1. Descriptive epidemiology of chronic pain
Epidemiological studies have demonstrated that, within the past month, around half us will have experienced an episode of pain which has lasted at least 1 day, with the most common sites reported, in a United Kingdom population study, being the low back (30%), hip (25%), neck and shoulder (25%) and knee (24%).9 Using a more stringent definition (suffered pain for 6 months, experienced pain in the last month and several times during the last week), a pan-European study reported a prevalence of 19%.1
Prevalence of chronic pain increases through adult life, reaching a peak around the seventh decade (eg, Ref. 5). Pain at some regional sites, particularly in the lower limb, increase in prevalence across the age range (eg, Ref. 12), whereas some such as low back pain decrease at older ages.3 Such a decrease has been hypothesised to be related to changes in pain perception, expectation of pain at older ages and comorbidities. Chronic pain may be related to premature mortality; a review of studies showed a relationship with cancer and cardiovascular death11 which may partly be related to lifestyle factors such as low levels of physical activity and poor quality diet.14
2. Early life factors in the aetiology of chronic pain
Early life factors have been linked to chronic pain in adulthood. Although retrospective studies are subject to recall bias, which has been shown to occur, long-term prospective studies demonstrate an increased risk of chronic pain in adulthood related to social environment in childhood (raised in care, death of a parent) as well as physically traumatic events such as premature birth, very low birth weight,8 and hospitalisation for a motor vehicle accident at young ages.6
3. Mechanisms mediating the relationship between early life factors and adult chronic pain
Clinical studies have demonstrated that physical stresses (eg, preterm birth) result in altered function of the stress-response axis and such perturbations are still present at age 18 months.4 Amongst preterm infants, neonatal procedure-related stress predicted cortisol levels at age 7 years.2 This gave rise to the hypothesis that among persons experiencing “stressful” early life events, altered function of the Hypothalamic–Pituitary–Adrenal axis may be an important mediator of pain onset, and this has been confirmed in a prospective population-based study.10 Risk is likely to involve both genetic and environmental effects although it is likely that many genes, all with small effects, will be involved.15
4. Predicting outcome of an episode pain
A key issue for epidemiologists is identifying, amongst those with a new episode of pain, in whom the pain is likely to become chronic. Focussing early management on these people is likely to optimise cost effectiveness of management approaches. A review of factors preceding transition from acute to chronic pain identified clinical factors, older age, and mood as the factors with strongest evidence for long-term disability or work absence,13 and tools such as the Orebro Screening Questionnaire seek to capture such factors (and wider psychosocial factors) in terms of predicting risk of poor outcome.7
. Breivik H, Collett B, Ventafridda V, Cohen R, Gallacher D. Survey of chronic pain in Europe: prevalence, impact on daily life, and treatment. Eur J Pain 2006;10:287–333.
. Brummelte S, Chau CM, Cepeda IL, Degenhardt A, Weinberg J, Synnes AR, Grunau RE. Cortisol levels in former preterm children at school age are predicted by neonatal procedural pain-related stress. Psychoneuroendocrinology 2015;51:151–63.
. Dionne CE, Dunn KM, Croft PR. Does back pain prevalence really decrease with increasing age? A systematic review. Age Ageing 2006;35:229–34.
. Grunau RE, Haley DW, Whitfield MF, Weinberg J, Yu W, Thiessen P. Altered basal cortisol levels at 3, 6, 8 and 18 months in infants born at extremely low gestational age. J Pediatr 2007;150:151–6.
. Johannes CB, Le TK, Zhou X, Johnston JA, Dworkin RH. The prevalence of chronic pain in United States adults: results of an Internet-based survey. J Pain 2010;11:1230–9.
. Jones GT, Power C, Macfarlane GJ. Adverse events in childhood and chronic widespread pain in adult life: results from the 1958 British Birth Cohort Study. PAIN 2009;143:92–6.
. Linton SJ, Boersma K. Early identification of patients at risk of developing a persistent back problem: the predictive validity of the Orebro Musculoskeletal Pain Questionnaire. Clin J Pain 2003;19:80–6.
. Littlejohn C, Pang D, Power C, Macfarlane GJ, Jones GT. Is there an association between preterm birth or low birthweight and chronic widespread pain? Results from the 1958 Birth Cohort Study. Eur J Pain 2012;16:134–9.
. Macfarlane GJ, Beasley M, Smith BH, Jones GT, Macfarlane TV. Can large surveys conducted on highly selected populations provide valid information on the epidemiology of common health conditions? an analysis of UK Biobank data on musculoskeletal pain. Br J Pain 2015;9:203–12.
. McBeth J, Silman AJ, Gupta A, Chiu YH, Ray D, Morriss R, Dickens C, King Y, Macfarlane GJ. Moderation of psychosocial risk factors through dysfunction of the hypothalamic-pituitary-adrenal stress axis in the onset of chronic widespread musculoskeletal pain: findings of a population- based prospective cohort study. Arthritis Rheum 2007;56:360–71.
. Smith D, Wilkie R, Uthman O, Jordan JL, McBeth J. Chronic pain and mortality: a systematic review. PLoS One 2014;9:e99048.
. Urwin M, Symmons D, Allison T, Brammah T, Busby H, Roxby M, Simmons A, Williams G. Estimating the burden of musculoskeletal disorders in the community: the comparative prevalence of symptoms at different anatomical sites, and the relation to social deprivation. Ann Rheum Dis 1998;57:649–55.
. Valentin GH, Pilegaard MS, Vaegter HB, Rosendal M, Ørtenblad L, Væggemose U, Christensen R. Prognostic factors for disability and sick leave in patients with subacute non-malignant pain: a systematic review of cohort studies. BMJ Open 2016;6:e007616.
. Vandenkerkhof EG, Macdonald HM, Jones GT, Power C, Macfarlane GJ. Diet, lifestyle and chronic widespread pain: results from the 1958 British Birth Cohort Study. Pain Res Manag 2011;16:87–92.
. Zorina-Lichtenwalter K, Meloto CB, Khoury S, Diatchenko LB. Genetic predictors of human chronic pain conditions. Neuroscience 2016. pii: S0306-4522(16) 30126–9.