The Biopsychosocial Model in Pain Cases

The definition of pain, as ‘an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage’ (1) recognises that the phenomenon is more than just a physical event. Indeed, when we talk of someone ‘suffering’ from pain, we are predominately referring to the emotional experience (2). Pain is the most common reason for a visit to the doctor’s surgery (3) and it is estimated that, in the developed world, around 40% of adults are suffering from chronic pain at any one time (4). Pain is a complex and variable condition, which often has no obvious cause. These factors make it more difficult to treat than many other medical conditions (3).

Historically, pain has always been viewed as a biomedical issue requiring a physical treatment such as medication or surgery (2,4). This model explains illness as a somatic process within the body, with a focus on biochemical and neurophysiological abnormalities, and assumes that psychological and social factors are largely irrelevant in disease causation. However, as psychosomatic medicine became more established, the important link between biological and psychosocial factors was highlighted and the role of factors such as personality, attitudes and beliefs, and resilience gained greater prominence (2). While it is commonly believed that pain equals harm, in chronic pain this is often not the case – it is in fact more closely linked with nerve sensitivity than tissue damage. However, beliefs about pain can shape behaviour: negative beliefs can result in depression and increased disability, leading to more pain. Often, this becomes a vicious cycle (5).

The biopsychosocial model takes a ‘whole person’ approach to disease and recognises that the mind and body act together. Thus, illness and pain have biological, psychological and social components that influence each other (2,4,6), although the direction of these relationships can vary (6). Thus, individual differences in these interactions may account for the unique pattern of symptoms experienced by each patient (2). In terms of pain causation, this interdependency between environmental and genetic factors provokes long-term changes in biological and psychological regulatory systems. The physiological effects of psychological and physical stresses may play an important part in this process. Demands on the stress response system, particularly where these become chronic, may moderate central pain processing and influence signals from the brainstem (7).

Within the broader definition of the biopsychosocial model, a number of more specific models have been developed in order to explain how various factors may influence pain-related outcomes. Perhaps the best-known of these is the Fear Avoidance Model (FAM). This model suggests that fear of pain leads to other negative cognitive, emotional and behavioural processes, which are interacting and cyclical, ultimately resulting in pain-related disability. The cycle can be modulated by behavioural responses that can be classified as either ‘confrontation’ or ‘avoidance’. Confrontation strategies lead to reduction of the fear over time, while avoidance behaviours result in maintenance of, or an increase in, fear, which itself leads to more disability. Clinical studies have shown that fear avoidance behaviours are associated with higher levels of pain and disability and poorer treatment outcomes, including a reduced frequency of returning to work. However, while these associations may be strong, there is little evidence of a specific temporal pathway (4).

The Avoidance Endurance Model (AEM) is similar to the FAM, but differs in that it realises the importance of specific behaviours in pain causation and maintenance. The model suggests that in patients experiencing chronic pain, some will become fearful and avoid activity, while others will show an ‘endurance response’, in which they remain active. The precise type of endurance response is determined by emotional and cognitive processes. Patients who are anxious will tend to show a maladaptive endurance response, while those who are more positive and perceive pain as less of a threat will have a more adaptive response. Thus, the interconnection between psychosocial factors and behaviour is highlighted in the AEM (4).

These models seek to show how psychosocial factors shape individual variability in pain-related outcomes, and particularly how specific characteristics can increase or reduce the risk of an acute pain condition becoming chronic. These characteristics, which can be defined as ‘general’ or ‘pain-specific’, are not restricted to any one condition but have been observed in many pain-related illnesses. General psychosocial factors include conditions such as depression, anxiety and other indices of emotional distress, along with previous trauma and post-traumatic stress disorder (PTSD). There is overwhelming evidence that all of these factors contribute significantly to long-term outcomes of persistent pain, such as physical disability, healthcare costs and mortality. Of all these factors, PTSD arguably shows the strongest association with chronic pain, and it also plays a role in the transition from acute to chronic pain. However, it is not clear whether the association between trauma and chronic pain is direct or is driven by emotional, cognitive and behavioural responses to the traumatic event (4).

Of the pain-specific psychosocial factors, catastrophising is perhaps the most important. This term describes a constellation of negative cognitive and emotional processes such as helplessness, pessimism, obsessive thoughts about pain-related symptoms and magnification of reported pain. As well as correlating with general psychosocial factors such as depression and anxiety, catastrophising is specifically associated with pain-related outcomes and is a known risk factor for the development of chronic pain. Conversely, self-efficacy, which affects an individual’s ability to cope with challenging situations, is, not surprisingly, a protective factor (4,6). Individuals with high self-efficacy are more resilient and report lower pain intensity, as well as lower levels of disability. This resilience may help to explain how some patients are able to live with chronic pain without experiencing disability (4).

Until recently, treatment for pain focussed chiefly on nociceptive pain and consisted almost entirely of pharmacological treatments or surgery. Thus, the psychological aspects of pain were more or less ignored (3). However, the adoption of the biopsychosocial model in pain medicine has led to the development of interdisciplinary management programmes for chronic pain (8,9). An interdisciplinary approach integrates several disciplines into a cohesive team that is responsible for all aspects of a patient’s care and it is usual for the entire treatment team to meet with the patient at the same time, thus providing consistent advice. This differs from a multidisciplinary approach, where each discipline treats the patient separately from their own perspective (2). The interdisciplinary approach to treatment has proved to be more effective, both in terms of cost and therapeutic improvements (2,8). Treatments aimed at prevention and early intervention may also help to reduce the number of patients who require long-term opioid use (2). Programmes such as cognitive behavioural therapy have been successfully used to reduce factors such as catastrophising, and the effects may last for a considerable length of time (4).

Although the biopsychosocial model of pain is now widely supported, it has attracted some criticism. One issue is that the specific pathways by which the various elements in the model interact to cause illness, and the direction of these effects, have yet to be clearly identified (4,6). Furthermore, many of the explanations invoked to account for variation between patients are so multifactorial that they cannot be proven by research. It has also been suggested that the biopsychosocial model may place undue weight on psychosocial factors, especially in conditions where clear anatomic pathology is lacking (4). It is actually quite likely that the importance of any one factor may vary over time. Physical factors are likely to be more important in the early stages of a disease, while psychological factors may become more influential as time, and the patient’s condition, progresses, due to the perceived loss of quality of life (6). The model has also been criticised for being too restrictive in that it fails to capture important influences on quality of life, such as religious affiliation and spirituality, pain behaviours and social response behaviours. It is also important not to confuse psychological symptoms and processes with manifest psychiatric illness (4).

Pain is a complex and variable condition and requires an understanding of the multiple factors that combine to influence the trajectory of a patient’s illness (4). The biopsychosocial model is generally accepted as the most heuristic approach to pain, in that it allows patients to understand their pain and how their beliefs and attitudes may shape their experience of it (2,10). It takes account of the fact that predisposition to illness or injury, psychological and social factors, and physiology are all important in the development and treatment of chronic pain (2). Although the biopsychosocial model does have some limitations, it has helped to improve understanding of individual variation in the experience of pain. It has also led to the development of effective treatments for this highly challenging condition.

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References

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