Abstract
Chronic pain is defined as an unpleasant sensory and emotional experience persisting longer than the normal process of healing, usually longer than 3 months. About a fifth of the world’s population is believed to suffer from chronic pain. In Europe, chronic pain accounts for nearly 500 m lost working days, and it costs the European economy >€34 billion (£28 billion) every year.
Establishing a reliable diagnosis is the primary challenge in evaluating a patient with chronic pain. Common diagnoses not to miss include seronegative spondyloarthritides, endocrine abnormalities including severe vitamin D deficiency and polymyalgia rheumatica.
Once important or treatable diagnoses have been ruled out, the history can be used as a tool to establish a therapeutic plan for shared decision-making using the biopsychosocial model. Onward referral to pain clinics can be helpful for more involved patient management, but often good outcomes are achieved with the support of primary care.
Pain is defined by the International Association for the Study of Pain (IASP) as ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage’. Chronic pain has been defined as ‘pain which persists longer than the process of normal healing’ . It is now practically defined by pain that lasts longer than 3 months . There are many different chronic pain syndromes, the most common being fibromyalgia, low back pain and pain associated with degenerative conditions. In this article, we will discuss the clinical approach one should take when evaluating a patient who has chronic pain, and evaluate the evidence base around different techniques of assessment and investigation.
Story of chronic pain
‘You slip on ice and land heavily on your hand. The pain is instant. Soon, your wrist reddens and swells. It becomes painful to the touch. You rush to the A&E department of the nearest hospital and get an X-ray. Luckily, you haven’t broken anything – merely sprained your wrist. It should get better in a few days. In the meantime, your wrist hurts and you wear a wrist guard to protect it from further strain. A week later, your wrist is back to normal. You soon forget that you were ever in pain.
What if the pain doesn’t go away, though? Months pass. Your wrist gets worse. Now your whole hand hurts. Washing up and getting dressed become difficult. You start to worry and can’t sleep properly. Doctors and painkillers become a part of your life. The pain is always there, but your doctor can’t find anything wrong. No one quite understands. You feel depressed. People seem to think you’re making a big fuss. Maybe the pain is all “in your head”.
The initial injury might have been different, but this story will be familiar to many chronic pain patients. Their pain persists long after the injury is healed. Without any injury to protect, such pain serves no purpose, and becomes crippling. Chronic pain is more common than we think. About a fifth of the world’s population is believed to suffer from chronic pain. In Europe, chronic pain accounts for nearly 500 m lost working days and costs the European economy more than €34bn (£28bn) every year’.
Dr Michael Lee, Winner MRC Public Engagement series, Guardian, 29 July 2008
Epidemiology
Chronic pain and its effects on the quality of life and upon the productivity of the workforce are hugely significant. About one-fifth (20%) of all people within a population will be suffering from chronic pain, a figure validated repeatedly in large-scale validated epidemiological studies.
Breivik et al. found that 19% of 46,394 respondents had suffered pain for >6 months. In-depth interviews with 4839 respondents with chronic pain (about 300 per country) showed the following: 66% had moderate pain (numerical rating scale (NRS) = 5–7), 34% had severe pain (NRS = 8–10), 46% had constant pain and 54% had intermittent pain . Fifty-nine per cent had suffered with pain for 2–15 years, 21% had been diagnosed with depression because of their pain, 61% were less able or unable to work outside the home, 19% had lost their job and 13% had changed jobs because of their pain. Sixty per cent visited their doctor about their pain two to nine times in the last 6 months. The average number of lost days over the preceding 6 months was 8. Over the year, this would account for >3 working weeks from each individual lost due to chronic pain. Only 2% were currently treated by a pain management specialist.
In a computer-assisted telephone survey of 17,543 individuals in the Australian general adult population, which defined chronic pain as pain every day for 3 months in the 6 months before the interview, the prevalence was 18.5% . In a survey of 12,333 respondents aged over 16 years in the general population of Denmark, the overall prevalence of chronic pain lasting at least 6 months was 19% . A similar picture is seen in the USA where chronic pain has been estimated to have a prevalence of 30%, affecting 100 million people, and costing the US economy between US$550 and 626 billion each year .
Understanding chronic pain is very important for the rheumatologist. The most common reason to seek consultation with a rheumatologist is to seek a cause, and hopefully treatment and cure, for troubling pain. Patients with chronic pain are responsible for 40% of the workload of clinical rheumatologists in the UK. Being able to provide a rapid, thorough and sensitive assessment of a patient who presents with chronic pain is an essential skill for any rheumatologist.
Physiology of nociception
Nociception is the neural process of encoding and processing noxious stimuli . These are ‘stimuli’ that are damaging, or threaten damage to normal tissues, and they can be thermal, mechanical or chemical stimuli. Noxious stimuli evoke a nociceptive response at a threshold of intensity that could cause tissue damage. In general, nociception results in pain, but the transmission of pain does not require it. Furthermore, in some cases pain can be increased in relation to a nociceptive stimulus that would normally evoke less pain (hyperalgesia). Pain can even result from a stimulus that is normally non-noxious (allodynia) (IASP). The disconnection of nociception and pain is a common characteristic in many chronic pain states.
Nociceptive fibres are slowly conducting Aδ and C fibres that release glutamate and the co-localised substance P (SP) and calcitonin gene-related peptide (CGRP). The fibres carry noxious information to the dorsal horn of the spinal cord and synapse with projection neurons. The spinal gate is controlled by local spinal mechanisms (glutamate, glycine and γ-aminobutyric acid (GABA)) and descending pathways releasing serotonin and noradrenaline. The projection neurons carry the noxious information in ascending pathways including the spinothalamic tract to the lateral nuclei of the thalamus and brainstem. From here, nociceptive information passes to the cortical structures. A number of brain areas are involved in pain. A pathway from the brainstem that activates the reticular formation on its way to the thalamus and somatosensory cortex is thought to be responsible for the ‘somatic’ experience of pain, allowing localisation of a painful stimulus. Another main pathway passes through the medial nuclei of the thalamus before going into the anterior cingulate and frontal cortex, and it is thought to be responsible for the ‘emotional’ component of pain. There are also descending pathways that modulate the response of the spinal cord to noxious stimuli. Ascending pathways at the level of the medulla and midbrain activate the periaqueductal grey, raphe nucleus and the rostroventral medulla to excite descending pathways that release noradrenaline and serotonin .
Pathophysiology of chronic pain
The long-term goal in the science of chronic pain is a clear understanding of the mechanisms that underlie chronic pain syndromes. Currently, many patients with chronic pain present with symptoms that exist in the absence of tissue damage or any likely pathophysiological cause. For now, we are limited to fairly broad classification of pain . Diagram 1 outlines an approach to the clinical assessment that incorporates where each mechanism may point to an underlying diagnosis.
Mechanical pain is a nociceptive pain characterised by damage to mechanical structures such as muscles, ligaments, intervertebral discs or facet joints. Mechanical pain is aggravated by activity and relieved by rest.
Inflammatory pain is a nociceptive pain generated by inflammatory mediators (e.g., cytokines and prostaglandins) stimulating afferent neurons. Inflammatory pain is felt mainly at night, and it is associated with morning stiffness and diurnal variation. The pain tends to be localised in a region where there is also the characteristic redness, heat and swelling of an innate inflammatory response. It is seen in inflammatory arthritides, as well as in many other non-rheumatological injuries including cancers.
Peripheral neuropathic pain is caused by damage to or the dysfunction of the somatosensory system following nerve injury. It is seen in nerve root compression, traumatic nerve injuries, diabetic neuropathy and post-herpetic neuralgia, amongst others. Peripheral sensitisation occurs, resulting in characteristic hypersensitivity of neurons to pain stimuli. This can result in hyperalgesia, allodynia and spontaneous pain. Characteristic pain qualities include burning as well as numbness and paraesthesia. Central sensitisation (as below) may also contribute .
Central sensitisation is thought to be the dominant mechanism in fibromyalgia, CRPS, chronic lower back pain and other chronic pain states. It is characterised by a dysregulation of neurons and circuits in central nociceptive pathways that produces increased excitability and decreased inhibition, resulting in the uncoupling of nociception and pain perception . There does not have to be a specific nerve injury as in neuropathic pain.
Assessment of pain – history
A large body of evidence demonstrates that the doctor–patient relationship affects the outcome of the patient as measured by satisfaction, placebo–nocebo effects, litigation and health status. In an area of practice that is as subjective as ‘pain report’, good communication skills are essential .
The primary aims of the history are to acquire accurate, relevant and complete information that aids the physician in establishing a diagnosis and planning treatment. This can be summarised as follows:
- 1.
Can the history indicate a diagnosis that would explain the patient’s symptoms, symptom severity and functional limitation?
- 2.
What location and how should the examination be focussed?
- 3.
What tests should be carried out?
- 4.
What are the objectives of treatment?
- 5.
What treatments would be acceptable for the patient?
Assessment of pain – history
A large body of evidence demonstrates that the doctor–patient relationship affects the outcome of the patient as measured by satisfaction, placebo–nocebo effects, litigation and health status. In an area of practice that is as subjective as ‘pain report’, good communication skills are essential .
The primary aims of the history are to acquire accurate, relevant and complete information that aids the physician in establishing a diagnosis and planning treatment. This can be summarised as follows:
- 1.
Can the history indicate a diagnosis that would explain the patient’s symptoms, symptom severity and functional limitation?
- 2.
What location and how should the examination be focussed?
- 3.
What tests should be carried out?
- 4.
What are the objectives of treatment?
- 5.
What treatments would be acceptable for the patient?
Practice point 1: red- and yellow-flag symptoms
As in other disciplines, a ‘red-flag’ symptom is one that, if present, can indicate more serious pathology. These are very well established in low back pain ( Tables 1 and 2 ), along with the ‘yellow-flag’ symptoms, which can indicate the risk of developing chronic pain through psychogenic mechanisms . It is important to use the red flags to triage patients presenting with low back pain who require further investigations such as inflammatory markers, X-rays, magnetic resonance imaging (MRI) scans and how urgently they require such investigations. Similarly, it is helpful to assess someone’s ‘yellow’ flags to determine the level of intervention that may yield maximal cost-effectiveness for a health system . Stratified care is demonstrably more effective and economic for managing patients with low back pain if decision-making uses such simple assessment tools.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
When assessing a symptom that is multidimensional, such as pain, the challenge is to obtain information that is as clear and unambiguous as possible, given the complexity of the interconnected factors associated with pain, such as sleep, mood and function. However, there is no single agreed ‘gold standard’ in measuring the separate domains of pain, and there is a diverse range of tools available to do so .
Analyses of pain assessment have suggested that between two and seven factors best represent the core characteristics of pain and disability . We have chosen four broad categories that incorporate most of these factors:
- 1.
Self-reported pain, including the use and impact of pain-relieving medication
- 2.
Depression and anxiety as emotional factors
- 3.
Sleep
- 4.
Functional impairment including employment.
Each category lends itself to different aspects of management including evidence-based therapies. The history therefore instructs not only the diagnostic process but also the therapeutic side of the consultation.
Patients appreciate having the time to give their history, and that their symptoms are being ‘taken seriously’ . Some patients may have consulted with multiple doctors in search of diagnosis or relief and a warm and friendly manner, active listening, empathy and positive expectation will improve the quality of communication.
In patients with chronic illness, it has been shown that it is beneficial to outcomes for patients to be actively involved in their care, as a sense of agency promotes self-management and allows sensible expectations . It is important that this approach to patients begins at assessment. This includes asking open questions, encouraging patients to draw from their own experience and providing a good explanation of disease processes .
Practice point 2
The mnemonic SOCRATES can be a helpful prompt for the assessment of pain as follows:
S everity
O nset
C haracteristics
R adiation
A lleviating
T ime course
E xacerbating S ite
Severity
Pain intensity is the most commonly measured domain of pain in clinical practice . This is likely because it is a simple, quick and informative measure, and it can be taken serially to track progression. The three main scales used are verbal rating scales (VRSs), visual analogue scales (VASs) and NRSs.
Studies have shown that the VRS, VAS and NRS do not systematically disagree in assessments of chronic pain, are simple to administer and have well-established reliability . However, all these studies use factor analysis to determine if one scale performs differently to factor common to all scales. This assumes that the scales are actually measuring a true value of pain intensity, despite there being no way to determine if this is the case, given that the only way to measure pain is by self-report. It is also important that pain intensity is best used as a measure of progress, rather than a screening tool for patients with chronic pain, as it has been found to poorly identify clinically important pain .
VRSs are a list of phrases/adjectives that describe levels of pain intensity. An example would be as follows: no pain, mild pain, moderate pain, intense pain and maximum pain. Patients then choose the word or phrase that best describes their level of pain on that scale . Despite evidence demonstrating their validity, VRSs have been criticised for their lack of standardised levels between each point on the scale ; there is no way to guarantee that there is the same difference between mild–moderate and moderate–intense pain. They also require patients to be able to read and understand the phrases being presented.
VASs utilise a line, running from the extremes of ‘no pain’ to ‘maximum pain’. Patients are then asked to rate their pain by marking wherever on the line they feel best represents their pain between the two extremes . VASs may not be fully understood in a patient who has cognitive impairment, and they have been found to be the scale on which a patient is most likely to make mistakes as a result, especially with advancing age .
NRSs assess pain intensity by asking the patient to rate their pain from 0 to 10, 20 or 100. These are 11-, 21- and 101-point scales, respectively. Zero corresponds to no pain, and the highest number corresponds to the worst pain imaginable. 27 This can be presented verbally or written, although the information gained is the same. Scales with more points have the potential to be more sensitive and responsive to changes in pain; however, using a 21-point scale is generally agreed to provide sufficient specificity and discrimination . Patients also prefer it to the other scales . Overall, the NRS is slightly more responsive to changes in pain than the other scales , and it has been recommended for use by a recent systematic review .
Sensory characteristics
It is well accepted that pain can have a number of different sensory qualities; classically patients describe it as being ‘sharp’, ‘burning’, ‘dull’ among others. A recent study has found that patients with chronic pain conditions most commonly use 15 different quality descriptors as follows :
- •
Sharp
- •
Achy
- •
Throbbing
- •
Cramping
- •
Burning
- •
Dull
- •
Pressure
- •
Electrical
- •
Radiating
- •
Shooting
- •
Tingling
- •
Numb
- •
Tender
- •
Cold
- •
Sensitive
When patients with three chronic pain conditions studied (lower back pain, fibromyalgia and headache) were directly compared, the frequency that patients reported these descriptors was statistically distinct in nine out of 15 descriptors. Characteristic clusters of pain quality, although recognised as being suggestive of certain chronic pain syndromes (e.g., burning pain and neuropathic pain), cannot be used to guide diagnosis in chronic pain conditions. It can be used to indicate the type of pain that is present.
A number of scales are available for assessing the quality of pain: Pain Quality Assessment Scale, Neuropathic Pain Scale and Short-form McGill Pain Scale . Clinically, however, their usefulness in diagnosis is limited although the Neuropathic Pain Scale may direct the clinician to use anti-neuropathic agents more frequently.
Site
The location of pain need not be formally assessed in situations where there is a simple demarcated area of pain. However, in more complex situations, it can be useful to use body pain diagrams, which are representations of the anterior and posterior surfaces of the body, onto which a patient can draw where they are in pain using such questionnaires as the Brief Pain Inventory ( Fig. 1 ) They are best characterised in chronic pain syndromes such as fibromyalgia, where ‘trigger points’ have been long used in assessment (American College for Rheumatology Criteria). In these patients, the number of painful areas can be used alongside more traditional measures of pain intensity to determine the overall severity of pain . Pain diagrams might also help in patients referred to a rheumatologist, to characterise patterns of pain that correlate with rheumatic diseases . These include a polyarticular pattern having a high sensitivity for inflammatory arthritis. Location of pain can also be useful in directing treatment. Body pain diagrams have been found to be reliable in a recent systematic review .
