CHRONIC PAIN

EPIDEMIOLOGY:

A systematic literature review of chronic pain found that the prevalence of chronic pain varied studies in various countries from 10.1% to 55.2% of the population, affected women at a higher rate than men, and that chronic pain consumes a large amount of healthcare resources around the globe.⁽¹⁾

A large-scale telephone survey of 15 European countries and Israel, 19% of respondents over 18 years of age had suffered pain for more than 6 months, including the last month, and more than twice in the last week, with pain intensity of 5 or more for the last episode, on a scale of 1 (no pain) to 10 (worst imaginable). In an internet study, the prevalence of chronic pain in the United States was calculated to be 30.7% of the population: 34.3% for women and 26.7% for men.⁽⁶⁾

In less developed countries in South East Asia the prevalence rates varied from 5.2% in India, 8.8% in Pakistan to 43.2% in Thailand.⁽⁷⁾

PATHOPHYSIOLOGY:

Under persistent activation nociceptive transmission to the dorsal horn may induce a pain wind-up phenomenon. This induces pathological changes that lower the threshold for pain signals to be transmitted. In addition it may generate non-nociceptive nerve fibres to respond to pain signals. Non-nociceptive nerve fibers may also be able to generate and transmit pain signals. The type of nerve fibers that are believed to propagate the pain signals are the C-fibers, since they have a slow conductivity and give rise to a painful sensation that persists over a long time.⁽⁸⁾ In chronic pain this process is difficult to reverse or eradicate once established.⁽⁹⁾ In some cases, chronic pain can be caused by genetic factors which interfere with neuronal differentiation, leading to a permanent reduction in the threshold for pain.⁽¹⁰⁾

Chronic pain of different aetiologies has been characterized as a disease affecting brain structure and function. Magnetic resonance imaging studies have shown abnormal anatomical⁽¹¹⁾ and functional connectivity, even during rest^(12,13) involving areas related to the processing of pain. Also, persistent pain has been shown to cause grey matter loss, reversible once the pain has resolved.^(14,15)

These structural changes can be explained by the phenomenon known as neuroplasticity. In the case of chronic pain, the somatotopic representation of the body is inappropriately reorganized following peripheral and central sensitization. This maladaptive change results in the experience of allodynia or hyperalgesia. Brain activity in individuals with chronic pain, measured via electroencephalogram (EEG), has been demonstrated to be altered, suggesting pain-induced neuroplastic changes. More specifically, the relative beta activity (compared to the rest of the brain) is increased, the relative alpha activity is decreased, and the theta activity both absolutely and relatively is diminished.⁽¹⁶⁾

NATURAL HISTORY:

Chronic pain has been defined as pain which lasts beyond the ordinary duration of time that an insult or injury to the body needs to heal. An argument has been made that the term "persistent pain" should be used in lieu of "chronic pain".

Following terms are commonly used descriptors of altered sensation:

• Hyperalgesia — Increased response to a stimulus that normally is painful.
• Hypoalgesia — Diminished response to a normally painful stimulus.
• Analgesia— Absence of pain in response to stimulation that normally is painful.
• Hyperesthesia— Increased sensitivity to stimulation, excluding the special senses.
• Hypesthesia— Diminished sensitivity to stimulation, excluding the special senses.
• Dysesthesia— An unpleasant abnormal sensation, whether spontaneous or evoked.
• Paresthesia— An abnormal sensation, whether spontaneous or evoked.
• Allodynia — Pain resulting from a stimulus (such as light touch) that does not normally elicit pain

SIGNS AND SYMPTOMS:

The symptoms of chronic pain include:⁽¹⁷⁾

• Mild to severe pain that does not go away
• Pain that may be described as shooting, burning, aching, or electrical
• Feeling of discomfort, soreness, tightness, or stiffness

Pain is not a symptom that exists alone. Other problems associated with pain can include:

• Fatigue
• Sleeplessness
• Withdrawal from activity and increased need to rest
• Weakened immune system
• Changes in mood including hopelessness, fear,depression, irritability, anxiety, and stress
• Disability

DIAGNOSTIC TESTS:

Pain is a subjective complaint and cannot be assessed with laboratory studies. However, appropriate laboratory, imaging, and other testing can be helpful to evaluate or follow certain painful conditions. It should be borne in mind, however, that finding an abnormality in a diagnostic test does not confirm that this is the source of the patient’s pain syndrome.

BLOOD TESTS: “Routine” blood studies are not indicated, but directed testing should be ordered when specific causes of pain (i.e. rheumatologic, infectious, or oncologic) are suggested by the patient's history or physical examination. Serologic markers of inflammation such as erythrocyte sedimentation rate and C-reactive protein should be normal in degenerative or neuropathic causes of pain but may be elevated in patients with polymyalgia rheumatica, rheumatoid arthritis, or infectious processes (e.g. septic discitis)

IMAGING: It is likely that patients with chronic pain complaints will already have had diagnostic imaging studies from previous evaluations, and these should be obtained and reviewed if possible, to avoid unnecessary radiation exposure and expense.

Indications for imaging and other studies will vary depending on the location of the patient's pain.

OTHER TESTING: Neurophysiologic testing, principally nerve conduction studies (NCV) and electromyography (EMG), are frequently employed in suspected disorders of the peripheral nervous system. The usual techniques, with surface electrodes for nerve stimulation, measure activity of the largest and fastest conducting sensory and motor myelinated nerve fibers.

Unfortunately, NCV and EMG studies may be normal in patients with polyneuropathies or focal nerve lesions with only small-fiber involvement. Additionally, pain specialists may perform interventional testing of nerves or joints via a double-comparative local anesthetic blockade (e.g. with one block using a longer acting anesthetic).

SPECIAL CONSIDERATIONS IN SPECIFIC POPULATIONS:

PSYCHIATRIC COMORBIDITY: Patients with longstanding or complex pain problems should be treated with a multidisciplinary approach that includes an evaluation and close collaboration by a mental health professional who can diagnose and treat the psychologic aspects of the dysfunction.

Chronic pain can take an emotional toll, affecting relationships with loved ones, friends, and potentially employers. Patients commonly describe a lack of pleasure and an absence of control in their lives.

A number of instruments or psychological tests are widely employed to screen the psychological profiles of chronic pain patients. Two that are in common use are the Beck Depression Inventory and the Minnesota Multiphasic Personality Inventory II (MMPI-2). The former is a brief, 21-item, self-reporting questionnaire that assesses the degree to which depressive symptomatology is present. The latter is an extensive true/false questionnaire consisting of more than 500 items factored across 10 clinical scales, as well as a variety of validity, secondary, and experimental scales. The MMPI-2 has been used extensively to verify clinical impressions about the psychological aspects of a patient's chronic pain and to predict responses to medical and surgical pain treatments.

OLDER ADULTS: Successful pain management in the older adult, as with younger individuals, is predicated on a comprehensive pain assessment. Specific goals include determining the type and cause of pain; identifying exacerbating co-morbidities; reviewing beliefs, attitudes, and expectations regarding pain; and gathering information that would assist and impact an individualized treatment plan.

Self-report of pain is the most reliable source for the cognitively intact and communicative older adult. However, older patients may have more difficulty in communicating their pain, and are often undertreated for pain. Deficits in vision, hearing and cognition are common in this population and need to be identified prior to beginning the interview.

For a variety of reasons, older adults may be more hesitant than younger individuals to report pain. Older adults also may use different descriptive terms for their pain (aching, soreness, hurting, discomfort).

MEDICATION HISTORY: A careful medication history must include all current and past medications, doses, side effects, and response. Many older individuals living in the community cannot accurately provide this information. It is helpful to ask that they bring in all current medications, as well as to obtain corroborative information from other treating clinicians and from relatives and to obtain the name and phone number of the patient's current pharmacy.

Patients should be specifically questioned about use of herbal and dietary supplements, as well as over the counter medications, in addition to prescription medications. Additionally, patients should be asked about alcohol use, with specific inquiry regarding type, frequency and amount. Tobacco products and illicit drug use are important elements of inquiry as well.

FUNCTIONAL ASSESSMENT: Cognition is grossly assessed during the process of the health interview. More detailed assessment may be indicated for patients who seem to have cognitive impairment.

PSYCHOSOCIAL ASSESSMENT: Mood, social support systems, recreational involvement, and financial resources are important to the psychosocial assessment. These factors influence how the patient experiences the pain and how the patients may respond to various treatments.

NONVERBAL OR COGNITIVELY IMPAIRED ADULTS: Five key principles to guide pain assessment in nonverbal populations have been identified by the American Society for Pain Management Nursing (ASPMN). These are:

• Obtain a self-report of pain, if at all possible
• Investigate for possible pathologies that could produce pain
• Observe for behaviors that may indicate pain
• Solicit a surrogate report from an observer or caregiver
• Consider the use of an analgesic trial to evaluate whether pain management results in a reduction in the behavioral indicators thought to be related to pain

A variety of behavioral tools have been developed for pain assessment in nonverbal older adults, but none has been found to have sufficient reliability and validity to support broad adoption in clinical practice.

TREATMENT OPTIONS:
PHARMACOLOGICAL THERAPY:
There are several categories of medications that are used for the treatment of chronic pain. The most commonly used medications can be divided into the following broad categories:

ANALGESICS:

Analgesics are commonly used for many pain syndromes. Pain control is essential to quality patient care. Analgesics ensure patient comfort, promote pulmonary toilet, and have sedating properties, which are beneficial for patients who have sustained traumatic injuries.

• Oxycodone: Long-acting opioids may be used in patients with CPS. Start with a small dose and, if appropriate, gradually increase it.
• Fentanyl: It is the drug of choice for conscious-sedation analgesia. Fentanyl is ideal for analgesic action of short duration during anesthesia and during the immediate postoperative period. It is an excellent choice for pain management and sedation of short duration (30-60min). Fentanyl is easy to titrate and is easily and quickly reversed by naloxone. When the transdermal dosage form is used, most patients achieve pain control with 72-hour dosing intervals; however, some patients require dosing intervals of 48 hours.
• Acetaminophen: Acetaminophen is the drug of choice for the treatment of pain in patients with documented hypersensitivity to aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs), with upper GI disease, who are pregnant, or who are taking oral anticoagulants.

NONSTEROIDAL ANTI-INFLAMMATORY DRUGS:
NSAIDs have analgesic, anti-inflammatory, and antipyretic activities. Their mechanism of action is not known, but they may inhibit cyclo-oxygenase activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell membrane functions.

• Ibuprofen: Ibuprofen is the drug of choice for patients with mild to moderate pain.
• Naproxen sodium:
• Diclofenac:
• Indomethacin: Indomethacin is thought to be the most effective NSAID for the treatment of ankylosing spondylitis, although no scientific evidence supports this claim.
• Ketoprofen: Small dosages are indicated initially in small patients, elderly patients, and patients with renal or liver disease. Doses higher than 75 mg do not increase the therapeutic effects. Administer high doses with caution, and closely observe the patient's response.
• Etoricoxib: It is also used for relief of mild to moderate pain

They are used for relief of mild to moderate pain; they inhibits inflammatory reactions and pain by decreasing the activity of COX, which results in a decrease of prostaglandin synthesis.

ANTIDEPRESSSANTS:

Some antidepressants may be very helpful in controlling pain; specifically the tricyclic antidepressants. The pain relieving properties of these medications are such that they can relieve pain in doses that are lower than the doses needed to treat depression.

• Amitriptyline: Amitriptyline is an analgesic for certain chronic and neuropathic pain.
• Nortriptyline: Nortriptyline has demonstrated effectiveness in the treatment of chronic pain by increasing synaptic concentration of serotonin and/or norepinephrine in the CNS. Pharmacodynamic effects such as the desensitization of adenyl cyclase and down-regulation of beta-adrenergic receptors and serotonin receptors also appear to play a role in its a
• Duloxetine: Duloxetine is indicated for diabetic peripheral neuropathic pain. It is a potent inhibitor of neuronal serotonin and norepinephrine reuptake.
• Venlafaxine: Venlafaxine inhibits neuronal serotonin and norepinephrine reuptake. In addition, it causes beta-receptor down-regulation. Venlafaxine may decrease neuropathic pain and help with sleep and other mood disorders (depression or depressive symptoms).
• Fluoxetine: Fluoxetine is an atypical non ̶ tricyclic antidepressant (non-TCA) with potent specific 5HT-uptake inhibition and fewer anticholinergic and cardiovascular adverse effects than TCAs. Consider this drug as an alternative to TCAs.
• Sertraline: Sertraline is an atypical non-TCA with potent specific 5HT-uptake inhibition and fewer anticholinergic and cardiovascular adverse effects than TCAs. Consider it as an alternative to TCAs.
• Paroxetine: Paroxetine is an atypical non-TCA with potent specific 5HT-uptake inhibition and fewer anticholinergic and cardiovascular adverse effects than TCAs. Consider it as an alternative to TCAs.

ANTICONVULSANTS (ANTI-SEIZURE) MEDICATIONS:

These medications can be very helpful for some kinds of nerve type pain (such as burning, shooting pain). Some of them may have the side effect of drowsiness which often improves with time. Some have the side effect of weight gain.

• Gabapentin: Gabapentin has anticonvulsant properties and antineuralgic effects; however, its exact mechanism of action is unknown. It is structurally related to GABA but does not interact with GABA receptors.
• Pregabalin: Pregabalin is a structural derivative of GABA; its mechanism of action unknown. Pregabalin binds with high affinity to the alpha2-delta site (a calcium channel subunit), and in vitro, pregabalin reduces the calcium-dependent release of several neurotransmitters, possibly by modulating calcium channel function. The US Food and Drug Administration (FDA) approved it for the treatment of neuropathic pain associated with diabetic peripheral neuropathy or postherpetic neuralgia and as adjunctive therapy in partial-onset seizures.

MUSCLE RELAXANTS:

These medications are most often used in the acute setting of muscle spasm. The most common side effect seen with these medications is drowsiness.

Medications used in the treatment of spasticity include the following:

• Benzodiazepines
• Alpha2-adrenergic agonists
• Botulinum toxins (onabotulinumtoxinA, abobotulinumtoxinA, incobotulinumtoxinA, rimabotulinumtoxinB)

OPIOIDS:

When used appropriately, opioids may be very effective in controlling certain types of chronic pain. They tend to be less effective or require higher doses in nerve type pain. For pain is present all day and night, a long acting opioid is usually recommended

• METHADONE: Inhibits ascending pain pathways, diminishing the perception of and response to pain. Also a preferred agent for opioid agonist maintenance.

TOPICAL AGENTS:

Topical agents for the management of pain have several potential advantages over systemic drugs: delivery at the site of insult, lower initial rates of systemic absorption, fewer systemic effects, and patient preference. Patients often perceive topical preparations to be safer than their oral equivalents. However, significant systemic concentration can be achieved by topical application and systemic side effects are possible.

• TOPICAL AGENTS: Topical lidocaine is most appropriate for patients with well localized neuropathic pain. Although it can be used as monotherapy, it is often used as an adjunct to systemic medication.
• CAPSAICIN CREAM: Capsaicin is available as a cream (0.025 or 0.075 percent), and as a high concentration patch (8 percent). Capsaicin has been used in patients with post herpetic neuralgia, HIV neuropathy, and diabetic neuropathy.
• TOPICAL NONSTEROIDAL ANTI-INFLAMMATORY DRUGS: Topical nonsteroidal anti-inflammatory drugs, in the form of a gel, spray, or cream, provide modest relief for acute musculoskeletal pain.
• COLD THERAPY – MENTHOL: It work through a ‘counter irritant’ mechanism. This means that the menthol creates a sensation that overrides pain signals to the brain. This process is known as ‘Gate Control Theory’, where nerve impulses from one stimulus block the nerves containing pain signals to the brain.

GOALS OF THERAPY:

Goals of therapy for Chronic Pain:

• Restore function: Physical, emotional, social
• Decrease pain
• Treat underlying cause where possible
• Minimize medication use
• Correct secondary consequences of pain

GUIDELINES:

To review “Guidelines for Pain Management Programmes for adults by The British Pain Society”, please click on below link:

https://www.britishpainsociety.org/static/uploads/resources/files/pmp2013_main_FINAL_v6.pdf

To review “Guidelines of American Family physician on pain”, please click on below link:

http://www.aafp.org/afp/topicModules/viewTopicModule.htm?topicModuleId=61

To review “American pain society – clinical practice guidelines”, please click on below link:

http://americanpainsociety.org/education/guidelines/overview

To review “CDC Guideline for Prescribing Opioids for Chronic Pain, please click on below link:

http://jamanetwork.com/journals/jama/fullarticle/2503508

PRECAUTIONS:

Offer following preventions to patients:

STAY ACTIVE: Pain or the fear of pain can lead people to stop doing the things they enjoy. It’s important not to let pain take over your life.

KNOW YOUR LIMITS: Continue to be active in a way that acknowledges your physical limitations. Make a plan about how to manage your pain and don’t push yourself to do more than you can handle.

EXERCISE: Stay healthy with low-impact exercise, such as stretching, yoga, walking and swimming.

MAKE SOCIAL CONNECTIONS: Call a family member, invite a friend to lunch or make a date for coffee with a pal you haven’t seen in a while. Research shows that people with greater social support are more resilient and experience less depression and anxiety.

DISTRACT YOURSELF: When pain flares, find ways to distract your mind from it. Watch a movie, take a walk, engage in a hobby or visit a museum. Pleasant experiences can help you cope with pain.

DON’T LOSE HOPE: With the right kind of psychological treatments, many people learn to manage their pain and think of it in a different way.

FOLLOW PRESCRIPTIONS CAREFULLY: If medications are part of your treatment plan, be sure to use them as prescribed by your doctor to avoid possible dangerous side effects. In addition to helping you develop better ways to cope with and manage pain; psychologists can help you develop a routine to stay on track with your treatment.

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