Pain in Older Persons

Introduction

Pain is highly prevalent in older people. Up to 40% of elders living independently ( ) and 80% of those in institutional settings ( ) report pain. Similar to younger individuals, pain in older people is associated with significant psychological distress and impaired physical function ( ). Nonetheless, older patients are at risk for inadequate treatment ( ). Multiple interacting factors probably contribute to this, but inadequate assessment may be a primary barrier ( ). Although information regarding pain and aging is now more readily available, many gaps in our knowledge remain. In this chapter we describe the validity and reliability of popular pain scales for use in the assessment of older people. We then critically review the data regarding age differences in the experience of experimental, acute, and chronic cancer and non-cancer pain.

Assessment of Pain Across the Adult Life Span

Appropriate assessment is essential to both pain research and management. Pain that is not recognized cannot be treated, whereas treatment initiated without adequate assessment is potentially dangerous. A comprehensive pain assessment must consider the multiple interacting biopsychosocial factors that contribute to the experience of pain ( ). The age of the person being assessed is an important consideration because it may influence the selection and administration of tools, as well as the goals and outcomes of treatment. Age-related visual, auditory, or cognitive impairments can hinder completion of assessment protocols and must be accommodated ( ). In addition, older people may be less able than younger people to tolerate the burden of long assessment sessions, necessitating modification in protocols, such as completion of longer questionnaires over multiple sessions ( ).

Another age-related factor that must be considered is the presence and impact of co-morbid conditions, including core geriatric syndromes such as frailty, pressure ulcers, incontinence, falls, functional decline, and delirium ( ). Co-morbidities are associated with polypharmacy ( ), which may have a further impact on pain and function. Therefore, a comprehensive pain assessment should be sensitive to the distinct needs of older people and must include standardized and validated measures of co-morbidity, medication use, and cognitive, physical, and psychological function.

Measures of Pain Intensity

The most frequently assessed component of pain is intensity: how much it hurts. Most pain scales were designed for use in younger adults, but their use in older people has been a growing research focus. The data available support the use of the following pain intensity measures in older people: verbal descriptor scales (VDSs), numerical rating scales (NRSs), box scores, facial pain scales (FPSs), and pain thermometers. These scales have been associated with high completion rates, moderate to good concurrent and construct validity, and acceptable test–retest reliability ( , , ). There is evidence of comparable sensitivity across age groups for NRSs and FPSs ( , ). However, data regarding the sensitivity of VDSs are mixed ( , ). In addition, the construct validity of FPSs, that is, the extent to which they are interpreted as uniquely portraying pain rather than other physical symptoms or emotional states, may be inadequate in older people ( ).

Caution is necessary when using visual analog scales (VASs) in older patients. Increasing age has been associated with a higher frequency of incomplete or unscorable responses ( Fig. 22-1 ) ( , , ). These difficulties may be related to psychomotor and cognitive impairment ( , ). Among older people who can complete them, VASs show poor convergent validity, or lack of agreement with other intensity measures ( , ). In addition, they may not be sufficiently sensitive to detect age differences, although they may be as sensitive as other intensity measures to detect changes over time in older patients ( ). Finally, older patients report that VASs are more difficult to complete and are a poorer description of pain than other scales ( ). More research is needed to elucidate the cognitive demands of VASs and the ways in which performance may be affected by age.

Age Differences in Experimental Pain

Studies of age differences in pain threshold have been inconsistent, with reports that threshold increases, decreases, or does not change with increasing age ( ). Similarly, both increased and decreased pain tolerance with age has been reported ( ). These disparate findings may be the result, in part, of methodological weaknesses and diversity of the studies. For example, there is considerable variability in the mean age of the groups being compared, the pain induction methods used, and the psychophysical end points measured. Subject inclusion and exclusion criteria and sufficient statistical data to allow comparison across studies are often not provided. In addition, several studies do not include adequate numbers of older subjects. Despite these methodological limitations, the majority of studies indicate that there is an increase in the thermal and pressure pain threshold and a decrease in pain tolerance with age, but no change in sensitivity to electrical stimulation. There is also evidence of increased sensitivity to ischemic pain with age. The cross-modality differences in age-related patterns are not surprising given that each type of stimulation may engage slightly different neural processes, which may not be uniformly affected by aging.

Neurobiology of Pain and Aging

It is likely that the age differences just described are the end result of multiple, interacting neurobiological and behavioral factors. In the periphery, age-related changes in characteristics of the skin ( ) and nociceptors ( ) may be important. In addition, both C-fiber ( ) and Aδ-fiber ( ) functions decrease with age. Coupled with age-related changes in the neuroimmunological response to tissue injury ( ), this may contribute to the decreased neuroplasticity evident throughout the central nervous system ( ). Consistent with this finding, when compared with younger people, older people show prolonged hyperalgesia ( ), altered temporal summation ( , ), and impaired descending endogenous inhibition ( , ) in response to experimental pain paradigms. Taken together, these findings suggest that adaptation to painful stimuli and injury may be impaired with advancing age, thereby possibly increasing vulnerability to persistent pain.

Recent imaging studies have shown that older people have smaller responses than younger people to thermal stimulation in several brain regions, including the primary somatosensory cortex, anterior insula, and supplementary motor area ( ). However, a different pattern of age-related activation was found in response to pressure stimulation ( ). Importantly, there is preliminary evidence that older people with chronic pain may have structural brain changes when compared to older people without pain ( ). More research will be needed to further elucidate age- and pain-related patterns of brain activation in response to nociceptive stimulation and ongoing clinical pain.

The neurobiology of aging and its implications for pain sensitivity remain to be elucidated. Undoubtedly, there is an interaction of both peripheral and central changes, including changes in emotional and cognitive factors. Perhaps the patterns of age differences in pain reflect the differential effects of age on the integrity or activity levels of these systems. There is evidence that age-related changes in the neurobiological substrates of pain are not uniform throughout the central nervous system ( ). Importantly, the implications of these changes for clinical painful states remain to be determined. Experimental pain paradigms provide an oversimplified approximation of both the acute and chronic pain experience, in part because the important role that psychological and emotional factors play in pathological pain states cannot be modeled in the experimental setting ( ). The relevance of the mechanisms underlying differences in experimental pain reactivity must be evaluated in the clinical setting. It would not be surprising to find that the mechanisms vary across different types of pain.