BIOLOGICAL

Pain is a primary indicator of tissue pathology. From a biological perspective, pain can be divided into two pain types, based on underlying mechanisms (Box 38.1). Nociceptive pain is pain arising from pathology in somatic and visceral structures, such as bone fractures, appendicitis and renal calculi. Neuropathic pain is pain arising from pathology in neural structures, including the peripheral nervous system (e.g. diabetic neuropathic pain and postherpetic neuralgia) and the central nervous system (e.g. spinal cord injury pain and central post-stroke pain). Pain is initiated by damage or potential damage to somatic, visceral or neural tissues. However, a number of secondary changes including sensitisation at the periphery (peripheral sensitisation) and in the central nervous system (central sensitisation) are associated with trauma and the transmission of pain signals.² These secondary processes further amplify the pain experience. This means that the treatment of pain often needs to address these secondary changes as well as the underlying cause or generator of the pain.

PSYCHOLOGICAL

Psychological processes are also extremely important in the experience of pain.³ Although many texts refer to psychogenic pain, pain caused by psychological factors is rare and the term may be unhelpful. On the other hand, psychological factors invariably contribute to pain and are a large determinant of the intensity and quality of the pain experience as well as the behaviours that arise as a result of nociceptive and neuropathic stimuli. Mood dysfunction is also a very common consequence of pain. Therefore psychological factors need to be considered and assessed in any person who presents with pain.

Psychological factors fall into two main categories. Alterations in mood, such as depression, anger, fear and anxiety, may contribute to the pain problem. Our emotional state is strongly linked to activation of descending pathways from the brain to the spinal cord that control the level of amplification of pain signals coming in from the periphery. Both depression and stress-induced anxiety result in increased levels of neurochemicals that result in amplification of incoming pain signals. This results in an increase in the levels of pain that we experience. Therefore, reducing anxiety by providing reassurance and support as well as appropriate management of depression helps to relieve pain by decreasing the level of amplification of pain signals. Unhelpful cognitions such as expectation of pain, catastrophising and fear avoidance may also contribute to and exacerbate both pain and pain-related disability.

Brain imaging studies demonstrate that the perception of pain is not localised to any one brain structure or region, but involves the interaction of many regions that register and modify pain signals, including those involved with attention, mood, emotion, fear and cognition. It is therefore extremely difficult to separate the physical aspect of the pain experience from the suffering that accompanies it. ‘Pain’ can also be experienced vicariously. Empathy, or experiencing another’s pain, has been shown to produce changes in brain activity in the observer that are similar to those in the loved one who is actually experiencing the physical pain—apart from the localisation of any pain inputs.⁴

Concluding that mind and emotion affect the experience of pain does not imply that the pain is ‘imagined’ but that the relationship between pain perception and the extent of physical tissue damage is very variable. There is strong evidence indicating that the central nervous system is sensitised in many chronic pain states, and it is hypothesised that this sensitisation may be maintained by ‘sustained attention and arousal’.^5,6 This means that a person with chronic pain can have accentuated pain in the presence of hypervigilance, preoccupation and neuronal hyperactivity, and may go some way to explaining why emotional state has such a major effect on symptomatology for people with chronic pain syndromes. These physiological and psychological changes provide a link between mind and body and a connection between mood, cognitions and the sensation of pain. From a therapeutic perspective, helping to diminish hypervigilance and reactivity to the experience of pain may explain on a clinical and neurological level the better outcomes of people with chronic pain syndromes who include psychological strategies such as stress management or mindfulness as part of their therapeutic approach. Other reasons why the relaxation response or improving emotional state and mental health may help with chronic pain include reduction in muscle tension, the anti-inflammatory effect of stress reduction, improved responsiveness to endorphins and effects on gamma aminobutyric acid (GABA).^7,8

SPIRITUAL

There is very little information regarding the contribution of spiritual factors to the experience of pain. Even the concept of spirituality is poorly defined. Spirituality is not limited to the religious dimension, and many see spirituality in broad terms involving meaning, purpose and connectedness with no religious connotations. Most people would identify certain activities and relationships that give them a sense of purpose and that enrich and energise them at a deep level. From this perspective, pain can have a significant impact on a person through the disruption of these important and meaningful activities and relationships. This in turn can contribute to the physical experience of pain and add further to depression and loss of hope. However, the relationship between pain and spirituality is not all negative. For many people, the experience of pain can be an opportunity for growth as they re-evaluate their priorities, relationships and direction and find new sources of strength, meaning and hope.

ENVIRONMENTAL INFLUENCES

Pain does not occur in isolation but instead within a context that has a direct bearing on the experience of pain and the person’s response to pain. Environmental influences can be divided into three broad categories: physical, social and spiritual (Fig 38.2). Physical factors that arise from a person’s working or living situation and recreational activities may directly influence or cause pain. For example, for someone in a sedentary occupation with chronic pain, seating posture may have a large bearing on the presence of pain. Social factors such as relationships with family, friends, colleagues, employer or supervisor and cultural background can also strongly influence a person’s experience of pain and their pain behaviour. For example, the way a spouse or partner responds to a person’s pain is a major determinant of the way in which a person with pain will behave. Spiritual factors refer to non-physical, non-personal factors that may influence a person’s experience of pain. From a religious perspective, it is known that a person’s view of God affects their pain. For example, those who view God as punishing or cruel have worse pain outcomes than those who see God as forgiving.⁹ Many people without any religious affiliation also attribute improvement in their pain to an inherent, ‘supernatural’ ability of certain objects, people or a ‘higher power’. Whether these improvements are real or imagined and whether they are simply due to the physical or psychological properties of the intervention is a matter of ongoing debate and study. Nevertheless, it is difficult to consider a person’s pain from a holistic perspective without recognising and assessing the possible contribution of these factors to their pain experience.

FIGURE 38.2 Interaction between the person and their environment

AIMS OF ASSESSMENT

One aim of pain assessment is first to identify the contribution of biological factors to pain, whether nociceptive or neuropathic. The distinction between nociceptive and neuropathic pain is made because the underlying mechanisms giving rise to pain appear to be different, with different pain characteristics and response to treatment (Table 38.1). Nociceptive pain is often dull or aching and, in the case of musculoskeletal pain, related to activity or position. Although not diagnostic, neuropathic pain is suggested by descriptors such as burning, electric and shock-like with pain present in a region of sensory disturbance. Neuropathic pain often occurs in the absence of stimulation, and minor stimulation such as light touch can lead to exaggerated pain (allodynia).

TABLE 38.1 Distinguishing nociceptive from neuropathic pain

* Dysaesthesia: unpleasant abnormal sensations, e.g. ants crawling under the skin.

It is also important to assess the contribution of psychological, spiritual and environmental factors. Assessment of psychological function includes determining disturbances in mood such as anxiety or depression. It also includes assessing the patient’s cognitions, such as their beliefs regarding the cause of their pain, their expectations and preferences for pain management, fear avoidance behaviours, lack of belief in their ability to function normally (self-efficacy), the level of relief they need in order to return to previous activities and the strategies they use to cope with their pain. Assessment of spiritual factors may be as simple as finding out what activities and relationships are important to the person and how these have been affected by the pain. This may help understand what gives them strength, purpose and meaning in their life. Further enquiries about a person’s beliefs and spiritual practices and how they influence or have been influenced by their experience of pain may also be helpful. Obtaining an environmental history focuses on elucidating any factors in their environment that may be contributing to the pain problem. It includes determining the social context of the patient, such as significant relationships, work, hobbies and activities and how these may be acting to reinforce the pain or hinder recovery.

FIGURE 38.3 Pain intensity scales

As well as the contributors to pain, assessment aims to identify the functional consequences of pain. This will almost certainly involve the whole person and include physical, psychological and spiritual consequences. For example, acute pain is often associated with physical changes such as an increase in heart rate and blood pressure, pupil dilation and mood changes such as anxiety. Cancer pain may be associated with loss of appetite, anxiety about the diagnosis, and fears and re-evaluation of hopes for the future. A person with chronic non-cancer pain may have postural changes associated with an abnormal gait, sleep disturbance, depression, fear avoidance of activities, interference with social and recreational activities, and loss of identity and meaning in their relationships and work. Although these changes may not be directly contributing to pain, they are important components of the pain problem that need to be addressed. While some may resolve or improve if the pain can be relieved, others may be persistent or severe and require separate attention.

PAIN HISTORY

Taking a patient history is usually the first step towards identifying the main contributors and consequences associated with a person’s pain problem. A history provides information that allows some direction as to whether the pain is primarily somatic, visceral or neuropathic, as well as identifying contributing psychosocial factors. For example, lumbar spinal pain precipitated by a lifting incident, that is related to movement, eased by rest, with no radiation to the legs, no numbness or paraesthesiae and a positive response to simple analgesics, including anti-inflammatory drugs, all suggest a primarily somatic nociceptive pain. In addition, sleep disturbance, loss of appetite and loss of enjoyment of activities suggest an accompanying mood disturbance.

A clear history will then provide the basis for further examination and investigations that further refine these preliminary observations. In addition, the history will provide clues regarding other aspects of the person’s presentation. The patient’s manner, tone, emphasis of certain facts, expressions and language will all help to convey important aspects of their expectations, understanding of their problem and emotional state. Although there are many variations on taking pain history, the basic elements consist of:

EXAMINATION

As mentioned above, biological pain generators can be broadly divided into nociceptive or neuropathic. Therefore the physical examination can be broadly divided along these same lines into musculoskeletal (or visceral) and neurological (Box 38.3). Other body systems (e.g. cardiovascular, respiratory and gastrointestinal) may also require examination, depending on the individual’s presentation. For example, a poor cardiovascular history in a person with low back pain should alert the clinician to the possibility of an underlying vascular cause. This would then warrant careful examination of the vascular system and, potentially, further investigation.

The aim of a physical examination is to identify, where possible, the nature and location of the pathology that may be giving rise to the pain. In addition, any secondary physical consequences or features of the pain, such as muscle deconditioning, allodynia or hyperalgesia, may be a focus of treatment in themselves.

INVESTIGATIONS

A wide range of investigations may be indicated to complete an assessment of a patient presenting with persistent pain (Box 38.5). Unfortunately, while most investigations can demonstrate sinister pathology (e.g. fracture, infection, cancer and progressive neurological problems), they are less helpful in identifying the specific mechanisms that may be contributing to persistent pain. For example, in patients with spinal pain, it has been demonstrated that there is a poor correlation between pain report and the presence of pathology on anatomical imaging, even using sophisticated techniques such as magnetic resonance (MR) imaging of the spine.^10,11 In patients with sciatica, imaging is recommended in the acute stage only if there are ‘red flags’ such as possible infection or malignancy rather than disc herniation, or in the person with severe symptoms who does not respond to 6–8 weeks of conservative management.¹²

BOX 38.5 Investigations

Imaging

The diagnosis of pain relies heavily on imaging techniques. These include:

• X-rays (although of limited value in the diagnosis of back pain and sciatica)

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