Understanding chronic pain

38% of adults reported chronic pain (pain that persisted for more than three months), in the Scottish Health Survey (2022). Chronic pain is more common in women, and with increasing age. It is associated with social deprivation, and with a history of adverse childhood experiences, among other factors⁶.

Chronic pain rarely occurs in isolation: 75% of people with chronic pain experienced at least one other long-term condition, and those with pain at three or more sites had an average of three other co-morbidities. These commonly include mental health disorders, heart disease and/or respiratory disease. Chronic pain can affect anyone, of any age, from any background, with or without other apparent ill health.

Everyone experiences pain, and can describe it intuitively, but may find it challenging to define. Pain 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.”

Pain

Based on IASP:

• Pain is always a personal experience that is influenced to varying degrees by biological, psychological and social factors.
• Pain and nociception are different phenomena. Pain cannot be inferred solely from activity in sensory neurons.
• Through their life experiences, individuals learn the concept of pain.
• A person’s report of an experience as pain should be respected.
• Although pain usually serves an adaptive role, it may have adverse effects on function and social and psychological well-being.
• Verbal description is only one of several behaviours to express pain; inability to communicate does not negate the possibility that a human experiences pain.

Chronic pain

Chronic pain is further categorised into:

• chronic primary pain
  • chronic pain in one or more anatomical regions that is characterised by significant emotional distress or functional disability, and that cannot be explained by another chronic condition. Examples include fibromyalgia, complex regional pain syndrome, non-specific low-back pain
• chronic secondary pain
  • cancer-related
  • post-surgical or post-traumatic
  • musculoskeletal
  • visceral
  • neuropathic
  • headache or orofacial pain

Assessment and treatment must always be person-centred and appropriate to the relevant clinical situations, though there are many commonalities between these groups.

An alternative, mechanistic, categorisation of pain that directly determines prescribing decisions is:⁷

1. Nociceptive pain: Pain arising from actual or threatened damage to non-neural tissue, and caused by activation of nociceptors
   • Pain from physical damage or potential damage to the body
2. Neuropathic pain: Pain arising as a direct consequence of a lesion or disease affecting the somatosensory system
   • Pain when an injury or medical condition damages the nervous system or prevents it from working properly
3. Nociplastic pain: Pain arising from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain
   • Pain that arises from altered sensation in the absence of damage to tissue or the nervous system

Note that an individual may experience two or more different types of pain, no matter how they are categorised.

Acute pain is generally present to provide a warning of danger, or notification of injury. It prompts us to take evasive or curative action and is therefore healthy and lifesaving. In contrast, the definition of chronic pain implies that, as pain has persisted beyond tissue healing time, it is a pathological condition, providing no useful purpose.

However, longer-term pain may be providing longer-term protection, prompting more gradual, sustained rehabilitation. Long-term pain is often associated with long-term tissue damage, as is the case with osteoarthritis.

Characteristics of chronic pain may arise before the three-month period has passed. Complex Regional Pain Syndrome, for example, has its onset soon after (often relatively minor) injury and is characterised by a heightened overall response to the pain.

Recent studies have shown that how individuals respond to acute pain is important in determining the longer-term experience. This response is influenced by:

• genetics
• other biological factors
• psychological factors, including previous experience of pain, stress, and childhood adversity⁶

The way in which acute pain is managed can have an important effect on long-term outcomes. This is clear, for example, in peri-operative care, where good, multi-modal post-operative analgesia is associated with reduced risk of chronic post-surgical pain and analgesia use. The British Pain Society state: “The principle of multimodal analgesia is that improved pain relief can be achieved by combining analgesics with different mechanisms of action that work synergistically” and “Multimodal analgesia also includes non-pharmacological elements, which may be low risk, have potential analgesic benefits and may reduce both the necessary dose and possible adverse effects of drugs used.”⁸ The postsurgical model is an important one to consider for the transition from acute to chronic pain.

In the peri-operative period, several factors are important when providing high-quality and effective pain relief and preventing long-term pain and analgesia use:

• Clear expectations, before surgery, of the likely extent and duration of pain can lead to healthier experiences and responses to post-operative pain
• Long-term analgesic use after surgery is influenced by the pattern of use during hospital care
• Clear expectations, after surgery, regarding the likely need, duration, and strength of analgesia will set realistic expectations for the individual after discharge from hospital
• Carefully-managed reduction and cessation of analgesic prescribing after discharge from hospital will reduce long-term use
• Placing an emphasis on functional recovery, which is facilitated by analgesia, will reduce the expected need for analgesics, and optimise quality of life

Good peri-operative pain relief in hospital is facilitated by appropriate staffing who understand the factors and are person-centred; a dedicated Pain Team is an effective way to address this need. A high-quality approach to planning, implementation and review of peri-operative analgesia supports good analgesic management. This facilitates good use of multimodal analgesia, including regional techniques where they are clinically indicated.

Effective and timely communication is key to successful pain management following discharge from hospital. This supports prompt, effective and equitable practice. Plans and expectations for analgesic management should be made clear and effectively communicated to both the individual and their GP. This may be facilitated by electronic prescribing systems which allow the expected duration of treatment to be described e.g. hospital electronic prescribing and medicines administration (HEPMA) bundles. Once a person has been discharged, ongoing communication between them and their care team can help optimise their recovery and guide further support as required.

Chronic pain can arise through many causes. These include:

• back pain (most common)
• arthritis, and other musculoskeletal diagnoses
• post-surgical pain
• diabetic neuropathic pain
• headaches
• fibromyalgia
• visceral pain (for example from endometriosis)

In many cases no definitive diagnosis can be reached.

The impact of chronic pain is extensive at the individual level, influencing all aspects of life and health⁹. This includes:

• physical and mental health
• the ability to work
• undertaking activities of daily living
• reduced physical activity
• negative effects on self-confidence, social functioning and self-identity

The relationship is often bi-directional - for example chronic pain can lead to depression, which heightens the experience of chronic pain.

There is also adverse impact on people's families, their work, the health services, and on society. In the United Kingdom it was estimated that primary care management of chronic pain accounted for 4.6 million general practice appointments per year, equivalent to 793 whole time general practitioners.

The medical model of treating pain – now considered insufficient in chronic pain – required diagnosis of the underlying cause and identification of the appropriate medicines to effect pain relief. The WHO Analgesic ladder was devised for treatment of cancer pain, and although widely used, was never validated in other types of pain. At the outset of treatment it is important that individuals with chronic pain and healthcare professionals recognise that complete relief of chronic non-cancer pain is often unrealistic. This issue led to the NHS campaign in England, Painkillers Don’t Exist. Even when effective analgesia can be achieved, more recent evidence suggests that it is not always the best thing – for example, anti-inflammatory medicines might actually cause chronic back pain by reducing the natural inflammatory/immune response in the acute phase. Breakthrough pain is associated with cancer, life-limiting conditions and end-of-life where background pain exists, and acute episodes of more severe pain may be experienced. In non-malignant chronic pain, the concept of breakthrough pain is poorly understood and it may not be a helpful concept to use.

A person-centred approach to pain management considers the biopsychosocial approach. This considers the person experiencing pain in the context of:

• their background (family, culture, occupation, financial circumstances, etc)
• their beliefs about pain and health
• fears
• expectations
• previous experiences of pain
• causes and its treatment
• other aspects of their physical and mental health

The goals of assessment and management are to understand the impact of pain on the person's life and for them to live as well as possible with the pain, balancing the potential harms of treatment with the potential benefits.

This requires multi-dimensional assessment, multi-disciplinary treatment approaches, and working in collaboration with the person in pain.

Identifying the clinical and social demographic factors associated with chronic pain may provide opportunities for prevention or early identification of risk with a view to minimising overall impact. This may offer limited help for individual patients, but could inform priorities in wider society, such as promoting reduction in health inequality.

As with any medicine, adverse effects of analgesics exist, and can outweigh benefits. Opioids are associated with a long list of potentially serious adverse effects that often limit their use. These include drowsiness, constipation, nausea, respiratory depression, immune dysfunction, dependency and sexual dysfunction, among many others. Both tolerance and the paradoxical phenomenon of opioid induced hyperalgesia can lead to escalating doses and harms while also actually making pain worse.

Opioids are associated with problematic substance use, dependency, and death, with opioid-related deaths in Scotland rising fourfold between 2000 and 2020. Prescribing rates of opioids are falling in Scotland (since publication of the SIGN Guideline, Management of Chronic Pain in 2013) and Scottish Government Quality Prescribing Guide for Chronic Pain 2018). However, this is gradual. Opioids remain an important cause of morbidity and mortality.

Gabapentinoids (gabapentin and pregabalin), indicated for treatment of neuropathic pain, were initially considered relatively safe. However, side effects are increasingly being recognised, including drowsiness or somnolence, dizziness, nausea, weight changes (abnormal appetite), cognition speech problems, ataxia and respiratory depression. These frequently limit their tolerability. 

Pregabalin can impact foetal development, and similar considerations may apply to gabapentin. Advice for health professionals can be found in the MHRA Pregabalin Drug Safety Update.

These medicines can be misused and are increasingly associated with drug-related deaths in Scotland¹⁰. Gabapentinoids are associated with serious long-term harms (including overdose and major trauma)¹¹.

Adverse effects of analgesics can be exacerbated by:

• polypharmacy (especially with opiates, other analgesics and/or sedatives)
• alcohol use
• smoking
• problematic substance use
• mental health conditions

There are additional risks arising through the use of non-prescribed analgesia, for example taking medicines that are prescribed for others, or sharing between family and friends or obtaining illicit drugs. In these cases, there is no opportunity to assess risks and therefore the likelihood of harm is greater.

All healthcare professionals should consider the risks of any prescribing, before prescribing decisions are made, in partnership with the individual. Any decisions need to be supported by early and ongoing review. The benefits and limitations of treating chronic pain with medication is discussed in more detail in Benefits and Limitations of treatment with medication.