Pain Severity Is Associated with Self-Reported Functional Limitations: Findings from the 2018 Medical Expenditure Panel Survey (MEPS)

This is the authors' abstract. We don't add key points for this paper.

Dear Editor, Pain is a prevalent, complex condition that can result in disability, poorer quality of life, poor mental health, interference with daily activities and relationships, lower work productivity, and greater health care resource utilization and costs [1]. The present study aimed to address a knowledge gap by assessing the association between self-reported pain severity and self-reported functional limitations among adults in the United States. This retrospective, cross-sectional study included participants ≥18 years of age in the 2018 Medical Expenditure Panel Survey (MEPS) full-year consolidated data file [2]. MEPS participants voluntarily responded to items asked during multiple interviews. The study outcome was presence of a self-reported functional limitation (yes, no), defined as “difficulty walking, climbing stairs, grasping objects, reaching overhead, lifting, bending or stooping, or standing for long periods of time” [2]. The independent variable was self-reported pain severity, defined by the item, “During the past four weeks, how much did pain interfere with your normal work, including both work outside the home and housework?” (not at all, a little bit, moderately, quite a bit, extremely) [2]. Characteristics of study participants were compared among pain severity levels through the use of chi-squared tests. Multivariable logistic regression was used to assess the association between self-reported pain severity and self-reported functional limitations, with adjustment for the following variables: sex, age, race/ethnicity, marital status, education, employment, income, comorbid conditions, body mass index, frequent exercise, and smoking status [2]. All logistic regression assumptions were assessed and met. Analyses were conducted with survey procedures in SAS 9.4 (SAS Institute Inc., Cary, NC, USA). Analyses accounted for clusters and strata in the complex MEPS design and were weighted to produce nationally representative estimates. The a priori significance level was α < 0.05. The University of Arizona Institutional Review Board approved this study (#2006721124; June 12, 2020). This study included 18,942 individuals, representing a weighted population of 241,984,432 (no pain = 152,906,808, little pain = 52,567,607, moderate pain = 17,547,129, quite a bit of pain = 13,606,888, extreme pain = 5,356,001). Table 1 describes characteristics of the study participants. Table 2 displays multivariable logistic regression results for associations between self-reported pain severity and self-reported functional limitations. Characteristics of study participants (U.S. adults ≥18 years of age) stratified by pain severity in the 2018 MEPS (N = 18,942) 95% CI = 95% confidence interval. Differences between pain severity groups were compared through the use of chi-squared tests. There were statistically significant differences between pain severity groups for all variables (P < 0.0001). Characteristics of study participants (U.S. adults ≥18 years of age) stratified by pain severity in the 2018 MEPS (N = 18,942) 95% CI = 95% confidence interval. Differences between pain severity groups were compared through the use of chi-squared tests. There were statistically significant differences between pain severity groups for all variables (P < 0.0001). Adjusted association between pain severity and functional limitations among U.S. adults (≥18 years of age) in the 2018 MEPS Bold font indicates statistical significance at P < 0.05. c-statistic = 0.898. Adjusted association between pain severity and functional limitations among U.S. adults (≥18 years of age) in the 2018 MEPS Bold font indicates statistical significance at P < 0.05. c-statistic = 0.898. This study found that greater levels of self-reported pain severity were associated with greater odds of reporting a functional limitation compared with no pain in adjusted analyses. This concurs with existing knowledge that those who report pain generally suffer from poorer health and more limitations in daily life than do individuals without pain [3]. The observations that females (vs males), those ≥40 (vs <40) years of age, and non-Hispanic whites (vs Hispanics) had greater odds of reporting a functional limitation in the present study are perhaps not surprising, given that women typically experience more functional limitations than men do [4] and that functional limitations are common among older adults, which can be attributed to natural life progression. The effect of ethnicity could be due to cultural variation in how individuals from different backgrounds perceive and report pain, which has an impact on functional limitations [5]. The finding that unmarried (vs married) U.S. adults had greater odds of reporting a functional limitation could be attributed to spouses (particularly women) acting as caregivers for partners, helping with activities, and thereby mitigating the likelihood of their partners’ reporting functional limitations. In previous work, it has been found that specific problems in mobility, hand function, fatigue, and cognitive performance were associated with increased odds of becoming unemployed [6], which might explain why, in the present study, adults who were unemployed also had greater odds of reporting a functional limitation than did those who were employed. A reason to explain why U.S. adults in this study who were poor or had low income (vs middle/high income) had greater odds of reporting a functional limitation could be that low-income individuals forgo care because of cost and often must self-manage their health conditions [7]. Finally, the present study found that U.S. adults who reported having ≥5 (vs <5) comorbid conditions, were obese (vs not obese), and did not frequently exercise (vs did frequently exercise) had greater odds of reporting a functional limitation. Previous work has shown that individuals with comorbid conditions might become functionally impaired earlier than those with fewer comorbid conditions do [8] and that obese older adults reported more impaired physical functioning, lower quality of life, greater physical mobility limitation, more gross and fine motor limitations, and more difficulties with activities of daily living than normal-weight individuals did [9]. Previous work has also shown that physical functioning, reduction of pain, and disability improved in those who exercised [10] and suggests that frequent exercise has a protective effect against developing a functional limitation. As comorbid conditions, obesity, and exercise can be practically addressed through appropriate lifestyle interventions and treatment options, these findings could help inform decision-making on health care interventions to better manage care and help improve health outcomes for people with functional limitations. Study limitations include the subjective nature and varied definitions of pain and functional limitations (pain data were collected on the basis of how much pain interfered with the ability to do normal tasks rather than a visual analog scale or numeric pain rating scale, whereas functional limitations were collected as a dichotomous variable); use of secondary, self-reported data; and the inability to determine directionality between self-reported pain severity and the other variables with self-reported functional limitations because of the retrospective, cross-sectional nature of the study. In conclusion, this study showed that, relative to those without pain, greater levels of pain severity were associated with greater odds of reporting a functional limitation, which indicates the need to better manage pain and reduce functional limitations among U.S. adults ≥18 years of age. This study also showed that several other characteristics were associated with reporting a functional limitation, but some of these variables are more easily modifiable through public health interventions (e.g., body mass index, exercise status) than others are (e.g., age, sex). Findings from this study provide contemporary, detailed insight and add to the existing evidence for associations between pain severity and other factors with functional limitations among U.S. adults. These findings should be considered by policy makers, health care professionals, and other stakeholders in the development of strategies and interventions to optimize health care, improve pain management, and reduce functional limitations among U.S. adults. Funding sources: This study received no funding. Conflicts of interest: Dr. Axon reports grant funding from the American Association of Colleges of Pharmacy, Arizona Department of Health, Merck & Co., National Council for Prescription Drug Programs, Pharmacy Quality Alliance, and Tabula Rasa HealthCare Group, outside of this study.

Pain severity linked to functional limitations; leaves open causality and directionality in US adults.