Dizziness in the Elderly

Introduction

Dizziness is a broad term used to describe a variety of sensations such as vertigo, unsteadiness, imbalance, light-headedness, and similar symptoms. The prevalence of dizziness increases steadily with age. Although debate is still ongoing regarding the underlying causes of this increase in prevalence, there is universal agreement on the devastating consequences and high physical, cognitive, emotional, and financial toll of dizziness and imbalance on the older population. Taken together, the impact of dizziness on the quality of life in older patients is profound.

It is estimated that one-fourth to one-third of the population older than 65 years has experienced some form of dizziness. This range in the reported prevalence rates reflects differences across the series in the cutoff age of participants, type(s) of symptoms for inclusion, duration and frequency of symptoms, and whether the sample was taken from community-dwelling patients, primary care facilities, or specialty clinics. In the older than 85 years age-group, the number of adults with dizziness increases to about 50%. The prevalence of these symptoms seems to be greater for women.

It is important to recognize that older dizzy patients typically present with a different symptom profile compared to their younger counterparts. Younger patients more often complain of true vertigo, nausea, and emesis, whereas older patients more often report symptoms of unsteadiness, imbalance, and disequilibrium.

Older individuals who suffer from dizziness are at a significantly higher risk of accidental falls and consequent injuries. It is estimated that approximately 30% of adults older than 65 years will fall at least once, and roughly 50% of those will fall again. The consequences of such falls are devastating. Falls are the leading cause of accidental death in people older than 65 years, and non-fatal falls are the main reason for hospital admissions in this age-group. Fall-related injuries can lead to mobility restrictions, loss of independence, and even confinement to nursing facilities. In addition to the physical and emotional cost, these injuries also carry a heavy financial burden, estimated at over $19 billion in direct costs in the year 2000 and rising steadily since.

A number of studies have established that for older adults, a history of dizziness or imbalance is an independent risk factor for falling ; however, the association between the two has not been as strong in other studies. This is not surprising as falls are complex phenomena involving neurologic, biomechanical, and other factors; therefore, fall risk factors can be heavily influenced by study design and patient selection methods. Rubenstein and Josephson used a meta-analysis of 12 large studies and found that balance disorders and dizziness were the second and third leading causes of falls in older persons, respectively. Vertigo, unsteadiness, and related symptoms also have an indirect effect on falls. It is well established that these symptoms in older individuals lead to the fear of falling. In turn, the fear of falling is considered a strong predictor for those who will suffer one or more actual falls.

The general topic of falls is beyond the scope of this chapter. However, the strong association between falls and symptoms of dizziness and imbalance highlights the importance of understanding the causes of these symptoms and devising effective methods for managing them in the older population.

Causes of Dizziness and Disequilibrium in Older Individuals

A substantial body of research demonstrates that the symptom of dizziness stems from a heterogeneous collection of underlying factors and is often multifactorial. In some studies, no specific etiology could be identified to explain the symptoms of a large subset of the subjects. The term presbystasis is used to describe this type of age-related disequilibrium that cannot be attributed to any known pathology. On the other hand, other studies have been able to assign one or more diagnostic categories to the majority of elderly patients suffering from dizziness. These discrepancies have led some investigators to suggest that dizziness in the elderly should be viewed as a multifactorial geriatric syndrome involving many different symptoms and originating from many different systems, such as sensory, motor, vestibular, neurologic, cardiovascular, and other systems.

The underlying causes of dizziness and disequilibrium in older adults can be divided into three broad categories:

1.
Age-related decline of acuity in sensory and motor pathways as well as deterioration of integration mechanisms within the central nervous system (CNS). Loss of hair cells in the labyrinth is an example of an age-related change in the sensory system. These types of losses are considered a normal part of aging because they are so common in older adults. However, they are most likely caused by subtle pathologies accumulated over a lifetime (e.g., ischemia) that are highly prevalent in the elderly.
2.
Pathologies that cause dizziness in any age-group, which become more prevalent in older individuals, either because age-related changes noted earlier make the elderly more susceptible to these pathologies or because the cumulative probability of exposure to these pathologies increases with time. An example of such pathology is benign paroxysmal positional vertigo (BPPV) that can occur at any age but is more common in the elderly, likely because of the ongoing deterioration of the maculae of the otolith organs.
3.
An assortment of environmental and lifestyle factors that increases the chance of dizziness and balance problems in the elderly. One such example is polypharmacy in the elderly, with many medications having the common side effect of dizziness (see Chapter 18 ).

A different type of classification is often used to divide risk factors for falls. This classification involves causes that are intrinsic to the patient versus those that are extrinsic. For dizziness and balance problems, such a classification is more relevant when considering appropriate intervention methods, which will be discussed later in this chapter. Here, each of the aforementioned three categories will be discussed in detail.

Age-Related Deterioration of Sensory and Motor Mechanisms

Human balance function depends on coordinated streams of sensory input from the vestibular, proprioceptive, and visual systems as well as proper integration of those inputs in the CNS. Furthermore, movement control requires the motor centers to accurately process sensory information and transmit the necessary commands to the appropriate muscles. Both structural and functional deteriorations in all of the aforementioned systems are known to occur with advancing age.

Vestibular system

Age-related loss of hair cells has been documented within the cristae ampullares of the semicircular canals and the maculae of the saccule and utricle. Earlier studies had indicated greater loss of hair cells in the semicircular canals and saccule and a higher proportion of loss for type I versus type II hair cells. More recent studies have used a counting method that is deemed to be less biased. These studies have confirmed the age-related loss of hair cells in the labyrinth, although the affected sites and type of hair cells have differed somewhat from previous studies.

Structural integrity of the vestibular nerve is also affected by age. The number of primary vestibular neurons within Scarpa’s ganglion has been shown to decline by approximately 25% over the life span. Similarly, the study of brainstem specimens in different age-groups has demonstrated a decrease in the number of secondary vestibular neurons within the vestibular nuclei.

Age-related degeneration of peripheral and central vestibular structures is similar to that of the auditory system and is most likely caused by subtle changes of blood flow to the inner ear. Microvascular changes with aging have been reported in both human and animal studies. Any decrease in blood flow to inner ear structures can have profound effects because inner ear arteries lack anastomotic connections.

Age-related changes of vestibular structures have been objectively confirmed by vestibular function tests. For example, both longitudinal and cross-sectional studies have shown an age-related decrease in vestibulo-ocular reflex (VOR) gain during sinusoidal rotation. This finding indicates that, unlike pathologies that usually affect only one labyrinth, age-related changes of vestibular pathways are more likely to mimic bilateral reduction of function. In addition, phase lead for low frequency sinusoidal stimuli and short vestibular time constants for step stimuli have been reported in older subjects. These findings are consistent with deterioration of the velocity storage mechanism within the brainstem. Similar degradation of central vestibular pathways has been demonstrated for otolith-ocular responses during off-vertical axis rotation.

Despite the overwhelming evidence in support of age-related changes of peripheral and central vestibular structures, the relationship between those changes and dizziness or disequilibrium in the elderly is not necessarily linear. Several studies have demonstrated high prevalence of vestibular impairment in elderly individuals. However, once patients with specific vestibular pathologies are removed from the sample, the contribution of age-related vestibular decline to balance impairment in the elderly is not as profound. Clearly, additional research is needed to examine the association of age-related changes in the vestibular pathways in older adults with symptoms of dizziness and disequilibrium.

Proprioceptive system

Proprioceptive sensors reside in the muscles, joints, and tendons and provide information regarding orientation of one body segment with respect to another. Compared with vestibular and visual inputs, these sensors have lower thresholds for motion detection and operate at significantly higher frequencies. Proprioceptive input provides critical information regarding the point of contact with the ground, which can be extrapolated to detect orientation and movement of the body. Proprioceptive cues from the neck also play an important role in detecting head orientation and in providing a stable platform for vestibular and visual receptors.

The proprioceptive system undergoes several age-related changes. Vibration and touch thresholds decline in older individuals, adversely affecting tactile information arising from the feet at their contact point with the ground. Similarly, the ability to detect the position and direction of joint movements declines with age.

A number of studies have demonstrated decreased postural stability when proprioceptive input is altered in such a way that it provides inaccurate information regarding orientation. Horak et al. compared the performance of patients with severe neuropathy with age-matched controls and demonstrated that the performance of the control subjects became similar to that of patients with neuropathy for test conditions in which proprioceptive input was altered. Therefore, it is not surprising that reduction of vibration and tactile sensation at the ankle and knee joints has been associated with an increased risk of falls in the elderly.

Concomitant conditions such as diabetes mellitus or other causes of peripheral neuropathy that can be more common in older patients may have a synergistic effect with age-related decline in lower extremity proprioceptive function. Peripheral neuropathy itself is predictive of falls in patients with bilateral vestibulopathy.

The role of neck proprioception on postural control has been studied using neck muscle vibration. Prolonged unilateral vibration of neck muscles during in-place stepping caused subjects to rotate about a vertical axis away from the side of vibration. Using a similar type of neck vibration during locomotion, Deshpande and Patla demonstrated reduced sensitivity of neck proprioception in older adults. This is an important observation because as noted before, age-related decline of the vestibular system usually involves bilateral reduction of function. In younger patients with bilateral vestibular loss, neck receptors play an important role as substitutes for the vestibular system. This mode of compensation may not be available in the elderly because of reduced neck proprioception.

Visual system

The visual system undergoes significant age-related changes. In addition to visual acuity, several other visual functions, such as depth perception, accommodation, contrast sensitivity, and dark adaptation, decline with age. Deficits in depth perception and contrast sensitivity have been shown to have the largest contributory influence on falls. These impairments affect the ability of older adults to accurately judge distances and to avoid obstacles.

Age-related changes in static visual acuity as measured with stationary subjects and stationary targets have been studied extensively. The association between reduced static visual acuity and balance problems in the elderly is still in dispute. Deterioration of dynamic visual acuity, in which either the target or the subject is moving, has also been documented in older individuals. Interestingly, patients with acute unilateral and bilateral vestibular lesions also exhibit impaired dynamic visual acuity and complain of blurred vision during head movements. The coexistence of this impairment in the elderly and in patients with known balance disorders may explain some of the symptoms in older adults.

It has been shown that reliance on visual input increases with age. For example, older subjects exposed to moving visual surrounds were affected more and demonstrated greater postural sway than younger subjects. Although both older and younger subjects were able to adapt to moving visual stimuli, older individuals required significantly more time for adaptation to occur. In addition, postural sway of older subjects who were presented with spatially inaccurate visual stimuli was significantly greater than the response of younger subjects.

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