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4 How prevalent is pain and what are the common forms?

Pain is remarkably prevalent. It is present, at this moment, in millions across the globe. The specifics depend on factors including age, sex, ethnicity, and circumstance, but high pain prevalence is universal (Figure 4.1). In the U.S., data showed 116 million Americans, over one in three, experiencing pain: whether acute procedural pain, trauma, cancer, headache, low back pain, or other pain conditions (IOM 2011). Remarkably, a vast amount of pain is avoided: today millions of surgical procedures annually are performed with managed pain due to advances in surgical pain management and medication access worldwide (Chapter 30). Unfortunately, huge challenges persist in pain management as millions experience limited healthcare access and others struggle against chronic pain‐associated conditions. Here, we explore the challenges.

Figure 4.1 (a) Pain is highly prevalent, present in about 38% of the population. (b) Pain overall demonstrates some female preponderance. (c) Migraine, a common headache condition shows female preponderance, 2 : 1, female : male. (d) Cluster headache has a 2 : 1 male preponderance but is much less prevalent (0.1% lifetime prevalence for cluster headache; 14% lifetime prevalence for migraine).

The common causes of pain are well established and include: headache, low back pain, osteoarthritis, trauma, neuropathy, cancer, and HIV/AIDs primarily (Murphy et al. 2017). Some less common chronic pain conditions, such as CRPS and fibromyalgia, have particularly high healthcare utilization often leading clinicians to overestimate the relevance for education, are described elsewhere (Chapter 45).

Headache is highly prevalent worldwide with nearly half (47%) experiencing headaches at least annually. Most headaches are tension type headaches, 40% experience these. Migraines are less common but more disabling; women more affected than men with global lifetime prevalence (F : M) 22% : 10% and current prevalence 14% : 6% (Stovner et al. 2007). Low back pain is highly prevalent in many countries with 30–40% of adults reporting “current” back pain. Osteoarthritis is highly prevalent in older adults with 30% experiencing disabling pain due to arthritis, knee osteoarthritis has been noted as the most common cause of pain‐related impairment globally. Trauma‐related pain, including that related to musculoskeletal injuries is a universal phenomenon with extremely high life‐time prevalence, the extent of impairment from work due to musculoskeletal trauma (including back and sprain injuries) exceeds all other causes. Neuropathy is prevalent in older adults with 20% over age 75 impacted. Cancer pain is a global burden with 50% of advanced cancer patients reporting pain, access to pain medication is a major determinant in cancer‐related suffering. HIV/AIDS is associated with pain. Recognizing pain cause or basic mechanism is important in clinical practice as the choice of treatment depends on the source of pain and the potential risks of treatment vary with disease context.

Pain prevalence increases with age with 50% of older adults experiencing chronic pain. Much of this pain is due to degenerative joint disease: lumbosacral DJD, knee and hip osteoarthritis. Peripheral neuropathy increases with age. Shingles, a painful eruption of herpes zoster, can cause post‐herpetic neuralgia. The incidence of shingles is reduced by 50% with vaccination, CDC recommends vaccination for those age 60 and over.

Certain populations are especially prone to chronic pain, veterans, those of lower socioeconomic status, and former athletes. Patients with cancer are very likely to experience inadequately controlled pain.

The prevalence of pain varies somewhat between ethnic groups in the United States. Although pain thresholds (minimum detectable pain) are similar across ethnic groups, Caucasians generally demonstrate higher experimental pain tolerance than do African Americans, Hispanic, and Asian populations, the reasons are unknown (Kim et al. 2017). Important disparities in access to care and impacts on clinical decision‐making influence outcomes. These factors generally contribute to higher levels of untreated pain in minority populations (Campbell and Edwards 2012). There is no evidence that people of color experience less pain and proper pain assessment is essential for all patients.

Low socioeconomic status has a negative impact on pain outcomes and predicts a higher prevalence of pain in a population. Many factors may contribute to this especially physical work demands for patients with lower educational attainment and poor access to prompt and effective healthcare. For example, pharmacies located zip codes with lower incomes are less likely to stock opioid medications meaning that patients with cancer and other serious pain‐associated conditions cannot obtain WHO essential medications in their own neighborhoods (Green et al. 2005).

There are important, somewhat subtle, differences between how men and women respond to noxious stimuli in the laboratory, but similarities abound. In general, men and women respond to pain similarly and the differences between men and women are dwarfed by the interindividual variability in pain sensitivity that we don't yet have explanations for. Nonetheless women on average experience more pain than men. There are important sex differences in the prevalence in pain–associated conditions: migraines are much more prevalent in females and cluster headaches much more prevalent in males. There are also sex‐specific pain conditions such as dysmenorrhea, endometriosis, and testicular torsion.

Pain is an important cause of work‐related disability and being engaged in litigation or a workman's compensation claim has a negative impact on pain outcomes. Patients may not be conscious of secondary gain however pain persists when there is a matter pending legal resolution.

Finally, access to care is a major cause of persistent suffering. Over‐reliance on opioids has led to a backlash against assessing pain. In the U.S., opioids cause more overdose deaths than any other medication, in other countries, it is impossible to access opioids when clearly appropriate (Figure 4.2). Access to essential medicines, especially opioids is severely restricted in most countries globally so that countries with highest rates of opioid utilization report per capita consumption of 10 000 times more opioids than countries with the lowest rates. WHO estimates that 4.8 million people with cancer die in pain each year without medicine. Globally, millions are dying without relief from pain, there is a pain management crisis of epic proportions.

Figure 4.2 Access to pain‐relieving medication varies widely with location. This figure demonstrates that high‐resource countries have much higher opioid consumption that low‐resource countries.

Source: Berterame et al. (2016). © 2016, Elsevier.

References

1 Berterame, S., Erthal, J., Thomas, J. et al. (2016). Use of and barriers to access to opioid analgesics: a worldwide, regional, and national study. The Lancet 387 (10028): 1644–1656. http://www.thelancet.com/cms/attachment/2053462746/2060237771/gr2_lrg.jpg.

2 Campbell, C.M. and Edwards, R.R. (2012). Ethnic differences in pain and pain management. Pain Management 2 (3): 219–230.

3 Green, C.R., Ndao‐Brumblay, S.K., West, B., and Washington, T. (2005). Differences in prescription opioid analgesic availability: comparing minority and white pharmacies across Michigan. Journal of Pain 6 (10): 689–699. https://doi.org/10.1016/j.jpain.2005.06.002. PMID: 16202962.

4 Institute of Medicine (US) Committee on Advancing Pain Research, Care, and Education (2011). Relieving Pain in America: A Blueprint for Transforming Prevention, Care, Education, and Research. Washington, DC: National Academies Press.

5 Kim, H., Yang, G.S., Greenspan, J.D. et al. (2017). Racial and ethnic differences in experimental pain sensitivity: systematic review and meta‐analysis. Pain 158: 194–211.

6 Murphy, K., Han, J.L., Yang, S. et al. (2017). Prevalence of specific types of pain diagnoses in a sample of United States adults. Pain Physician 20: E257–E268.

7 Stovner, L.J., Hagen, K., Jensen, R. et al. (2007). The global burden of headache: a documentation of headache prevalence and disability worldwide. Cephalalgia 27: 193–210.