Pain and pain relief

Introduction^{2 3 4}

• Pain may be defined as an unpleasant sensory or emotional experience associated with actual or potential tissue damage.

• Chronic pain is defined as pain still present after three months despite appropriate treatment.

• Breakthrough pain is defined as pain of moderate or severe intensity occurring against a background of controlled chronic pain.

• Emotional, environmental and social factors are becoming increasingly recognised as issues which need to be addressed in the management of chronic pain.

Chronic primary pain has no clear underlying condition or the pain or its impact is out of proportion to any observable injury or disease. All forms of pain can cause distress and disability, but these features are particularly prominent in presentations of chronic primary pain.²

Fibromyalgia (chronic widespread pain) is a type of chronic primary pain. The WHO disease classification ICD-11 also categorises complex regional pain syndrome, chronic primary headache and orofacial pain, chronic primary visceral pain and chronic primary musculoskeletal pain as types of chronic primary pain.⁵

In chronic secondary pain, an underlying condition adequately accounts for the pain or its impact.

Take an adequate history²

Pain is often mistreated or undertreated and can lead to depression, insomnia, lethargy and reduced physical and mental functioning. Successful control is more likely to be achieved if a proper assessment is made, which should include:

• The site of the pain.

• The duration, speed of onset and whether the pain is intermittent or constant.

• The character of the pain - this will indicate whether it is neuropathic or nociceptive, somatic or visceral.

• Aggravating and relieving factors.

• Impact on daily living.

• Social, emotional and psychological aspects.

• Severity - use of pain scales can make this more objective.⁶

The analgesic ladder^{4 7 8 9 10}

The successful drug management of pain relies on selecting the appropriate drug at the correct dosage and balancing efficacy against adverse effects. For this reason, the World Health Organization introduced the concept of the analgesic ladder. This has served its purpose well.

However, increased survival rates in cancer and advances in the management of pain have made it less relevant in some circumstances. For example, new formulations of drugs such as nasal sprays and sublingual tablets and the increasing use of adjuvant therapy to reduce the amount of opioid have widened the options available for pain management. See the separate article Pain Control in Palliative Care for more details.

Oral analgesics are usually used first-line.

• Step one - non-opioid analgesics (eg, aspirin, paracetamol, non-steroidal anti-inflammatory drugs (NSAIDs)). If anticipation of pain can be abolished, it may not be necessary to step up to opioids. Give non-opioids regularly and use adjuvants if necessary.

• Step two - mild opioids (eg, codeine) with or without non-opioid:
  

  • Codeine - effective for the relief of mild-to-moderate pain but is too constipating for long-term use.

  • Dihydrocodeine - efficacy similar to codeine. Can be given four-hourly. Doses may need to be adjusted individually according to the degree of analgesia and side-effects. If necessary, step up to morphine, or fentanyl (to initiate, consider involving a specialist in palliative care). Arrange for doses to be given at regular intervals - 'by the clock', rather than 'as required', using the oral route whenever possible.

• Step three - strong opioids with or without non-opioid:
  

  • Useful for moderate-to-severe pain, particularly of visceral origin. Long-term prescribing is most common for palliative care in malignant disease but also may be appropriate for chronic non-malignant conditions, in conjunction with specialist advice.

  • One of the main reasons patients in severe pain do not receive adequate analgesia is fear of addiction. If the condition is terminal cancer, this is not an appropriate concern.

  • See also the separate article on Opioid Analgesics.

Adjuvant therapy^{2 8 11}

• Antidepressants - low-dose antidepressants (eg, amitriptyline 75-150 mg nocte) are useful for controlling neuropathic pain. See separate article Neuropathic Pain and its Management for more details.

• Anticonvulsants, most commonly carbamazepine, are also useful for neuropathic pain although they have performed inconsistently in random controlled trials. Gabapentin and pregabalin are also licensed for this use. Their main indication is in diabetic neuropathy and trigeminal neuralgia but, also, in shooting pain which does not respond to antidepressants - eg, phantom limb pain.

• Muscle spasm - consider a muscle relaxant such as diazepam or baclofen.

• Nerve compression may be reduced by a corticosteroid such as dexamethasone, which reduces oedema around the tumour, thus reducing compression.

• N-methyl-D-aspartate (NMDA) receptors in the postsynaptic area of the neuron have a role in the conduction of pain and NMDA receptor agonists, such as ketamine and methadone, may be useful adjuncts in pain control.

• NICE recommends a group exercise programme to manage chronic primary pain, and to encourage people with chronic primary pain to remain physically active
  for longer-term general health benefits.

• NICE also recommends considering acceptance and commitment therapy (ACT) or cognitive behavioural therapy (CBT) for chronic primary pain.

Physical methods^{8 12}

Reversible

• Local anaesthetics:
  

  • Block nerve conduction reversibly.

  • Frequent blocks sometimes effect a permanent cure.

  • Regional blocks have been used to good effect in shoulder pain, intercostal neuralgia, postoperative scar pains and other peripheral neuralgias.

• Epidural steroids and facet joint blocks:
  

  • Commonly used for chronic back pain.

  • Trials show statistically significant improvement for up to one year.

  • It is not known whether addition of steroid to local anaesthetic is essential. There is supportive evidence for this combination in the control of pain from disc herniation and spinal stenosis.¹³

  • Better results are obtained the earlier the patient is treated and in patients who have not had spinal surgery.

  • It may take up to a week for benefit to be felt.

  • They are worth repeating if there is short-lived relief and a course of three injections is often recommended.

  • Facet joint injection with local anaesthetic and steroid is indicated when pain is worse when sitting and pain is provoked by lateral rotation and spinal extension.

• Electrical physical modalities for chronic primary pain .

• Acupuncture - NICE recommends a single course of acupuncture or dry needling, within a traditional Chinese or Western acupuncture system, to manage chronic primary pain.²

Irreversible

• Neurolytic blocks - aimed at destroying nerves conducting pain by cutting, burning or damaging. Plasticity theory counsels against this approach due to the ability of the CNS to 'rewire'. The evidence base supporting their use in cancer pain is limited. However, there are a large number of positive anecdotal reports and they still have a place in cancer pain, principally when there is short prognosis or where alternatives are not helping or possible.¹⁴

• Surgery:

  • Specific examples where surgery may be appropriate include the internal fixation of pathologically fractured long bones, the stabilisation of vertebral fractures and the construction of a shunt to drain progressive ascites into the superior jugular vein.

  • Neurosurgical interventions are often used for orthopaedic pain.¹⁵ The effectiveness of dorsal column stimulation has improved with advances in technology.¹⁵

  • There is renewed interest in destructive procedures such as rhizotomy, cordotomy and dorsal root entry zone (DREZ) lesions in the management of cancer pain but further research is needed.¹⁶

Radiotherapy⁸

Systemic radioisotope therapy may be useful in controlling pain from bone metastases.

Chemotherapy⁸

Whilst many cancers become chemotherapy-resistant in the latter stages, multiple myeloma and small cell lung cancer retain their sensitivity and this can be exploited in the control of pain from bone metastases.

Hormone therapy⁸

Anti-oestrogen therapy for breast cancer can have a major effect on the control of pain from metastatic disease.¹⁷ Anti-androgen therapy is effective in controlling the pain from metastatic prostate disease but its effectiveness in localised prostate cancer require further research.¹⁸

Bisphosphonates⁸

These are increasingly used to control metastatic bone pain in a variety of cancers. They do not, however, inhibit the development of new metastases. Drugs such as denosumab and the use of radionuclides are currently being explores in this respect.¹⁹

Alternative methods⁸

• Chiropractic - randomised controlled trials support the use of this discipline in the management of acute and chronic neck pain and acute and chronic low back pain.^{20 21}

• Physiotherapy - popular and economically viable but limited long-term success demonstrated in systematic reviews.

• Complementary medicine - homeopathy, hypnosis and herbal treatments - lack of controlled clinical trials but found helpful by some patients.²²