Vestibular Disorders

Vestibular disorders refer to a group of problems affecting an individual's sense of balance. Dizziness, vertigo, unsteadiness, light-headedness, and disequilibrium are some of the words people may use to describe a feeling of imbalance. Most vestibular disorders are transient and improve with observation and occasional symptomatic treatment. However, in rare instances, imbalance can be a sign of a potentially serious disorder.

The vestibular system is composed of a set of balance organs within each inner ear (collectively referred to as the labyrinth), nerves connecting the labyrinth to the brain, and various nuclei within the brainstem, cerebellum, and cerebral cortex that interconnect at multiple levels. The brain uses the input from both labyrinths to help determine one's position in space. If there is a disturbance in input from one side, the asymmetry may be perceived as imbalance. Vision, proprioception (the ability to sense one's position in space with the eyes closed), and central integration (the processing by the brain of input from the eyes, ears, head, trunk, and extremities into a meaningful whole) also significantly influence balance and are considered part of the vestibular system.

In addressing complaints of dizziness, physicians must first consider whether symptoms arise from true vestibular dysfunction or from a more general medical cause. Diabetes, cardiac arrhythmia, and hypotension are some of the many disorders that can cause dizziness or exacerbate a true vestibular disorder. Complaints of frank vertigo (the illusion of a turning motion) or the presence of nystagmus (an involuntary linear or rotary movement of the eye) on physical exam denote a vestibular problem. Once a vestibular lesion is suspected, a distinction is then made as to whether the site of the lesion is inside the brain or brainstem (central) or outside (peripheral). The pattern of onset (acute, subacute, progressive, intermittent), the duration of dizziness (seconds, minutes, hours, days), and associated signs and symptoms (hearing loss, tinnitus, head trauma) can further help to localize the lesion.

The diagnosis of most vestibular disorders is through a careful history and physical exam. A neurological exam is essential to identify disturbances in gait and balance and to uncover the presence of cranial nerve neuropathies, which may help to localize a lesion. The head-and-neck exam is focused on identifying the presence and direction of nystagmus and ruling out evidence of otologic pathology (a draining ear, mass, membrane perforation), which may suggest the cause of the problem. Once a differential diagnosis is established, additional testing such as an [Page 1601]electronystagmogram (ENG) can then help to rule in or out a specific diagnosis.

Vestibular dysfunction can be caused by vascular events (migraine, stroke, hypotension), infections (labyrinthitis, otitis, mastoiditis), trauma to the temporal bone, autoimmune disorders (Cogan syndrome), metabolic derangements (diabetes, hypothyroidism), or neoplasms (vestibular schwannomas). Some diseases are idiopathic, such as benign positional vertigo (BPV) and Meniere's disease. Common peripheral vestibular disorders include BPV, Meniere's disease, vestibular neuronitis, acoustic neuromas, and labyrinthitis. Central vestibular disorders include migraine, multiple sclerosis, vascular insufficiency, cerebellar dysfunction, and Arnold-Chiari malformation, among others.