A world of pain

By Steven P. Cohen

Chronic pain affects more people and costs more to treat, yet it is often easy to treat the wrong way

Pain is ubiquitous in life. Inextricably bound to consciousness, it is an experience that all living creatures with advanced nervous systems share. For our ancestors, whose lives were fraught with danger, pain conferred an evolutionary advantage, signaling the need to separate oneself from its immediate source. But evolution has failed to keep pace with biomedical and technological advances, allowing chronic pain (pain that persists beyond an acute injury or condition) to become a disease in itself.

It is difficult to overestimate chronic pain’s societal impact. According to the US Institute of Medicine, one in three people suffer from chronic pain – more than from heart disease, cancer, and diabetes combined. Pain is the leading cause of disability, especially back pain among people under 45 years of age and joint pain in older individuals. In the United States alone, chronic pain is estimated to cost more than $600 billion annually.

Pain can be classified according to a variety of factors, such as duration or location. But the most useful categorisation is based on mechanism. Nociceptive pain, which arises from damage to non-nervous tissue, occurs when, say, a person twists an ankle. An example of chronic nociceptive pain is arthritis. Neuropathic pain, by contrast, arises after a lesion or disease affects the nervous system. Nerve damage resulting from diabetes (diabetic neuropathy) and persistent pain after shingles (postherpetic neuralgia) are among the most common causes.

Chronic pain is difficult to treat; even the most effective medications provide only modest relief to a minority of patients. This can be explained partly by pain’s subjective nature, and partly by the fact that its source can be difficult to pinpoint.

Although neuroscientists are adept at studying pain, animal models fail to account for its “affective-motivational” component – that is, pain’s emotional, cognitive, and contextual features. Indeed, physiological indicators have less of an impact on a patient’s prognosis after a painful injury than psychological and social factors such as depression or poor coping skills. The problem is that subjective measures are much more difficult to study – not least because they are associated with high placebo response rates.

Unrealistic expectations exacerbate these psychological impediments to progress. In an era of instant access, people often expect immediate relief from symptoms, which is difficult to achieve when it comes to chronic pain.

For example, the best way to relieve back and neck pain is often to exercise, while treating underlying contributing factors like obesity. But few people are willing to devote the time and effort that such a therapeutic plan demands; they would prefer an injection, operation, or medication. When there is no instant fix available, they can become discouraged, hampering their recovery further.