Understanding Pain

The fundamentals of pain

Pain is defined as an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.¹ Pain has many dimensions and can vary in intensity, location in the body and duration of time. Depending on the type of pain, it can feel like throbbing, burning, shooting or tingling and can range in intensity from mild to severe.^3,4 In addition to the physical impact, it can also have psychological, emotional and social effects on everyday life.³

Sometimes the cause of pain is obvious, such as from injury, and other times the source might come from an underlying condition. In some cases, it can be difficult to categorise the exact cause of pain.³

What happens in the body when we encounter a harmful stimulus?

Pain is a normal response to actual or potential injury to the body but can also occur without a clear cause:^3,5,6

The three different mechanisms that can lead to the perception of pain: Harmful stimuli, Signal, Pain is felt

There are three different mechanisms that can lead to the perception of pain. In some cases, more than one mechanism may be involved.

1. Nociceptive pain

This type of pain is typically caused by damage to the body’s tissues from either injury or inflammation. Examples include:^5,7,8

Sports injury
Arthritis
Appendicitis

2. Neuropathic pain

This type of pain is typically caused by damage to nerves. This damage can be due to lesions in the nervous system, diseases that affect the nerves or injury. Examples include:^3,5,9

Peripheral neuropathic pain e.g., painful diabetic peripheral neuropathy, chemotherapy-induced neuropathy
Post-stroke pain
Spinal cord injury
Cancer-induced neuropathic pain

3. Nociplastic pain

This type of pain occurs without clear evidence of actual or threatened tissue damage or lesions and diseases of the nervous system. Examples include:¹⁰

Fibromyalgia
Complex regional pain syndrome
Non-specific back pain

What is the difference between acute and chronic pain?

Pain is complex and is not only classified by the mechanisms above, but also by severity, location in the body and duration.² One of the most common ways to classify pain is by the duration of time someone has been experiencing pain:

Acute Pain	Chronic Pain
Lasts for less than 3 months¹¹	Lasts for longer than 3 months¹²
Occurs usually in response to tissue trauma and related inflammatory processes¹³	Can be due to an underlying disease such as cancer or arthritis³ OR Has no obvious cause⁵ or may continue after the original injury has healed³
Serves a useful and life sustaining (protective) function¹⁴	Typically serves no adaptive purpose⁵
Poorly controlled acute pain can be a factor leading towards chronic pain¹⁵	Influenced by a number of interconnected factors, including:¹³ Biological: genetics, age, sex, sleep, hormones and internal pain regulation systems Psychological: poor sleep, anxiety or depression Sociocultural: low educational attainment, culture and poor social support

In 2019 the IASP and the World Health Organization recognized chronic pain as a health condition in its own right¹³

Some of the most common types of chronic pain are:¹⁶

Migraine
Low back pain or lumbar pain
Neck pain
Musculoskeletal pain
Pain associated with osteoarthritis

Who is affected by chronic pain?

Chronic pain is an enormous global health problem¹⁷ and affects around 1 in 5 adults worldwide.^18,19,20

What are some factors that can increase the likelihood of experiencing chronic pain?^13,21,22,23

Factors that can increase the likelihood of experiencing chronic pain: Age

Chronic pain becomes more common with increasing age.²¹

Factors that can increase the likelihood of experiencing chronic pain: Sex

Women are more likely to report or experience chronic pain than men²² and report a higher level of pain intensity and higher pain-related disability than men²³

Factors that can increase the likelihood of experiencing chronic pain: Sociocultural background

Chronic pain is associated with low educational attainment, culture and poor social support¹³

Pain is a dynamic consequence of a host of biological, psychological, and social factors; hence, guidelines have recommended interdisciplinary treatment, which ideally makes use of a personalised approach with a shared decision-making.¹³

The serious impact of chronic pain

Chronic pain exerts an enormous personal and economic burden, and it is considered to be one of the main causes of disability:^13,19

90%

Up to 90% of adults with chronic pain experience clinically significant insomnia²⁴

54%

of patients with chronic pain are less able or unable to do household chores²⁵

30%

of chronic pain patients have difficulty maintaining an independent lifestyle²⁵

27%

of patients with chronic pain have relationship difficulties²⁵

Mental Wellbeing:

Chronic pain can have a significant impact on mental health and wellbeing.¹³ Research has shown that more than 50% of patients with chronic low back pain have depression and anxiety,²⁶ and people suffering from chronic musculoskeletal pain with both depression and anxiety are likely to experience more severe pain and pain-related disability.²⁷

The Economy:

The cost of chronic pain is significant:^13,19,28,29

635

Chronic pain affects 1 in 3 Americans, costing up to $635 billion per year²⁸

Europe

300

Across Europe, the cost of chronic pain is estimated to be as high as €300 billion

Chronic pain also increases the risk of other health problems and social exclusion.³⁰

Employment:

Chronic pain affects people’s ability to do their jobs effectively.

In the US, people with chronic pain worked 7.5 days less than those without chronic pain.³¹
In the EU, more than 50% of people are prevented from doing their work because of chronic pain.³²
In the EU, chronic pain has substantial negative impacts on productivity at work.³²

Having chronic pain may also affect employment. A survey revealed that less than 20% of people with chronic pain receive occupational rehabilitation in order to remain at work.³² Additionally, research in the UK found that chronic pain was present in 79% of those who were unable to work because of ill health and only in 40% of those in paid employment.³³

References
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²Stanos S, et al. Postgrad Med. 2016;128(5):502-515.
³Orr PM, et al. Crit Care Nurs Clin N Am. 2017;29:407–418.
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⁵National Pharmaceutical Council. Pain: Current Understanding of Assessment, Management, and Treatments. 2001. Available at: https://www.npcnow.org/sites/default/files/media/Pain-Current-Understanding-of-Assessment-Management-and-Treatments.pdf. Accessed May 2022.
⁶Yam MF, et al. Int J Mol Sci. 2018;19(8):2164.
⁷Igolnikov I, et al. Chapter 39, Handbook of Clinical Neurology. 2018:423–430.
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¹¹World Health Organization (WHO). International Classification of Diseases 11th Revision (ICD-11). MG31 Acute pain. 2019. Available at: https://icd.who.int/browse11/l-m/en#/http%3a%2f%2fid.who.int%2ficd%2fentity%2f1404135736. Accessed May 2022.
¹²World Health Organization (WHO). International Classification of Diseases 11th Revision (ICD-11). MG30 Chronic pain. 2019. Available at: https://icd.who.int/browse11/l-m/en#/http://id.who.int/icd/entity/1581976053. Accessed May 2022.
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²⁸U.S. Department of Health and Human Services. Pain Management Best Practices Inter-Agency Task Force Report: Updates, Gaps, Inconsistencies, and Recommendations. 2019. Available at: https://www.hhs.gov/sites/default/files/pmtf-final-report-2019-05-23.pdf. Accessed May 2022.
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³¹Yong RJ, et al. Pain. 2022;163(2):e328–e332.
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³³Macfarlane G, et al. Br J Pain. 2015;9:203–212.