What's the Cause of Chronic Pain?

Chronic pain affects the personalities, moods and memories of millions of people. Knowing why is crucial to finding a cure.

Woman holding neck in pain

 

In this first part of a two-part series, we examine what causes chronic pain. In part two, we’ll look at cutting-edge methods in the treatment of chronic pain, and how patients can advocate for themselves.

An estimated 50 million U.S. adults are living with chronic pain, according to a report issued by the Centers for Disease Control and Prevention (CDC). That equates to more than 20% of the population.

Pain can significantly affect an individual’s sense of self and personality, in addition to their ability to be active and mobile. In the most severe cases — a full 8% of the population, according to the report — pain can change the person’s ability to work or be successful in school. And people in pain often find themselves withdrawing from friends, family and social activities they once enjoyed.  

To better understand this phenomenon, we talked with chronic pain experts who explain the reasons behind what you or a loved one might be experiencing. 

James Giordano, Professor of Neurology and Biochemistry at Georgetown University Medical Center, has spent nearly 40 years studying chronic pain and its causes, treatments and effects. Giordano says pain affects people’s lives by changing their physiology, which often thrusts them into a cycle of pain, dysfunction and disability that is hard to break. “Chronic pain can change the brain,” Giordano explains. “It becomes important to be able to understand that because, many times, chronic pain patients don’t seem to have anything wrong with them, other than they report devastating chronic pain.” 

What exactly is chronic pain?
The simple and widely-accepted definition of chronic pain is pain that lasts for more than three months, says Tor Wager, Diana L. Taylor Distinguished Professor of Psychological and Brain Sciences at Dartmouth University. “Most forms of pain go away,” Wager says. “We still have a lot to learn about what goes wrong in individuals when pain becomes chronic.”

The difference between chronic pain and acute pain (what is often thought of as “regular” pain) is that, with acute pain, the brain ties the sensation of pain to the cause and makes a decision about how the body should react in order for the pain to stop and avoid injury. Chronic pain, however, can be confusing because the underlying cause may be unclear.
 
Giordano says that chronic pain developed as part of the biological and evolutionary processes out of which humans evolved. “The purpose of chronic pain is to impede the organism sufficiently to recover from apparent damage to its body. If something is going to hurt continuously, something is probably broken or injured for a long period of time. Very often, rest is required. Chronic pain can activate a variety of brain mechanisms that are involved in slowing the organism down. They become sleepy and there is engagement of the immune response, as well as inflammatory and tissue repair responses. This is an attempt to mobilize resources in the body to repair whatever is injured so the individual can recover.”

Despite the body’s best attempts, however, sometimes the pain can continue unresolved if the root problem and its effects are not addressed holistically.
 
What causes chronic pain?
Many people with chronic pain experience pain in a local site, such as the back, knee or neck, but oftentimes an examination or imagery of the painful area will reveal there is apparently nothing wrong, according to Wager. Instead, there are other contributing factors, such as when the pain receptors in a local pain site become more sensitive. 

This increased sensitization can continue on up through the spinal cord and into the brain itself, Wager says, “in the pathways that make us feel pain, but also in the pathways that make us feel vigilant about pain and avoidant about pain, and make us have the sense of distress or discomfort.” 
 
Giordano explains that in the bodies of people with chronic pain, “The change in the firing patterns involved in transmitting pain up the spinal cord to the brain become overactive. And through this over-activity, they become hyper-sensitized. Now they become responsive to non-painful input: They may develop Allodynia — painful sensation from non-painful inputs or non-painful stimuli — or hyperalgesia (excess pain) a condition in which any pain now becomes worse.”
 
How does chronic pain affect the brain?
The intensity and longevity of pain can actually change the way the body feels pain and responds to it.

“The pain transmitting system in the spinal cord, brain stem and brain becomes not only over-active but spontaneously active. So now it’s transmitting even though there is no input,” Giordano says. “And what happens with time is this system can remodel itself. The connectivity between the pain transmitting nerve cells actually becomes stronger and more active. The capacity of the body to modulate and turn that functionality down becomes weaker. And there can be structural changes in the nervous system from the very small to the fairly broad scale. The systems that transmit pain are also interacting with systems that don’t deal with pain, and as a result there is a broader array of sensitivities to various stimuli.”
 
The area of the brain that processes pain also directs the way people move, as well as our memories and emotions. With so many aspects of the self affected, pain can overwhelm the person experiencing it, even though medical providers may not initially be able to pinpoint a cause or find an effective treatment. 
 
Giordano says that often, people experiencing chronic pain “will be told that pain is all in their heads. In some cases – it is, but not because it’s imagined or fictional. At some point, pain becomes a brain event. But that doesn’t mean it doesn’t exist. The brain is being functionally activated. In that pattern of brain activation, you perceive pain as a result of abnormal excitation of the brain networks that produce pain. So indeed, it’s all in your head, but it’s a brain event caused by aberrant neurological transmission. It is real because your reality is how your brain perceives your body and your world.”

Lorinda Toledo is a writer and journalist in Los Angeles.