Journal of Gerontology: MEDICAL SCIENCES Cite journal as: J Gerontol A Biol Sci Med Sci. 2010 August;65(8):880–886 doi:10.1093/gerona/glq039
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[email protected]. Advance Access published on March 29, 2010
The Association Between Noncancer Pain, Cognitive Impairment, and Functional Disability: An Analysis of the Canadian Study of Health and Aging Joseph W. Shega,1 Debra K. Weiner2,3 Judith A. Paice,4 S. Pinar Bilir,1 Kenneth Rockwood,5 Keela Herr,6 Mary Ersek,7 Linda Emanuel,8 and William Dale1,9 1Section
of Geriatrics and Palliative Medicine, Department of Medicine, University of Chicago, Illinois. of Medicine, Department of Psychiatry and Department of Anesthesiology, University of Pittsburgh, Pennsylvania. 3Department of Medicine, Geriatric Research, Education and Clinical Center, VA Pittsburgh Healthcare, Pennsylvania. 4Department of Medicine, Division of Hematology Oncology, Feinberg School of Medicine and Northwestern University, Chicago, Illinois. 5Department of Medicine, Division of Geriatric Medicine, Dalhousie University, Halifax, Nova Scotia, Canada. 6College of Nursing, University of Iowa. 7School of Nursing, University of Pennsylvania, Philadelphia. 8Buehler Center on Aging, Northwestern University, Chicago, Illinois. 9Section of Hematology and Oncology, Department of Medicine, University of Chicago, Illinois. 2Department
Address correspondence to Joseph W. Shega, MD, Section of Geriatrics and Palliative Medicine (MC 6098), Department of Medicine, 5841 South Maryland Avenue, Chicago, IL 60637. Email:
[email protected]
Background. Noncancer pain and cognitive impairment affect many older adults and each is associated with functional disability, but their combined impact has yet to be rigorously studied. Methods. This is a cross-sectional analysis of the Canadian Study of Health and Aging. Pain was collapsed from a 5-point to a dichotomous scale (no and very mild vs moderate and greater). Cognitive status was dichotomized from the Modified Mini-Mental State Examination (0–100) to no (>77) or mild-moderate (77–50) impairment. Five Instrumental Activities of Daily Living (IADL) and seven Activities of Daily Living (ADL) were self-rated as “accomplished without any help” (0), “with some help” (1), or “completely unable to do oneself” (2) and then summed to create a composite score of 0–10 and 0–14, respectively. Multivariate linear regression analysis was conducted to determine the associations between self-reported functional status with moderate or greater pain, cognitive impairment, and the interaction of the two. Results. A total of 5,143 (90.2%) participants were eligible, 1,813 (35.6%) reported pain at a moderate intensity or greater and 727 (14.3%) were cognitively impaired. The median IADL and ADL summary scores increased among the pain and cognition categories in the following order: no pain and cognitively intact (0.63 SD 1.24, 0.23 SD 0.80), pain and cognitively intact (1.18 SD 1.69, 0.57 SD 1.27), no pain and cognitively impaired (1.64 SD 2.22, 0.75 SD 1.57), and pain and cognitively impaired (2.27 SD 2.47, 1.35 SD 2.09), respectively. Multivariate linear regression found IADL summary scores were associated with pain, coefficient .17 (95% confidence interval [CI] 0.07–0.26), p < .01; cognitive impairment, coefficient .67 (95% CI 0.51–0.83), p < .01; and an interaction effect of pain with cognitive impairment, coefficient .24 (95% CI 0.01–0.49), p = .05. ADL summary scores were associated with pain coefficient .10 (95% CI 0.04–0.17), p < .01 and cognitive impairment, coefficient .29 (95% CI 0.19–0.39), p < .01, but had a nonsignificant interaction term, coefficient .12 (95% CI −0.03 to 0.29), p = .12. Conclusions. Noncancer pain and cognitive impairment are independently associated with IADL and ADL impairment and IADL impairment is even greater when both conditions are present. Key Words: Noncancer pain—Cognitive impairment—Function—Dementia—Older adult. Received November 17, 2009; Accepted February 25, 2010 Decision Editor: Luigi Ferrucci, MD, PhD
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ANY conditions associated with noncancer pain, such as osteoarthritis, spinal stenosis, and osteoporosis, are more prevalent with age and often affect multiple physical sites (1–3). Given this, it is not surprising that noncancer pain is reported by more than 40% of communitydwelling adults aged 75 or older (4–6). Of those reporting pain, a sizable proportion experience pain of at least moder880
ate intensity. The impact of pain goes beyond physical discomfort and suffering as its presence is also associated with depression, decreased social interaction, and functional impairment (7,8). The prevalence of cognitive impairment also increases with age so that by age 85 as many as 50% of older adults may be affected (9,10). The diagnosis of cognitive impairment is
PAIN DEMENTIA FUNCTION
important as its course is typically characterized by gradual, yet progressive, memory loss and functional decline (11). The functional decline generally progresses in a stepwise fashion with the loss of more complex Instrumental Activities of Daily Living (IADL) such as driving, shopping, or cooking occurring earlier than basic Activities of Daily Living (ADL) such as bathing, walking, or dressing (12). We conducted the current analyses to try to understand the relationships among noncancer pain, cognitive impairment, and functional disability. Our goal was to better characterize the contribution of self-reported pain and cognitive function to self-reported independence in IADL and ADL. We also wanted to determine whether noncancer pain and cognitive impairment interact, resulting together in more impaired physical function than can be explained by their independent contributions. A more indepth understanding of these relationships is particularly relevant as functional status decrements are associated with poor outcomes including falls, institutionalization, and death (13,14). The clinical implication of such an interaction would be that effective pain management in those with cognitive impairment may help mitigate excessive functional decline.
Methods
Participants This study is a cross-sectional analysis of the Canadian Study of Health and Aging (CSHA). The CSHA was a national longitudinal study designed to provide information about the epidemiology of dementia. People aged 65 and older were recruited with representative samples drawn from 36 cities and their surrounding rural areas across Canada. Details of the study’s objectives, design, and methodologies have been described elsewhere (15,16). The interviews were conducted in participant homes by trained research personnel and included demographic characteristics along with health, disease, mood, physical function, and cognition measures. This analysis includes participants who resided in the community and completed the questionnaire at the time of the second wave in 1996. Data from this wave incorporated a pain assessment measure that was not included in the other waves. Otherwise eligible participants were excluded from the analyses if the pain, cognition, or functional measure were missing, participants had greater than moderate cognitive impairment (as this affects the reliability of the pain and function questions) (8), or they reported having cancer in the past year (to focus only on noncancer pain). All participants provided written informed consent and the CSHA protocol was approved at each participating institution in Canada. The research plan for the secondary analyses was reviewed and approved by the University of Chicago’s Institutional Review Board.
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Measures Pain and cognition were the independent variables in the current study. Noncancer pain was assessed using the 5-point Verbal Descriptor scale, which measures the presence and intensity of pain. The validity and reliability of this measure has been established in both cognitively intact and impaired populations (17–20). Participants were asked, “How much bodily pain have you had during the past 4 weeks?” The response categories offered were: 1 = none, 2 = very mild, 3 = moderate, 4 = severe, and 5=very severe. The responses were dichotomized as “none or very mild” and “moderate or greater” as the latter level is considered clinically relevant as it adversely affects health (21). Cognitive status was assessed using the Modified MiniMental State Examination (3MS). The 3MS is similar to the Folstein Mini-Mental Exam, but adds four tasks (date and place of birth, animal naming, similarities, and a second delayed recall) and allows partial credit on some items (22). The 3MS has a range from 0 to 100 with lower scores indicating greater cognitive impairment. The 3MS has been validated in a variety of community-dwelling populations including the CSHA and a score of 77 or less indicates cognitive impairment with sufficient sensitivity and specificity to be used for screening purposes (23,24). Functional status was ascertained using the Older Americans Resources and Services’ IADL and ADL (25). This selfreport measure has previously been validated in cognitively intact persons as well as those with mild to moderate cognitive impairment (26). Each of five IADL (getting to distant places, using the telephone, going shopping, preparing own meals, and doing housework) and seven ADL (eating, dressing, personal care, walking, getting out of bed, taking a bath, and using the toilet) were included as part of the interview. Participants categorized their independence by indicating whether or not they could perform each activity without any help (0), with some help (1), or completely unable to do oneself (2). IADL and ADL self-reports were summed to develop a composite score for each, ranging from 0 to 10 for IADL and 0–14 for ADL, where higher scores indicate greater impairment. Functional impairment when used as a dichotomous variable was defined as any help needed to perform any of the five IADLs or any of the seven ADLs. In other words, impairment was defined as any summary score of 1 or greater for either measure. The analyses also incorporated participant demographics, a depression screen (5-item mental health screening questionnaire) (27), self-reported medical comorbidities, and self-reported health status. Demographic variables included age, gender, race and ethnicity, education, and marital status. Mood was assessed using a 5-item self-report mental health screening questionnaire (27). Each of the five questions assess mental health (feelings of anxiety and depression) on a 6-point scale ranging from “none of the time” to “all of the time,” where higher scores indicate more symptoms of depression and total scores range from 5 to 30.
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Comorbidities were assessed by asking participants about conditions present in the past year from 15 body systems, and each was dichotomized as “yes” or “no.” The list included high blood pressure, heart or circulation problems, arthritis or rheumatism, Parkinson’s disease or other neurological problem, eye trouble, ear trouble, chest problems, trouble with stomach or digestive system, back problems, bladder control problems, problems controlling bowels, fractures, cancer, diabetes, and foot problems. Affirmative responses were summed to create an overall comorbidity index ranging from 0 to 15, with higher scores indicating greater morbidity. Self-reported health status was assessed using a 5-point scale ranging from poor to excellent health. Statistical Analyses A power analysis was conducted to determine the feasibility of using the CSHA data set to examine our hypothesis that noncancer pain and cognitive impairment interact to affect function in a nonlinear manner. In the CSHA, the prevalence of cognitive impairment was estimated to be 16%, so that among 5,000 participants, 800 persons would be cognitively impaired. Also, approximately 40% of participants, independent of cognitive status, had pain at a moderate intensity or higher, leaving 1,680 cognitively intact and 320 cognitively impaired participants with pain and 2,520 and 480 participants without pain, respectively. These sample sizes have an 80% power to detect an interaction effect between noncancer pain and cognition of 10%, assuming a Type I error rate of 5% and a two-tailed test. Individual characteristics were analyzed by pain status (no or very mild pain versus moderate or greater pain) using chi-squared analysis for categorical variables. Mann–Whitney U tests (also referred to as Wilcoxon rank sum test) were used to analyze these differences for continuous variables due to their nonnormal distributions. Participants were subsequently divided into four groups based upon whether or not pain was reported at a moderate intensity or greater, and whether cognitive impairment was present. The four resultant groups were no pain and cognitively intact, pain and cognitively intact, no pain and cognitively impaired, and pain and cognitively impaired. Chi-square analysis was used to analyze differences among these aggregates. Multivariate linear regression analysis was conducted to determine the associations between self-reported functional status with moderate or greater pain, cognitive impairment, and the interaction of the two. Analyses were performed separately for IADL and ADL summary scores as the dependent variable. Additional independent variables included factors significantly associated with the dependent variables in univariate analysis (p < .10), as well as factors that adjust for baseline differences in groups of interest. A correlation matrix was computed for all potential independent variables to assess collinearity and for variables that were highly correlated; inclusion in the final models was based on clinical
Table 1. Participant Characteristics by Severity of Noncancer Pain Self-Report, N = 5,086 Characteristic Age, mean (SD) Female gender (%) White race (%) Education (%) 8 years or less 9–12 years 13 or more years Marital status (%) Single Married Widowed/divorced/ separated Lives alone (%) Comorbidity, mean (SD)* Health status, % very good or good Depression score, mean (SD)† Cognitively impaired‡ (%)
Moderate or Greater None or Mild Pain Pain (N = 1813, 35.6%) (N = 3273, 64.4%) p Value 79.9 (6.0) 67.4 96.9
79.4 (6.1) 55.5 96.7
31.9 43.9 23.2
28.9 43.8 27.3
.02
6.5 45.7 47.8
6.7 49.6 43.7
.02
43.0 4.7 (2.3)
39.4 3.1 (2.0)
.01
