From January to July, 2020, we searched databases on MEDLINE, Embase, Ovid, and Google using the key words “chronic pain”, “neuropathic pain”, “non-neuropathic pain”, “nociceptive pain”, “inflammatory pain”, “diffuse pain”, and “nociplastic pain”, cross-referenced with key words tailored for individual sections (eg, “cost-effectiveness”, “biopsychosocial”, “cancer”, etc) There were no restrictions on article types, date of publication, or language. For the pain management section, key words
SeriesChronic pain: an update on burden, best practices, and new advances
Introduction
It is difficult to overestimate the burden of chronic pain, which is defined by the International Association for the Study of Pain (IASP) as an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.1 Pain is the main reason why people seek medical care, with three of the top ten reasons being osteoarthritis, back pain, and headaches.2 Among the four leading causes of years lost to disability, three of these (back pain, musculoskeletal disorders, and neck pain) are chronic pain conditions.3 Prevalence rates of chronic pain vary between 11% and 40%, with a study by the US Centers for Disease Control and Prevention (CDC) estimating the point prevalence at 20·4%.4 A systematic review comprising studies done in the UK reported a pooled chronic pain prevalence rate of 43·5%, with the rate of moderate-to-severe disabling pain ranging from 10·4% to 14·3%.5 A large-scale 4-year longitudinal study, also done in the UK, found the annual incidence rate for chronic pain to be 8·3%, with a recovery rate of 5·4%.6
This paper is the first in a Series of three papers about chronic pain, and aims to provide an overview of chronic pain for a non-specialty audience, with emphasis on best practices and selected advances. The areas covered include epidemiology, the classification of pain, overarching models, and management, with the other articles focusing on nociplastic pain7 and neuromodulation,8 two areas that have witnessed substantial advances in the past several years but have not been adequately addressed in the general medicine literature.
Not all people are affected by chronic pain equally. Data from the CDC found higher prevalence rates in women, individuals from lower socioeconomic backgrounds, military veterans, and people residing in rural areas.4 Regarding race and ethnicity, studies are mixed, with some reporting the highest rates among non-Hispanic White people than any other group,4 whereas most have reported a higher prevalence in racial and ethnic minorities, such as African American people and indigenous populations.9 Explanations for racial differences include enhanced physiological pain sensitivity, cultural differences, and reduced access to care. When controlling for income amount and adverse life events, differences in prevalence are attenuated, but not eliminated.10 The prevalence of chronic pain and associated disability is higher in low-income countries than in high-income countries.11
The economic costs of chronic pain are substantial. A report by the Institute of Medicine, released in 2010, estimated that chronic pain afflicts approximately one in three Americans, costing between US$560 and US$635 billion per year in medical costs and lost productivity.10 This estimate did not include the cost of care for institutionalised individuals (such as prisoners or nursing home patients), military personnel, and children, or the costs associated with caregiving. A newer report found the average cost per year for one of the 15·4% of Australian people living with chronic pain to be AU$22 588–$42 979, when non-financial costs were considered.12
Section snippets
Chronic pain as a disease model
Acute pain is an unpleasant, dynamic psychophysiological process, usually in response to tissue trauma and related inflammatory processes; thus, this pain possesses a survival value and plays a role in healing. However, once the acute danger period has passed, the pain no longer becomes a necessity, but a burden—a disease unto itself.13 Although there is no clear threshold of when acute pain becomes chronic, it is generally accepted that pain persisting beyond the expected healing period (3
Biopsychosocial model and consequences of chronic pain
The biopsychosocial model postulates pain and disability as multidimensional, dynamic interactions among biological, psychological, and social factors that reciprocally influence each other (figure 1).17 It is generally accepted that characteristics such as depression, anxiety, poor sleep, and adverse social conditions can be the result of chronic pain, but it is less commonly known that these factors also predispose individuals to chronic pain. Psychological factors associated with the
Classification of pain and its importance
The categorisation of pain influences prognosis, work-up, and treatment at all stages, with implications for the provision of services (payer authorisation) and prevalence estimates. For example, in patients with back pain, in addition to red flags, which include severe or progressive neurological deficits (present in some patients with neuropathic pain), imaging is recommended when considering an invasive procedure, such as surgery or a cervical epidural steroid injection, which are more
Best practices
Published guidelines for chronic pain vary depending on whether they refer to the treatment of symptoms (neuropathic pain or back pain) or a condition (knee osteoarthritis), the perspective of the authors (eg, guidelines on knee osteoarthritis differ between surgical and non-surgical specialties),52, 53 and the methods of development. Although mechanism-based pain treatment is optimal, identifying the mechanisms behind the pain can be challenging or impossible in clinical practice, so treatment
Future avenues for research
Table 3 describes promising future research areas, ranging from advances in research methodologies, identifying neurobiological mechanisms, and emerging therapies. Evaluating pain treatments, particularly invasive ones, is challenging on multiple fronts. An important question concerns the optimum control comparator (ie, using invasive placebos, and whether or not true placebos are even possible for some interventions).130 For example, controlled studies evaluating epidural steroid injections
Search strategy and selection criteria
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