teeth because a child was continuously biting and producing skin erosions in the mouth. For some children with CIP, what should be pain is actually felt as a tingling that actually drives them to physically harm themselves because they find the sensation stimulating. This brings me back to my childhood. When I’d have a numb lip after a dental procedure, all I wanted to do was to keep biting it. Thankfully for me, that numbness was only temporary.
CIP isn’t the only way our capacity for pain can be lost. Diabetes, a chronic inability to correctly regulate blood sugar, can damage nerves when blood sugar levels are too high for too long. This nerve damage, called neuropathy, can cause patients to lose sensation in their feet and ankles. As with CIP, diabetic neuropathy makes the feet vulnerable to constant, repetitive stress due to walking or running. Because of the patient’s inability to sense the injury, ulcers can eventually occur. Decreased blood flow, also due to diabetes, combined with additional, unremitting pressure on the ulcer can result in infection. By the time these infections are detected, there is often erosion into the bones of the feet, culminating in osteomyelitis. This can result in the loss of the limb or the spread of the infection to other parts of the body.
Another threat to our protective pain response is leprosy. For most of human history, people believed that the disease of leprosy, widespread enough to be mentioned multiple times in the Bible, caused the body’s extremities to rot and fall off. But, as first discovered by the English physician Paul Brand, leprosy’s true effect is to damage the nerves that transmit pain.
After completing extensive work with leprosy patients in India, Brand noticed how patients with the disease would constantly injure themselves without realizing it, resulting in skin ulcers and trauma. One experience at the leprosarium opened his eyes to the effects of the disease, as he later related in his book, The Gift of Pain:
A woman…was roasting yams over a charcoal brazier…The yam fell off the stick, however, and I watched as she tried unsuccessfully to spear it, each jab driving the yam farther underneath the hot red coals. Finally, she shrugged and looked over to an old man squatting a few feet away. At her gesture, obviously knowing what was expected of him, he shambled over to the fire, reached in, pushed aside the hot coals to retrieve the yam, and then returned to his seat.
Aghast, Brand rushed over to examine the old man’s hands. He had no fingers left, only stubs covered in blisters and scars, the pain of which he seemed to be blissfully unaware. This experience led Brand to focus his efforts with leprosy patients on teaching them self-monitoring and constant vigilance. Without pain to warn them of damage to their bodies, they would have to rely on using their eyes. Once he’d successfully taught patients how to do this, the “rotting” effect of leprosy disappeared. Brand’s experiences with leprosy led him to dub pain “God’s greatest gift to mankind.”
Pain as Protector
In medicine, when we treat pain without deciphering the underlying cause, we are making a grievous error. It’s like shutting off the power to a burning building because the sound of the fire alarm is bothering you. You have to put the fire out. If the body heals on its own from injury, medical intervention isn’t necessarily needed, but when pain persists, the underlying cause must be resolved to restore balance. Once the problem is addressed, the pain has served its purpose, which is to get the person to identify the damage and deal with it.
When you get a small cut on your skin, you heal quickly and often with no visible mark. There may be a lesson to learn from this injury, such as avoid sharp objects. A deep wound, on the other hand, usually stays with you as a scar, a visible reminder of an injury in addition to the memory of the pain to remind you of what not to do next time. Pain teaches you to avoid a similar injury in the future by adjusting your actions and behavior.
“But why am I in so much pain for months after my injury?” Patients often ask me why their pain persists so strongly and for so long after an injury. They are frustrated at the slow healing process that limits their activity for weeks to months. I remind them that the pain remains to ensure that they are particularly careful around that part of the body so that it can heal completely.
When we see someone with a lot of scars, we infer that they have endured a lot of pain in their lives and that they are wiser and more experienced as a result. Scar tissue is used as a metaphor for physical or psychological trauma. When we learn from pain, we call it adaptive—it helps us adapt ourselves to the world.
Instead of looking at pain as a discrete, traumatic event, let’s try another perspective. Let’s say you’ve decided to start playing tennis. When you start practicing a new sport in earnest, it’ll hurt. Beyond general muscle soreness, your hands will hurt where you adjust the strings and grip of your racquet. When you swing your racquet, there will be friction in places where your hand grips the racquet. Over time, your fingers will develop tears and abrasions in these areas of greater than normal friction. Eventually, protective calluses will form over these areas. Thus, injury, pain, and healing lead to further protection through the adaptive process.
Pain helps us grow in awareness of our environment. Darwin would agree that children with CIP are at a significant survival disadvantage. They can’t help but repeatedly hurt themselves, causing tissue injury, and they typically die prematurely.
As much as I would like to be able to turn their pain off in order to end their suffering altogether, patients with chronic pain need their capacity for pain as much as ever. I have had numerous patients discover serious illness or injury thanks to pain, whether jaw pain from a tooth infection, abdominal pain from appendicitis, or flank pain from a kidney stone. Even though they had long wished they could turn off the alarm system, when these conditions were found and treated promptly, they were able to be thankful that they’d had it on.
The Cartesian Model of Pain
Let’s consider simple, anatomic reasons for pain, like a stubbed toe or a paper cut. In his Treatise of Man, 17th-century French philosopher René Descartes proposed the existence of a “hollow tube” transmitting the pain sensation from the location of the injury to the brain. Fundamentally speaking, today’s pain specialists concur with Descartes in that they believe:
1 Nerves detect a painful sensation.
2 Those nerves transmit a pain signal to the brain.
3 By interrupting that signal we can stop the perception of pain.
Thus, we inject substances or prescribe medications that reduce a nerve’s ability to transmit pain to achieve pain reduction.
This model works quite well for physical pain, or pain “with a cause.” It leads us to seek out a focal, physical source of pain and treat it. However, the Cartesian model fails miserably when dealing with the psychological aspects of pain. For example, a person on a battlefield can sustain a horrific injury and perceive little or no pain and then experience agony in the hospital afterward during a simple needle injection. (We’ll cover this idea more in Chapter 4.)
If we identify a physical pain generator, like an area of inflammation, we can treat it through a combination of techniques with the goal of improving the patient’s functionality and reducing the level of pain with the lowest-risk intervention. When we can’t find a clear pain generator, we come to the conclusion that the nervous system is sending a false alarm and we attempt to tone down the general sensitivity of the pain signaling system.
While Descartes was in many ways a visionary when it comes to pain, our ideas on the subject have evolved substantially since the 1600s. Patrick Wall, mentioned earlier, and Canadian psychologist Ronald Melzack proposed the gate control theory of pain in 1965. They described a series of nerve pathways (peripheral, spinal cord, and brain) that allow us to perceive pain. According to their theory, while a pain signal is transmitted, there is potential for gates to be opened along these pathways, allowing for modulation of the intensity of the pain signal.
Although there are shortcomings in the gate control theory of pain, there are some benefits to this conceptual model over the simple Cartesian view of simple circuits that are either on or off. More recently, others