Appendix B: Chronic Pain

INTRODUCTION

This appendix focuses on one of the most common scenarios in primary care—chronic non-cancer pain that does not have an easily identifiable physical source, and therefore is difficult to "fix" with simple interventions. Of course, as needed, arrange treatment for any clearly identifiable source that is not resolving with conservative measures. Examples of these include interventional treatments of severe persistent back pain due to verified disc herniation with clinically consistent exam findings, documented nerve impingements amenable to surgical release, or severe joint disease amenable to surgical repair or joint replacement.

But how should the practitioner approach the more common scenario, where their patient has chronic pain with no clearly identifiable lesion to fix, or their pain seems more widespread, out of proportion, or otherwise not correlating with or lasting longer than expected for any "nociceptive generator lesions" found? This scenario of chronic pain is common and increasing in prevalence, places an enormous burden on healthcare resources, is responsible for major loss of work productivity, causes untold misery to the patient, increases risk of many other chronic diseases, disrupts family and social life, and is a major driver of the opioid epidemic.

SCOPE

This appendix does not address specific issues in some important pain syndromes such as sickle cell anemia and chronic pancreatitis, nor does it specifically address palliative and end-of-life care issues (see Chapter 5, End of Life). While many of the principles reviewed here can be generalized to other chronic pain situations, the reader is encouraged to review standard resources for specific aspects of treating entities not addressed here.

KEY PRINCIPLES

Chronic pain is defined as pain persisting beyond the period of healing of the damaged tissues (sometimes arbitrarily set as >3 months). Much of nonspecific chronic pain is caused by alterations in the "psycho-neuro pain processing system" rather than solely or mainly due to persistent nociceptive input from a peripheral lesion. This type of chronic pain is believed to be a maladaptive psychophysiologic response. The pain processing neural networks get into a vicious cycle of danger-alarm triggering and facilitation leading to pain generation and hypersensitivity.^1,2 It is possible and common for the CNS pain processing neural networks to "learn" to manufacture pain with no actual nociceptive input from peripheral tissues, or to magnify any such nociceptive input to worsen pain. This pain is just as "real" as tissue injury–related pain. The patient's experience of pain produced by this subconscious psychophysiologic mechanism appears to be indistinguishable from pain due to a peripheral lesion; thus, misattribution of the source of pain is common, and it is critical to assess to effectively treat it. It is likely that much of the chronic pain syndromes seen in primary care are primarily due to this "psychophysiologic disorder" (PPD), also known by many other names such as mind/body and tension myositis syndrome.^...