From Degenerative Disc Disease to Central Sensitization: A Paradigm Shift

Thomas Kuhn, a historian of science, popularized the notion of a scientific paradigm in the second half of the 20^th century and since then almost every significant change in a field of study gets characterized as a paradigm shift. So, it is a bit of a cliché to talk of the paradigm shift that is going on in the field of chronic pain management. Nonetheless, it is true. We are actually witnessing it happening.

The field of chronic pain management is undergoing a change in both how we understand the nature of chronic pain and how we subsequently treat it. While observable with any number of chronic pain conditions, this paradigmatic shift is most clear in the case of chronic back pain.

For the last twenty to thirty years, we have understood chronic back pain as a symptom of an underlying disease process of the spine called degenerative disc disease. This conceptualization has led to a common view of chronic back pain as a long-lasting orthopedic injury or condition. In the last ten years or so, a competing explanation for chronic back pain has begun to take hold. It is the notion that chronic pain is a nervous system condition, not an orthopedic condition. The condition is called “central sensitization.” It is the understanding that chronic pain results when the nervous system, including the brain, becomes stuck in a persistent state of reactivity, which leads the nervous system to become highly sensitive. The nervous system gets stuck, as it were, in a ‘hair trigger’ mode.

These competing ways of understanding the nature of chronic pain explains the occurrence of chronic back pain symptoms differently. Take, for example, symptoms of back pain that occur with normal movements, like walking, standing, leaning over, sitting down or getting up from a chair. Pain with simple movements such as these is often perplexing to the patient and their loved ones: these kinds of movements shouldn’t be painful, but they are to many patients with chronic back pain.

Those who uphold the view that chronic back pain is the result of degenerative disc disease would make sense of these symptoms by considering the normal movements as somehow aggravating the underlying degenerative changes of the spine. If the onset of these symptoms occurred slowly over time, they might posit that normal movements have become painful because the degenerative changes of the spines are progressively degenerating.

Those who uphold the view that chronic back pain is due to central sensitization would make sense of the symptom by understanding that the nervous system has become stuck in a persistent state of reactivity. This persistent reactivity has subsequently made the nervous system highly sensitive, so sensitive that even normal activities, such as those listed above, are painful. Indeed, the sensitivity can be so great that even simple pressure, such as touch and hugs, can increase pain and mild bumps to the painful area can send patients through the roof.

A number of factors are leading this change in our understanding of the nature of chronic back pain:

• The proliferation of scientific studies and publications linking the brain and the rest of the nervous system to the onset and maintenance of chronic pain (see, for examples, Apkarian, Baliki, & Geha, 2009; Baliki, et al., 2006; Chapman, Tuckett, & Song, 2008; Curatolo, Arendt-Nielsen, & Petersen-Felix, 2006; Woolf, 2011).
• The explanatory nature of central sensitization explains not only the chronicity of pain, but also its psychosocial aspects, such as excessive fatigue, insomnia, poor concentration and short-term memory, gastrointestinal upset, anxiety, and depression (Meeus & Nijs, 2007; Wieseler-Frank, Maier, & Watkins, 2005; Yunus, 2007).
• Numerous studies show consistent findings that chronic pain rehabilitation, an interdisciplinary therapy that focuses on down-regulating the nervous system, is the most effective form of chronic pain management (see, for examples, Gatchel & Okifuji, 2006; Turk, 2002).
• In contrast, the explanation that degenerative disc disease is the cause of chronic back pain leads patients into the mistaken belief that their spines are fragile and inevitably going to worsen. This set of beliefs further lead patients to respond with behaviors that are more appropriate to acute injuries -- rest, inactivity, and extended use of narcotic pain relievers. When done over time, these behaviors can lead to fear-avoidance, de-conditioning, and disability (Leeuw, et al., 2007; Vlaeyen & Linton, 2000).
• Numerous studies show consistent findings that surgical and interventional procedures are largely, though not wholly, ineffective (Gibson & Waddell, 2007; Leclaire, et al., 2001; Mirza & Deyo, 2007; van Tulder, et al., 2006; van Wijk, et al., 2005; Weinstein, et al., 2006; Weinstein, et al., 2008). These procedures presume chronic pain to be the result of an orthopedic condition, specifically degenerative disc disease.
• While degenerative changes of the spine have some relation to pain, the correlation between such changes and pain is weak to modest, at best (Endean, Palmer, & Coggon, 2011). In the case of chronic back pain, these low correlations indicate that much is left unexplained when attributing the cause to degenerative changes of the spine.
• Numerous studies show consistent findings that degenerative disc disease is neither inevitably degenerative nor a disease (see, for examples, Carragee, et al., 2006; Hutton, et al., 2011; Jarvik, et al., 2005; Jensen, et al., 1994; Matsubara, et al., 1995; Takatalo, et a., 2009).

Knowledge in science advances when both different investigators consistently come to similar findings and, subsequently, a shift occurs in how the community of stakeholders sees and understands a particular phenomenon. In chronic pain management, the sheer numbers of data are all pointing to the same conclusion: the notion of degenerative disc disease does not explain the majority of the variance of chronic back pain symptoms, but rather the notion of central sensitization does. In other words, chronic back pain is a nervous system condition, not an orthopedic condition. Presently, we are witnessing this shift in our paradigmatic understanding of chronic back pain.  

References

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Author: Murray J. McAllister, PsyD

Date of last modification: April 29, 2013