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The definition of chronic pain currently rests primarily upon its duration: pain lasting for less than three months is considered acute, and pain lasting for more than three months, chronic. However, medical professionals often use greater flexibility in their diagnosis of pain as chronic, with some categorizing chronic pain as ‘any pain that has lasted for longer than it should have’ (Allan, personal communication). This ad hoc definition allows for context specific judgements to be made which take into account the nature, location and cause of the pain and the typical time-line that that sort of pain usually displays.

The distinction between acute and chronic pain has sometimes been understood as reflecting qualitatively different types o f pain and it has certainly been used as a basis for offering different types o f intervention. Typically, acute pain has been viewed as pain which is most appropriately treated within a biomedical framework (e.g. with medication and bed-rest) whilst chronic pain has been viewed as a more complex problem than acute pain and more suited to psychological intervention. Karoly (1985), for example, notes that:

“The complex, interactive processes that modulate pain appear less likely to be invoked in discussions o f acute pain (which is, therefore, left to be dealt with in more or less traditional, “medicalistic” ways)” (p. 467).

In the case of chronic pain there has often been a similar omission o f understanding psychological factors as central to the experience o f pain; rather psychological factors have been hypothesized as producing ‘overlay’ on top o f the pain. For example, Fordyce (1976) conceptualises chronic pain within a behavioural

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framework whereby much o f the disability associated with the pain (e.g. reduced activity levels, loss o f work) is viewed as the result of learned pain behaviours which have been reinforced over time.

Qualitative differences between acute pain and chronic pain sufferers have been explored, for example, by Keefe, Block and Williams (1980). They examined chronic pain sufferers following their first two months o f treatment for pain through to two years later. They characterized the acute phase (0-2 months) as being one where patients were typically anxious, showing signs o f heightened autonomic arousal, temporary decreases in activity levels and a reliance on medication and medical treatment. However, as time passed (2-6 months), whilst pain sufferers’ autonomic arousal levels were still high, they were beginning to realize that their pain could not be controlled by medication. At this point some attempted to return to work. In what they described as the chronic phase (6- 24 months), Keefe et a l (1980) found that autonomic arousal was typically reduced, and instead of being anxious, pain sufferers often became depressed. At this point, activities had often decreased permanently, including work loss, and the pain sufferers were characterized as preoccupied with bodily complaints. Hence Keefe et a l proposed that acute pain is characterized as associated with anxiety and active treatment seeking, whereas chronic pain is characterized as associated with depression and inactivity.

The transition from acute to chronic pain

Given the lack o f understanding about why pain continues beyond the recognized healing time o f three months, some research has begun to focus more on the development o f chronic pain from an acute pain state.

The proportion o f acute pain sufferers who continue to experience pain beyond the recognized healing time o f 3 months has been reported as being between 20 and 40% (Radanov, Di Stefano, Schnidrig and Sturzenegger, 1993; Philips and Grant,

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o f early interventions to prevent developing chronicity is clearly o f clinical and economic value. Gervais, Dupuis, Veronneau and Bergeron (1991), for example, estimated that identification o f and intervention for patients at risk from continued work disability following one episode of compensated low back pain could save up to 396 Canadian dollars per patient per year.

fri a longitudinal study. Philips, Grant and Berkowitz (1991) identified several measures at baseline (i.e. taken an average o f 15 days after an initial attack o f pain), which predicted the presence o f pain at 3 months. These included pain located in the upper back, higher baseline levels of pain, more negative cognitive reactions to pain and higher anxiety. However, the only baseline variable predicting the presence of pain at 6 months was pain intensity at baseline.

Whilst considerable changes may take place over the initial three month period following pain onset, Philips and Grant (1991) conclude that the pattern o f change over longer periods, e.g. six months, reflected the persistence o f an acute pain state that fails to extinguish, rather than the growth and development o f a chronic pain state (as hypothesized by Fordyce and presented by Keefe et al., 1980). Indeed Philips and Grant argued that many of the changes observed over the first three months represented adaption to the pain. For example, they found that the highest degree of discordance between measures of perceived disability and pain intensity were recorded at baseline, with the lowest degree o f discordance occurring at 3 months, reflecting positive adjustment to the pain over this time with relative stability in measures taken between 3 and 6 months.

This result could be interpreted as suggesting that the development o f chronicity critically depends on the pain sufferer’s initial response to the pain, rather than the development of maladaptive coping strategies occurring over subsequent weeks. An equally viable interpretation could be that maladaptive changes take longer to develop

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and emerge after 6 months, taking a major role in the chronic pain disorder once it has become established rather than playing a role in its development per se.

Hellsing, Linton and Kalvemark (1994) conducted a community based investigation into people reporting acute back and/or neck pain and conducted a prospective study to examine which factors predicted development o f chronicity. They found that there was no difference between those who went on to develop chronic pain and those who did not, in terms of age, amount o f pain or functional impairment. However they did demonstrate that the risk o f developing chronic pain was fives times higher:

“for those patients whose pain was provoked by trunk movements in several directions at the first clinical examination” (p. 116).

which suggests that the type and extent of initial damage might be crucial.

Whilst there are likely to be factors involved in long-term pain which are irrelevant for acute pain, particularly in terms of life-impact, it is not necessarily the case that chronic pain is in need of greater explanation than acute pain. It seems that the reasons why pain continues beyond the recognized healing time o f three months is as much a mystery as why pain disappears before three months. Hence a deeper understanding of pains o f all types and duration could be valuable in understanding chronic pain.