Understanding Chronic Pain
Most of the time pain serves as a critical part of our sensory system, and is therefore a necessary though unpleasant function of a healthy body. However, it is becoming increasingly clear that chronic pain may be more like a disease or pathology of the nervous system associated with abnormal responses in the brain and spinal cord.
In this light, chronic pain is both a common and serious medical condition. Chronic pain is serious because of the impact it has on every facet of people's lives and because for many persons, cures are unattainable. It is medical because, at its root cause, chronic pain is always connected with the body and the brain.
Acute pain responses
Acute pain is that initial sensation of warning and hurt that we all experience. It tells us immediately when we are injured and lets us know the location and most often even the amount of damage that may have occurred. Pain is one of the most vital of our warning systems because it tells us about tissue damage anywhere in the body. It triggers our protective systems of withdrawal (taking your hand out of the fire), rest (to allow the injured area to heal), protection (tensing up areas around an injury to prevent re-injury), avoidance (fear of the context of the injury to prevent doing it again), and even warning to others (shouting out). These are all critical activities for survival.
Those born with a rare condition that prevents the perception of pain (congenital analgesia) have a significantly decreased life expectancy due to unrecognized trauma and infection.
It is important to remember these properties of acute pain in order to better understand chronic pain. A variety of methods are used to try to help people manage chronic pain. While this management approach differs from that of acute pain, keep in mind that the physiological system underlying both is the same.
So no matter how much you read or are told about the differences between acute and chronic pain, and no matter how much you tell yourself that chronic pain does not mean something is terribly wrong (it is “hurt but not harm”), chronic pain will still mostly “feel” like tissue damage and injury. This does not mean you cannot better manage and even decrease the severity and impact of pain in your life, since in fact you can.
But the optimum pain management approach is not based on willing pain away, or pretending it isn’t there, but rather on making best use of the growing scientific knowledge of how pain is communicated and modulated (altered or modified) in the body and brain.
Chronic pain, which is often defined as continuous or intermittent pain lasting longer than six months, afflicts an estimated 30 million to 50 million Americans. The social costs in disability and lost productivity totaling more than $100 billion annually.
Pain is the number one problem that brings patients to doctors, as well as to complimentary or alternative medicine (CAM) practitioners. The tremendous suffering caused by chronic pain is not measurable in dollars and almost all of us know at least one person who is struggling with chronic pain.
Pain leads to disability and emotional suffering. Moreover, evidence is accumulating that some types of chronic pain may be damaging to both the nervous system and even the immune system.
Pain transmission and modulation
Although much remains to be known, research over the past three decades has revealed key information about pain and our bodies’ response, and this has led to improved treatment in many areas.
Acute pain usually begins with activation of specialized nerve endings (nociceptors) located throughout the body, almost everywhere except for the brain. They respond exclusively to tissue-damaging stimuli like, excessive heat, cold, tearing, or pressure. Various chemicals, such as prostaglandins and stress related hormones, can sensitize nociceptors. (Aspirin-type pain relief medications (NSAIDs) work by blocking the prostaglandins.)
The pain signal then travels along special nerve fibers to the part of the spinal cord called the dorsal horn. From there, the pain ascends to the various brain structures.
Although this pain transmission system was once thought to operate like an old-time telegraph (messages input at one end and arrive at the other), we now know that the system is much more like a powerful computer.
In order to enable our body to have the best information when it is needed, signals coming in are highly modulated. This means pain signals from specific areas can be amplified, suppressed, or altered in quality in the spinal cord or brain.
For the most part this works to our great advantage. For example, after stubbing your toe, the pain, which is an acute signal to check for damage, quickly dulls. This is an active process of pain suppression to allow us to return to other actions. In a similar way, most of the activity going on in our gastrointestinal tract (including very large muscle contractions) is not felt due to active suppression. On the other hand, pain might continue to remind us to avoid active use in an injury in which movement may be harmful.
The gate control theory states that nerve impulses, evoked by injury, are influenced in the spinal cord by other nerve cells that act like gates, either preventing the impulses from getting through, or facilitating their passage. In other words, the brain is not a passive receiver of pain information but can influence the information received.
—Dr. Ronald Melzack
The description of our own built-in pain modulation system (called the gate control theory) by Drs. Melzack and Wall in 1965 and the subsequent discovery of internal opiate-type chemicals (such as the endorphins) were major first steps in a fuller understanding of pain control within the body.
More recently, many more parts of this complex system have been uncovered, as well as new chemical transmitters and interactions between pain modulation and other parts of our sensory and emotional brain systems.
Pain and threat
We have known for a long time that pain is not a simple sensation and that it is intimately linked with our inborn emotional systems for detecting and responding to threat. In this way it is closely tied to the same fear or “fight or flight” system that responds to external threats. Any sound or object may be associated with a fear response, but pain is unique in that it always has a negative emotional quality (unpleasantness) and is closely associated with emotions of fear and anxiety.
The power of learned associations between specific painful sensations and emotional reactions is dramatic. Once set in place, these conditioned responses operate regardless of the context and without conscious input.
In a similar way, pain or even the context – the time, place, or circumstances – surrounding a painful episode may perpetuate a pain-fear-pain cycle. Some of the brain circuits underlying this pain-fear cycle have recently been made clear using functional brain imaging for pain problems both in the internal organs and the rest of the body.
Connections between the emotional and pain systems may also account for the often successful use of anti-anxiety and anti-depression medications to treat chronic pain.
Chronic pain management
In chronic pain we have strong evidence that our pain modulation system is not working well. Instead of suppression, the system may be over-sensitized so that even normal sensations trigger pain transmission and suffering. As a result of the pain, people may also have increased levels of anxiety and depression, decreased quality of life, fear of further pain and disability, sleep loss, and withdrawal from social and pleasurable activities.
The above discussion might lead one to feel helpless in the face of such an important and powerful physiological system that has gone astray. The better news is that both ancient and modern medicine has evolved a variety of ways to help cope with chronic pain – and maybe even return the system to more normal functioning.