Management of

chronic pain
 DEFINITION OF PAIN
 Everyone has experienced pain, but it has been difficult to define
this sensation satisfactorily.
 One description is 'what the patient says hurts'.
 The International Association for the Study of Pain (IASP) defines pain
as 'an unpleasant sensory and emotional experience associated
with actual or potential tissue damage, or described in terms of such
damage'.
 This definition emphasizes that pain is not only a physical sensation
but also, ultimately, a subjective psychological event.
 It accepts that pain can occur in spite of negative physical findings
and investigations.
 Pain has sensory, cognitive and motivational-affective dimensions
and has been described as a biopsychosocial experience as this
must be taken into account when assessing and planning a
treatment strategy for the patient with pain.
CLASSIFICATION OF PAIN

 Pain may be classified according to aetiology.

 NOCICEPTIVE PAIN:
 Nociceptive pain results from tissue damage causing continual
nociceptor stimulation. It may be either somatic or visceral in origin.
 Somatic pain:
 Somatic pain results from activation of nociceptors in cutaneous
and deep tissues, such as bone. Typically, it is well localized and
described as aching, throbbing or gnawing. Somatic pain is usually
sensitive to opioids.
Visceral pain

 Visceral pain arises from internal organs. It is characteristically vague

in distribution and quality and is often described as deep, dull or
dragging.
 It may be associated with nausea, vomiting and alterations in
arterial pressure and heart rate.
 Stimuli, such as crushing or burning, which are painful in somatic
structures often evoke no pain in visceral organs.
Mechanisms of visceral pain include abnormal distension or
contraction of smooth muscle, stretching of the capsule of solid
organs, hypoxia or necrosis and irritation by algesic substances.
Visceral pain is often referred to sites distant from the visceral lesion.
One example of this is shoulder pain resulting from diaphragmatic
irritation
NEUROPATHIC PAIN

 Neuropathic pain is caused by functional abnormality of the

peripheral and/or central nervous system.
 It is characteristically dysaesthetic in nature and patients complain
of abnormal sensations. There may be marked allodynia, i.e. a
normally non-painful stimulus, such as light touch, provokes pain.
Pain may be described as shooting or burning and may occur in
areas of numbness. Neuropathic pain may develop immediately
after nerve injury or after a variable interval. It is often persistent and
relatively resistant to opioids. There is a tendency for a favourable
response to centrally modulating medication, such as
anticonvulsants and tricyclic antidepressants.
 There are many causes of neuropathic pain. Central pain is
associated with lesions of the central nervous system, such as
infarction and trauma.
Lesions in the peripheral nervous system include peripheral nerve
injuries, peripheral neuropathies and tumour infiltration.
Sympathetically maintained pain

 Pain that is maintained by sympathetic efferent innervation or by

circulating catecholamines is termed sympathetically maintained
pain (SMP).
 Sympathetic nerve block provides at least temporary reduction of
pain, but current thinking is that this does not imply a mechanism
for the pain.
 Thus, the condition previously termed 'reflex sympathetic dystrophy'
has now been renamed 'complex regional pain syndrome type I', as
not all patients with this clinical diagnosis have relief of pain
following sympathetic nerve block.
Complex regional pain syndrome
(CRPS) type I
 is a syndrome that can develop in a limb after mild soft tissue trauma or
a fracture.
 The pain is characteristically burning in nature and associated with
allodynia (abnormal sensitivity of the skin). It is associated at some point
with swelling, abnormal sweating and changes in skin blood flow.
 Atrophy of the skin, nails and muscles can occur and localized
osteoporosis may be demonstrated on X-ray or bone scan. Movement
of the limb is usually restricted as a result of the pain and contractures
may result.
 Treatment is directed at providing adequate analgesia to encourage
active physiotherapy and improvement of function. In cases with
sympathetically maintained pain, sympathetic nerve block may be part
of this treatment strategy.
 Complex regional pain syndrome type II:
 is a condition that has the features described above, but which
occurs after partial injury of a nerve or one of its branches.
SOMATOFORM PAIN DISORDER

 This is a currently accepted psychiatric diagnosis, which can be

used when there is substantial evidence that psychological factors
are judged to have an important role in the onset, exacerbations or
maintenance of the pain.
 Strict diagnostic criteria must be fulfilled before such a diagnosis
can be made and this should be made by or in conjunction with a
psychiatrist.
PAIN MANAGEMENT CLINIC

 ASSESSMENT
 Comprehensive assessment of patients with pain is a vital first step. Pain
is a generally a symptom rather than a disease. Efforts should be made
to investigate, diagnose and, if possible, treat the underlying cause of
the pain before using empirical pain-relieving techniques.
 Patients attending a pain management clinic may be referred by either
their hospital consultant or their GP.
 The key elements of a pain history should be ascertained using a
structured interview. Assessment should include:
• location, verbally or using a pain diagram
• mode of onset and frequency
• aggravating factors
• relieving factors
• quality, e.g. burning, shooting - use McGill Pain Questionnaire
 intensity, e.g. verbal rating scale, visual analogue scale, faces
pain scale (children)
• previous treatments
• concurrent medical illnesses
• current medication (analgesics and others)
• basic psychological/psychiatric assessment
• patient's own ideas as to causation
• impairment and disability.
 Basic psychological assessment can be made by the clinician,
sometimes aided by questionnaires.
 Levels of anxiety, depression and coping ability are some of the
elements that can be measured using appropriate tools.
 If full psychological evaluation is indicated, it should be performed
either by a psychiatrist or by a clinical psychologist, preferably one
who is an integral member of the pain management team
 Chronic pain affects not only the patient, but also the family.
 Patients with chronic pain become depressed, anxious and
medication-dependent.
 They lose their jobs, financial security and social status.
 Their relationships deteriorate.
 Interviewing of the patient’s relatives or close friends may be
important in assessing the impact of the pain on family dynamics
and lifestyle.
METHODS OF MANAGEMENT OF
CHRONIC PAIN
 MEDICATION
 Many patients in pain are prescribed analgesic drugs.
 The pharmacology of these agents is fully discussed elsewhere and
only aspects of particular relevance to their use in chronic pain are
mentioned below.
Non-steroidal anti- inflammatory
drugs
 Non-steroidal anti-inflammatory drugs (NSAIDs) interfere with the
production of prostaglandins and prostacyclins by inhibiting the
enzyme cyclooxygenase.
 They possess analgesic and anti-inflammatory action and are used
widely in the management of mild to moderate pain, particularly of
somatic origin.
 They may be very effective for painful bone metastases and useful
in dysmenorrhoea, arthritis and musculoskeletal pain.
 They may be used orally or as a suppository.
 Side-effects may be a problem, especially in the elderly.
Opioid analgesics

 Cancer pain
 Approximately 70% of patients with advanced cancer develop
significant pain before death. Most cancer pain responds to
pharmacological measures and successful treatment is based on
simple principles that have been promoted by the World Health
Organization and are extensively validated. Analgesic drugs should
be taken 'by mouth', 'by the clock' (i.e. regularly) and 'by the
analgesic ladder’.
 Cancer pain is continuous and medication must be taken regularly.
It is given orally unless intractable nausea and vomiting occur or
unless there is a physical impediment to swallowing.
 The first step on the 'analgesic ladder' is a non-opioid, such as
paracetamol, aspirin or an NSAID.
 If this is inadequate, a weak opioid such as codeine is added.
 The third step is substitution of the weak opioid by a strong opioid.
Inadequate pain control at one level requires progression to drug
on the next level, rather than to an alternative of similar efficacy.
Adjuvant analgesics, such as tricyclic antidepressants or
anticonvulsants, may be used at any stage.
 Morphine is the strong oral opioid of choice. Immediate-release oral
morphine, either as a liquid or in tablet form, is given every 4h, if
necessary in increasing dosage, until pain is controlled.
 When the required daily dose has been established, it is usual to
convert to sustained-release morphine tablets, which need to be
taken only once or twice daily.
 In addition, immediate-release morphine elixir or tablets should be
prescribed for breakthrough pain.
 The dose of morphine necessary to treat breakthrough pain is one-
sixth of the total daily morphine requirement.
Alternative opioids and alternative
routes of administration

 Hydromorphone is an alternative opioid, it is used orally and is more

potent than morphine, with 1.3 mg of hydromorphone being
equivalent to 10 mg of morphine.
 When administered orally, hydromorphone reaches its peak effect
more rapidly than morphine and has a slightly shorter duration of
action.
 Immediate-release and sustained-release preparations are
available. Hydromorphone is normally used if morphine is not
tolerated.
 Methadone is a potent opioid analgesic and also an N-methyl-D-
aspartate (NMDA) receptor antagonist.
 Methadone is absorbed rapidly by the oral route and has a long
half-life that may range from 13 to 51 h.
 Initial dosing must be monitored carefully as relatively small doses of
methadone may be needed in comparison with the previous opioid
dose.
 Methadone should be considered a third-line drug indicated for
cancer pain that appears poorly responsive to morphine,
diamorphine, fentanyl or hydromorphone in spite of dose escalation
and the use of adjuvant drugs.
 Methadone is available as tablets, linctus and injection.
 If a patient is unable to take medication by mouth, there are various
alternative routes for opioid administration.
 A transdermal drug delivery system has been developed for
fentanyl. Fentanyl patches are stuck onto the skin and drug from the
reservoir diffuses through the rate-controlling membrane and forms
a subcutaneous depot from which the drug is taken up into the
circulation.
 Continuous subcutaneous administration is another alternative
method of administration if oral medication cannot be taken.
 A small portable battery-operated syringe driver fitted with a 20 ml
syringe containing the total daily opioid dose is usually used.
 Morphine suppositories are available for rectal administration.
 Opioids can be administered spinally, either epidurally or
intrathecally, for:
patients whose pain is controlled effectively by oral opioids but who
suffer intolerable unacceptable side-effects, such as drowsiness or
vomiting.
• patients whose pain cannot be controlled by the use of oral or
systemic opioids.
 Non-cancer pain
 Weak opioid drugs, e.g. dihydrocodeine, are useful for moderate
pain.
 However, they may be taken in excess, and often with only little
benefit, by the patient with chronic non-malignant pain.
 Treatment in the pain management clinic may involve weaning the
patient off such medication.
 The use of strong opioids in non-malignant pain is controversial.
 There is conflict about whether opioids are effective and whether or
not they are safe.
 There is some evidence that opioids relieve pain and improve
function in patients with non-cancer pain.
Adjuvant analgesics

 These are drugs that have primary indications other than pain but are
analgesic in some painful conditions.
 Oral corticosteroids:
 The mechanism by which corticosteroids produce analgesia is
unknown.
 They reduce inflammatory mediators, specifically prostaglandins.
 They reduce peritumour oedema in neoplastic tissue, thus relieving pain
by reducing pressure on adjacent pain-sensitive structures.
 They are administered for cerebral metastases, spinal cord
compression, superior vena caval compression and neural infiltration or
compression.
 In addition, they are prescribed for their euphoric effect and to
stimulate appetite for patients with cancer.
Anticonvulsants

 Anticonvulsants are used in the treatment of neuropathic pain.

 The precise mechanism of action is unclear. They have a stabilizing
effect on neuronal cell membranes, possibly by inactivation of
sodium channels.
 They may also facilitate GABA (y-aminobutyric acid)-mediated
inhibition and decrease activation of NMDA receptors. Gabapentin,
carbamazepine and phenytoin have a product licence for use in
neuropathic pain and trigeminal neuralgia.
 Sedation and ataxia are common side-effects of some of these
drugs and may limit dose escalation, especially in the elderly.
Serious complications (mainly haematological) may occur.
 Tricyclic antidepressants
 Tricyclic antidepressants have an important role in the management
of pain, independent of their effect on mood.
 Tricyclic drugs reduce the reuptake of the amine neurotransmitters
norepinephrine and 5-hydroxytryptamine into the presynaptic
terminal, increasing the concentration and duration of action of
these substances at the synapse and thereby enhancing activity in
the descending inhibitory pain pathway.
 Amitriptyline is the commonest tricyclic drug prescribed as an
analgesic
 Antiarrhythmic drugs
 Systemic local anaesthetic infusions have been used diagnostically
and therapeutically for chronic neuropathic pain.
 Lidocaine 5mg kg-1 given intravenously to patients with painful
diabetic peripheral neuropathy in a double-blind cross-over study
has been demonstrated to produce analgesia. Unfortunately, the
effect is short-lived.
 Oral mexiletine has been used successfully in diabetic peripheral
neuropathy.
 Ketamine
 Ketamine is an NMDA receptor antagonist; it has been used
successfully as an analgesic via intravenous, subcutaneous and oral
routes. Psychometric side-effects may be a problem.
 Capsaicin cream
 Capsaicin is an alkaloid derived from chillies. It depletes substance P
in local sensory nerve terminals. Local application may alleviate
pain in painful diabetic peripheral neuropathy, osteoarthritis and
psoriasis. It has also been suggested for postherpetic and
intercostobrachial neuralgia.
NEURAL BLOCKADE IN PAIN
MANAGEMENT
 Nerve blocks have been performed for many years in the
management of pain.
 A nerve block comprises an injection of a local anaesthetic
(sometimes combined with steroid) or a neurolytic agent around a
peripheral or central sensory nerve, a sympathetic plexus or a trigger
point.
 Correct use of nerve blocks in the treatment of chronic pain
requires an experienced practitioner with a thorough knowledge of
anatomy and an understanding of pain syndromes.
 Local anaesthetics
 Local anaesthetics have been injected into muscle trigger points for
the relief of myofascial pain and it has been shown that prolonged
relief of pain can result from a series of local anaesthetic blocks to
peripheral nerves.
 It is unclear why pain relief may persist after the duration of
pharmacological action.
Corticosteroids

 Corticosteroids have been shown to block transmission in normal

unmyelinated C fibres and to suppress ectopic neural discharges in
experimental neuromas.
 They are sometimes added to local anaesthetics when injected
into trigger points, typically those in painful points.
 Epidural steroids
Epidural steroids have been used since 1962 for nerve root pain.
 Lumbar and cervical facet blocks
 Chronic back and neck pain are common complaints in pain
management clinics. Lumbar and cervical facet joints have been
considered to be potential sources. Injections of steroid into both
lumbar and cervical facet joints are commonly perform procedures,
although there is controversy about long-term benefit.
 Radiofrequency lesions of the facet nerves have been suggested
for longer-term relief.
Sympathetic nerve blocks

 Visceral nociceptive afferents travel in the sympathetic nervous

system to the spinal cord. Visceral pain tends to be less opioid
sensitive than somatic pain. Percutaneous sympathetic blocks may
therefore be useful in the management of severe cancer-related
visceral pain that is poorly controlled with opioids or controlled only
with intolerable side-effects.
 Phenol or alcohol may be used.
 E.g. coeliac, superior hypogastric, inferior hypogastric, lumbar
sympathetic and cervical ganglion block.
Neurolytic techniques

 Neural destruction can be produced with alcohol, phenol, heat or

cold.
 In general, the use of neurolytic techniques has diminished in the last
two decades. There are many reasons for this, including the
improved use of analgesic drugs, the recognition that the effect of
neuro ablative procedures is often transient, the development of
neurostimulatory techniques and appreciation of the cognitive and
behavioural elements of pain.
 The clinical indications for neurolytic techniques are limited to
patients with cancer pain and a few selected non-cancer
conditions. Careful thought with regard to the potential benefits
and risks of the procedure, appropriate patient selection and fully
informed consent is essential before performing a neurolytic
procedure.
 STIMULATION-INDUCED ANALGESIA
 Transcutaneous electrical nerve stimulation, spinal cord stimulation,
deep brain stimulation and acupuncture may produce stimulation-
induced analgesia.
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