title: Unpacking the burden: understanding the relationships between chronic pain and comorbidity in the general population.
abstract: We investigated the association of chronic pain with physical and mental comorbidity in the New Zealand population by measuring chronic pain status separate from comorbid conditions. Models of allostatic load provided a conceptual basis for considering multi-morbidity as accumulated comorbid load and for using both discrete conditions and cumulative measures in analyses. The nationally representative cross-sectional survey data included self-reported doctor-diagnosed chronic physical and mental health conditions, Kessler 10-item scale scores, an independent measure of chronic pain, and sociodemographic characteristics. The population prevalence of chronic pain is 16.9%, and a quarter (26%) of the population report 2 or more comorbid physical conditions statistically associated with chronic pain (unadjusted P<0.01). Results indicate that accumulated comorbid load is independently associated with chronic pain. Six physical conditions independently associated with chronic pain (adjusted odds range from 1.4 to 3.9) increase the risk of chronic pain in an additive manner, and residual accumulated load further increases risk for 2 or more conditions (adjusted odds 1.6). Anxiety/depression interacts synergistically with arthritis and neck/back disorders to increase the odds of reporting chronic pain beyond an additive model. This synergistic effect is not apparent for other conditions or for additional comorbid load. Results imply that measurement of chronic pain independent of comorbid conditions and adjustment for comorbid conditions is important for more accurate prevalence estimates and understanding relationships between conditions. Future epidemiological research might usefully incorporate independent measurement of chronic pain alongside adjustment for specific physical and mental health conditions as well as accumulated comorbid load.
authors.affiliation: Pain Management Research Institute - University of Sydney at Royal North Shore Hospital, Sydney, Australia School of Public Health, University of Sydney, Sydney, Australia.
authors.forename: Clare H
authors.initials: CH
authors.lastname: Dominick
authors.forename: Fiona M
authors.initials: FM
authors.lastname: Blyth
authors.forename: Michael K
authors.initials: MK
authors.lastname: Nicholas
mesh_terms: D059350:Chronic Pain / Q000453:epidemiology* / Q000208:ethnology / Q000523:psychology; D015897:Comorbidity / Q000639:trends; D017281:Cost of Illness; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D019964:Mood Disorders / Q000453:epidemiology* / Q000208:ethnology; D009140:Musculoskeletal Diseases / Q000453:epidemiology* / Q000208:ethnology / Q000523:psychology; D009520:New Zealand / Q000453:epidemiology; D010147:Pain Measurement / Q000379:methods; D015995:Prevalence
references.citation: Ahlbom A, Alfredsson L. Interaction: a word with two meanings creates confusion. Eur J Epidemiol. 2005;20:563-564.
references.citation: Andersson T, Alfredsson L, Kallberg H, Zdravkovic S, Ahlhom A. Calculating measures of biological interaction. Eur J Epidemiol. 2005;20:575-579.
references.citation: Arnow BA, Hunkeler EM, Blasey CM, Lee J, Constantino MJ, Fireman B, Kraemer HC, Dea R, Robinson R, Hayward C. Comorbid depression, chronic pain and disability in primary care. Psychosom Med. 2006;68:262-268.
references.citation: Asmundson GJ, Katz J. Understanding the co-occurrence of anxiety disorders and chronic pain: state-of-the-art. Depress Anxiety. 2009;26:888-901.
references.citation: Bair MJ, Wu J, Damush TM, Sutherland JM, Kroenke K. Association of depression and anxiety alone and in combination with chronic musculoskeletal pain in primary care patients. Psychosom Med. 2008;70:890-897.
references.citation: Baune B, Caniato R, Garcia-Alcaraz MA, Berger K. Combined effects of major depression, pain and somatic disorders on general functioning in the general adult population. Pain. 2008;138:310-317.
references.citation: Blyth FM, Rochat S, Cumming RG, Creasey H, Handelsman DJ, Le Couteur DG, Naganathan V, Sambrook PN, Seibel MJ, Waite LM. Pain, frailty and comorbidity on older men: the CHAMP study. Pain. 2008;140:224-230.
references.citation: Boyd CM, Fortin M. Future of multimorbidity research: how should understanding of multimorbidity inform health system design? Public Health Rev. 2010;32:1-18.
references.citation: Buse DC, Manack A, Serrano D, Turkel C, Lipton RB. Sociodemographic and comorbidity profiles of chronic migraine and episodic migraine sufferers. J Neurol Neurosurg Psychiatry. 2010;81:428-432.
references.citation: Butchart A, Kerr EA, Heisler M, Piette JD, Krien SL. Experience and management of chronic pain among patients with other complex chronic conditions. Clin J Pain. 2009;25:293-298.
references.citation: Campbell-Scherer D. Multi-morbidity: a challenge for evidence-based medicine. Evid Based Med. 2010;15:165-166.
references.citation: Demyttenaere K, Bruffaerts R, Lee S, Levinson D, de Girolamo G, Nakane H, Mneimneh Z, Lara C, de Graaf R, Scott KM, Gureje O, Stein DJ, Haro JM, Bromet EJ, Kessler RC, Alonso J, von Korff M. Mental disorders among persons with chronic back or neck pain: results from the world mental health surveys. Pain. 2007;129:332-342.
references.citation: Dominick CH, Blyth FM, Nicholas MK. Patterns of chronic pain in the New Zealand population. N Z Med J. 2011;124:63-76.
references.citation: Eriksen J, Jensen MK, Sjogren P, Ekholm O, Rasmussen NK. Epidemiology of chronic non-malignant pain in Denmark. Pain. 2003;106:221-228.
references.citation: Furukawa TA, Kessler RC, Slade T, Andrews G. The performance of the K6 and K10 screening scales for psychological distress in the Australian National Survey of Mental Health and Well-Being. Psychol Med. 2003;33:357-362.
references.citation: Ganzel BL, Morris PA, Wethington E. Allostasis and the human brain: integrating models of stress from the social and life sciences. Psychol Rev. 2010;117:134-174.
references.citation: Gatchel RJ. Comorbidity of chronic pain and mental health disorders: the biopsychosocial perspective. Am Psychol. 2004;59:795-805.
references.citation: Gureje O, Akinpelu AO, Uwakwe R, Udofia O, Wakil A. Co-morbidity and impact of chronic spinal pain in Nigeria. Spine. 2007;32:E495-E500.
references.citation: International Association for the Study of Pain. Classification of chronic pain. Description of pain syndromes and definition of pain terms. Pain. 1986;3:S1-226.
references.citation: Juster R, McEwen BS, Lupien SJ. Allostatic load biomarkers of chronic stress and impact on health and cognition. Neurosci Biobehav Rev. 2010;35:2-16.
references.citation: Kamaleri Y, Natvig B, Ihlebaek CM, Bruusgaard D. Does the number of musculoskeletal pain sites predict work disability? A 14-year prospective study. Eur J Pain. 2009;13:426-430.
references.citation: Kessler RC, Andrews G, Colpe LJ, Hiripi E, Mroczek DK, Normand ST, Walters EE, Zaslavsky AM. Short screening scales to monitor population prevalences and trends in non-specific psychological distress. Psychol Med. 2002;32:959-976.
references.citation: Kessler RC, Barker PR, Colpe LJ, Epstein JF, Gfroerer JC, Hiripi E, Howes MJ, Normand ST, Manderscheid RW, Walters EE, Zaslavsky AM. Screening for serious mental illness in the general population. Arch Gen Psychiatry. 2003;60:184-189.
references.citation: Leeuw M, Goossens MEJB, Linton SJ, Crombez G, Boersma K, Vlaeyen JWS. The fear-avoidance model of musculoskeletal pain: current state of scientific evidence. J Behav Med. 2007;30:77-94.
references.citation: Linton SJ, Bergbom S. Understanding the link between depression and pain. Scand J Pain. 2011;2:47-54.
references.citation: Mattei J, Demissie S, Falcon LM, Ordovas JM, Tucker K. Allostatic load is associated with chronic conditions in the Boston Puerto Rican Health Study. Soc Sci Med. 2010;70:1988-1996.
references.citation: McEwen BS, Gianaros PJ. Central role of the brain in stress and adaptation: links to socioeconomic status, health and disease. Ann N Y Acad Sci. 2010;1186:190-222.
references.citation: Mercer SW, Smith SM, Wyke S, O’Dowd T, Watt GCM. Multimorbidity in primary care: developing the research agenda. Fam Pract. 2009;26:79-80.
references.citation: Munce SEP, Stewart DE. Gender differences in depression and chronic pain conditions in a national epidemiologic survey. Psychosomatics. 2007;48:394-399.
references.citation: Oakley Browne MA, Wells JE, Scott KM, McGee MA. The Kessler Psychological Distress Scale in Te Rau Hinengaro: the New Zealand mental health survey. Aust N Z J Psychiatry. 2010;44:314-322.
references.citation: Ohayon MM, Schatzberg AF. Chronic pain and major depressive disorder in the general population. J Psychiatr Res. 2010;44:454-461.
references.citation: Pearce N. Analytical implications of epidemiological concepts of interaction. Int J Epidemiol. 1989;18:976-980.
references.citation: Rao JNK, Wu CFJ. Resampling inference with complex survey data. J Am Stat Assoc. 1988;83:231-241.
references.citation: Rashiq S, Dick BD. Factors associated with chronic noncancer pain in the Canadian population. Pain Res Manag. 2009;14:454-460.
references.citation: Roy-Byrne PP, Davidson KW, Kessler RC, Asmundson GJ, Goodwin RD, Kubzansky L, Lydiard RB, Massie MJ, Katon W, Laden SK, Stein MB. Anxiety disorders and comorbid medical illness. Gen Hosp Psychiatry. 2008;30:208-255.
references.citation: Sareen J, Cox BJ, Clara I, Asmundson GJ. The relationship between anxiety disorders and physical disorders in the US National Comorbidity Survey. Depress Anxiety. 2005;21:193-202.
references.citation: Sareen J, Jacobi F, Cox BJ, Belik S-L, Clara I, Stein MB. Disability and poor quality of life association with comorbid anxiety disorders and physical conditions. Arch Intern Med. 2006;166:2109-2116.
references.citation: Scott K, McGee MA, Schaaf D, Baxter J. Mental–physical comorbidity in an ethnically diverse population. Soc Sci Med. 2008;66:1165-1173.
references.citation: Seeman T, Epel E, Gruenewald T, Karlamangla A, McEwen BS. Socio-economic differentials in peripheral biology: cumulative allostatic load. Ann N Y Acad Sci. 2010;1186:223-239.
references.citation: Siddall PJ, Cousins MJ. Persistent pain as a disease entity: implications for clinical management. Anesth Analg. 2004;99:510-520.
references.citation: Stanton AL, Revenson TA, Tennen H. Health psychology: psychological adjustment to chronic disease. Annu Rev Psychol. 2007;58:565-592.
references.citation: Tracey I, Bushnell MC. How neuroimaging studies have challenged us to rethink: is chronic pain a disease? J Pain. 2009;10:1113-1120.
references.citation: Tsang A, Von Korff M, Lee S, Alonso J, Karam E, Angermeyer MC, Borges GL, Bromet EJ, de Girolamo G, de Graaf R, Gureje O, Lepine JP, Haro JM, Levinson D, Oakley Browne MA, Posada-Villa J, Seedat S, Watanabe M. Common chronic pain conditions in developed and developing countries: gender and age differences and comorbidity with depression–anxiety disorders. J Pain. 2008;9:883-891.
references.citation: Verhaak PFM, Kerssens JJ, Dekker J, Sorbi MJ, Bensing JM. Prevalence of chronic benign pain disorder among adults: a review of the literature. Pain. 1998;77:231-239.
references.citation: Von Korff M, Crane P, Lane M, Miglioretti DL, Simon G, Saunders K, Stang P, Brandenburg N, Kessler RC. Chronic spinal pain and physical–mental comorbidity in the United States: results from the national comorbidity survey replication. Pain. 2005;113:331-339.