Chronic Dizziness and Postural Instability

Dizziness is a vague term describing various sensations, including a subjective feeling of uncertainty, postural instability, or motion in space. It also encompasses other sensations (eg, light-headedness, wooziness, near fainting). The elderly often use the term even more broadly to include weakness, fatigue, and myriad other symptoms. Dizziness can be classified, somewhat arbitrarily, as acute (present for < 1 month) or chronic (present for > 1 month). Because the causes, diagnosis, and treatment of acute dizziness are similar for all adults, this chapter discusses only chronic dizziness and postural instability. The prevalence of chronic dizziness among the elderly ranges from 13 to 30%.

Dizziness is divided by history of sensation into five categories: (1) vertigo: a rotary motion, either of the patient with respect to the environment (subjective vertigo) or of the environment with respect to the patient (objective vertigo), the key element being the perception of motion; (2) dysequilibrium (unsteadiness, imbalance, gait disturbance): a feeling (primarily involving the trunk and lower extremities rather than the head) that a fall is imminent; (3) presyncope (faintness, lightheadedness): a feeling that loss of consciousness is imminent; (4) mixed dizziness: a combination of two or more of the above types; and (5) nonspecific dizziness: a sensation of instability that does not fit readily into any of the previous categories.

In the standard clinical approach, dizziness is considered a symptom of one or more discrete diseases. It is further assumed that the categories of dizziness correspond to diseases within specific systems (eg, vestibular, proprioceptive, cardiovascular). These assumptions work well for younger patients and for patients of all ages with acute dizziness. However, among elderly patients with chronic dizziness, the relationship between categories and specific systems or etiologies is less consistent. Using the standard approach, many elderly patients with chronic dizziness are left undiagnosed (and untreated), or the diagnoses made by physicians from different specialties are variable and inconsistent. For these reasons, chronic dizziness might better be considered a geriatric syndrome--a condition resulting from multiple diseases and impairments--rather than solely a symptom of discrete diseases.

Etiology and Pathophysiology

Although the reported prevalence for specific causes varies widely, the most commonly reported discrete disorders causing chronic dizziness include peripheral vestibular disorders (eg, benign paroxysmal positional vertigo, neurolabyrinthitis, Meniere's disease); cervical disorders, particularly spondylosis; cerebrovascular disorders, including vertebrobasilar insufficiency and brain stem infarcts; carotid hypersensitivity; and psychiatric disorders, particularly depression and anxiety (see Table 19-1).

Chronic dizziness and postural instability most often result from the combined effects of disorders and impairments in the multiple systems contributing to stability and equilibrium. The sensation of equilibrium requires input from complex networks of sensory, motor, and central integrative neurologic systems. These systems are, in turn, influenced by cardiovascular, respiratory, metabolic, and psychologic factors. Chronic dizziness may occur when there is overwhelming dysfunction of one system or, probably more often, when there is impairment or dysfunction within several systems.

The visual, auditory, vestibular, and proprioceptive systems are responsible for orienting a person in space. These systems interact and can have multiple interconnections. Age-related visual changes include decreased acuity, adaptation to darkness, sensitivity to contrast, and accommodation. In addition, ocular diseases, including macular degeneration, glaucoma, and cataracts, are common. Hearing contributes directly to stability through detection and interpretation of auditory stimuli, which help localize and orient a person in space, especially when other senses are impaired. Decreased hearing is also often a marker of vestibular dysfunction, which is difficult to test clinically.

The vestibular system (see Figure 19-1) contributes to spatial orientation at rest and during acceleration and deceleration and is responsible for visual fixation during head and body movements. Age-related decline in vestibular function can be due to changes in the otoconia (tiny calciferous granules that form part of the receptor mechanism in the otolith apparatus), perhaps due to osteoporosis or saccular degeneration. Benign paroxysmal positional vertigo (see Table 19-1 and Figure 19-2) is thought to result from changes in the otoconia.

The vestibular nerve, which connects the vestibular system to the central nervous system (CNS), is particularly sensitive to hypoglycemia and drugs (aminoglycosides, aspirin, furosemide, quinine, quinidine, and perhaps tobacco and alcohol). Head trauma, mastoid or ear surgery, and middle ear infections may also damage the vestibular nerve.

The proprioceptive system (comprised of peripheral nerves, the mechanoreceptors located in apophyseal joints, the posterior columns in the spinal cord, and multiple CNS connections) orients a person in space during position changes and while walking on uneven surfaces. Abnormalities in any component of the system may cause or exacerbate dysequilibrium. Whether age-related changes occur in peripheral nerves is unknown, although peripheral neuropathy is common in the elderly, especially from diabetes or vitamin B₁₂ deficiency.

The contribution of cervical mechanoreceptors to proprioception is not widely appreciated. The loss of normal afferent input from mechanoreceptors may result in a disturbance of postural sensation (sense of balance) and of kinesthesia (awareness of head and neck movement), on which precise control of voluntary movements such as walking depend. Whiplash injuries and cervical degenerative diseases (eg, spondylosis) may impair functioning of the cervical mechanoreceptors.

The CNS channels input data from the senses to the appropriate efferents in the musculoskeletal system. Given the multiple connections and their complexity, essentially any CNS disorder may contribute to instability or dizziness.

Systemic disorders may contribute to instability or dizziness by affecting the sensory, central, or effector components. In addition, systemic disorders may result in decreased cerebral perfusion or oxygen delivery, fatigue, confusion, or shortness of breath, which, in turn, may result in instability or dizziness. Common examples include electrolyte disorders, anemia, hypothyroidism, and acid-base disturbances. Cardiac arrhythmias or heart failure may compromise cerebral blood flow. Drugs may cause dizziness through several mechanisms, including postural hypotension, fatigue, dehydration, electrolyte disturbance, and disruption of CNS function.

Diagnosis

Diagnosis is best begun by considering, based on history and examination, whether a single cause (see Table 19-1) is likely, in which case specific diagnostic testing is warranted. If the history and examination do not suggest a specific cause, it is unlikely that exhaustive diagnostic testing will be helpful. The goal in most patients, therefore, is to identify and eliminate or ameliorate as many contributing factors as possible (see Table 19-2). This approach is based on the following assumptions: (1) the relative importance of individual contributors to dizziness often cannot be determined; (2) the presentation often does not permit identification of a specific cause, thus therapeutic trials are often the best way to determine significant contributors; and (3) ameliorating even a subset of contributors may reduce the dizziness.

History: The patient should be asked to describe the nature of the dizziness, including sensation, frequency and duration, any associated symptoms, any precipitating or provoking factors, and any predisposing exposures and diseases (see Table 19-2). However, patients often report more than one manifestation or a vague sensation. The patient should be screened for depression and anxiety, which may provoke or exacerbate the dizziness. A thorough review of all drugs, including over-the-counter drugs (especially hypnotics, analgesics, and drugs used for colds and allergies), is also important.

Physical examination: Useful findings of the physical examination are listed in Table 19-2. Vestibular system abnormalities are difficult to detect clinically. The examiner should look for nystagmus occurring spontaneously or in response to changes in eye or body position. Because visual fixation can suppress nystagmus, Frenzel glasses (high-diopter lenses in a frame with a light source) are used if available. Two other methods of detecting vestibular dysfunction are checking visual acuity during head shaking and testing balance (eg, one leg or tandem stand) while standing on thick foam with eyes closed. However, the sensitivity and specificity of these two tests have not been determined.

Blood pressure and heart rate measurements should be taken after at least 5 minutes of quiet lying and then at 0 and 2 minutes after standing. A change of >= 20% in mean postural blood pressure is most significant.

Neck range of motion, preferably in a standing position, should be determined. Decreased range of motion--with or without symptoms of dizziness or unsteadiness--may be due to a cervical process or, secondarily, to vestibular dysfunction (the sensation of dizziness on head turning can lead to decreased range of motion secondary to prolonged neck immobilization). Decreased head turning can interfere with central compensation; recognizing it is important because vestibular rehabilitation is helpful.

Balance and gait should be evaluated, although most findings are nonspecific. On testing, a performance that is poorer with eyes closed than with eyes open suggests a vestibular or proprioceptive problem. A steppage gait suggests proprioceptive deficits, as does an improvement in gait when the patient touches his fingertip to the examiner's fingertip. Vibratory testing is more sensitive than position sense testing for assessing proprioception.

Provocative tests: Attempts can be made to induce dizziness through various maneuvers. Hyperventilation is not particularly helpful because it may induce dizziness in many elderly patients, with or without a history of chronic dizziness. The Hallpike maneuver involves a rapid change in position from seated to supine with the head hanging 45° to the right or left (see Figure 19-3). The occurrence of nystagmus (and often vertigo), which lasts 10 to 30 seconds, after a few seconds of latency indicates a positive response. A positive response in any of the head positions confirms the suspected diagnosis of benign paroxysmal positional vertigo.

Laboratory evaluation and specialized testing: A CBC, thyroid function tests, and glucose and vitamin B₁₂ levels should be obtained for all elderly persons presenting with chronic dizziness. Indications for ECG, Holter monitoring, carotid sinus massage, and tilt table testing are discussed in Ch. 18. However, abnormal findings are common among elderly patients with or without dizziness, and abnormal results may or may not correspond to the complaint of dizziness in this age group. Cerebral CT or MRI should be performed only if the history and physical examination suggest a cerebral lesion. Audiometry is useful in identifying the severity and type of hearing loss; specific findings may also indicate Meniere's disease or acoustic neuroma.

Vestibular testing, including caloric testing, electronystagmography, rotational testing, and computerized posturography, can be considered in patients with history or physical examination findings suggestive of vestibular disease.

Caloric testing assesses the symmetry of vestibular function. Each ear is stimulated with 250 mL of first warm (44° C [111° F]) and then cool (30° C [86° F]) water, each instilled over 40 seconds. The ear that shows a shorter duration or lower frequency of nystagmus is presumed to be the diseased ear.

Rotational testing uses a series of well-controlled rotational stimuli to provoke nystagmus. Findings can reveal the degree of peripheral or central vestibular dysfunction; serial measurements can be used to detect worsening of the dysfunction.

Electronystagmography, in which eye movements are recorded on an ECG-like tracing from electrodes placed around the eyes, is used to observe vestibular nystagmus during provocative testing.

In computerized posturography, the patient stands on a platform that is imbedded with four sensors to monitor sway. Testing with the eyes closed or with a moving screen while the platform is synchronized to patient movement eliminates visual and proprioceptive information. This approach examines balance that is principally dependent on vestibular input. Other testing combinations examine visual and proprioceptive inputs to balance. Functional deficits defined by posturography can thus indicate visual, proprioceptive, or vestibular deficits, which require further testing to determine specific diagnoses.

Prognosis and Treatment

Although chronic dizziness may be a symptom of significant disease, it does not per se increase the risk of death. However, it does have adverse physical, psychologic, and social consequences. It increases the risk of falls and fear of falling, decreases performance in activities of daily living, and reduces participation in social activities. The primary goal of treatment is to reduce dizziness sufficiently to minimize the physical, psychologic, and social morbidity.

Treatment is ideally directed toward a specific cause. However, because the etiology is usually multifactorial, the most effective treatment is often to ameliorate one or more contributing factors (see Table 19-1). Even partial amelioration of the dizziness may help. Because adverse drug effects may contribute to many cases of chronic dizziness, attempts should be made to eliminate as many drugs as possible, to substitute less offending ones, or to reduce the doses.

Drugs: Vestibular depressants (eg, meclizine, diazepam) have little role in the treatment of chronic dizziness. Because of their effects on the CNS and because they may suppress central adaptation, these drugs may even exacerbate dizziness. However, patients with severe unilateral peripheral vestibular dysfunction may benefit from a benzodiazepine.

Rehabilitation and exercise: Vestibular rehabilitation includes combinations of exercises involving head and eye movements while sitting or standing. It also involves various dynamic balance exercises and exercises to improve gait stability during head movement, visual and vestibular interactions, and vestibular spinal responses. Initially, the exercises may worsen the dizziness, but over time (weeks to months) movement-related dizziness improves, likely because of central adaptation. Vestibular rehabilitation has been shown to be effective in most vestibular disorders of central or peripheral origin. Vestibular rehabilitation can be administered in a classroom setting or one to one with a physical therapist. Alternatively, patients can perform the exercises independently at home after being instructed by a physical therapist, who must ensure that the patient can adhere to the program safely and effectively.

Cervical exercises may be effective for patients with cervical spondylosis. Progressive, competency-based balance exercises have proved effective at enhancing the sense of stability and may be useful for patients with dizziness related to sensory and/or motor deficits. When proprioception is impaired, the use of a cane is indicated to provide stability.

Patient education: Patients should be reminded to avoid over-the-counter drugs that may exacerbate dizziness. If postural hypotension is identified, patients should be instructed to rise slowly (the time required for stabilization varies from a few seconds to several minutes). Hand clenching and ankle dorsiflexion exercises performed before standing and the use of support stockings may also help. These patients should also be taught to avoid hot showers or baths and to reduce salt restriction in situations that might lead to dehydration (eg, hot weather, diarrhea, vomiting).

Patients should be instructed on which activities to avoid. Movements such as looking up, reaching up, or bending down are to be avoided, in part by storing items at home strategically. However, patients should be cautioned not to habitually avoid other movements, such as head turning. Avoiding these movements may compromise central adaptation, thereby exacerbating dizziness.