabilization during movement. The vestibulospinal tract carries information to the skeletal muscles to drive compensatory antigravity balance reactions in response to head position changes. Semicircular canals The semicircular canals and otoliths are the motion sensors of the vestibular system, detecting angular head motion. The three semicircular canals are oriented in orthogonal planes, which means that they lie at 90° angles from one another, and are named for their relative location in the inner ear: anterior, posterior, and horizontal, also known as superior , inferior , and lateral , respectively (see Figure 1). Both ends of the semicircular canals are contiguous with the vestibule, with one end widened in a bulbous fashion, referred to as the ampulla. The ampullae serve an important anatomic role; they house the mechanoreceptors for the semicircular canals and create a barrier between the canal and vestibule. This configuration is the basis for the translation of head movement
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