What is chronic pain and why is it hard to treat?

What is chronic pain and why is it hard to treat? | June 2016 | by Robert Caudle | Professor of Oral and Maxillofacial Surgery, Neuroscience Division, University of Florida

Here’s a rare article by a doctor that understands the severity of chronic pain and it’s devastating impact.

Our main therapies [for pain] are non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or aspirin, which are just modern versions of chewing on willow bark; and opioids, which are derivatives of opium.

Opioids are used to treat chronic pain not because they are the ideal treatment, but because for some patients, despite their drawbacks, they are the most effective treatment available at the moment.

The problem, as I see it, is this: we are not investing enough in researching and teaching what causes pain and how to treat it.  

Pain can have a purpose

What concerns those of us who treat and study pain, however, is chronic pain. This type of pain – that can last for weeks, months or even years – serves no useful purpose for survival and is actually detrimental to our health.

There isn’t one type of chronic pain.

In many cases chronic pain persists after an injury has healed. This happens relatively often with wounded veterans, car accident victims and others who have suffered violent trauma

Chronic pain from arthritis is telling the person about the damage in their body. In this respect it is similar to acute pain and, presumably, if the body healed the pain would subside. But, at the moment, there is no treatment or intervention to induce that healing so the pain becomes the most troubling aspect of the disease.

Chronic pain can also arise from conditions, like fibromyalgia, which have an unknown cause. These conditions are often misdiagnosed and the pain they produce may be dismissed by health care professionals as psychological or as drug-seeking behavior.

How do we experience pain?

The human pain experience can be divided into three dimensions:

what pain researchers call

  1. the sensory-discriminative,
  2. the affective-motivational and
  3. the cognitive-evaluative.

In acute pain there is a balance between each of these dimensions that allows us to accurately evaluate the pain and the threat it may pose to our survival. In chronic pain these dimensions are disrupted.

The sensory-discriminative dimension refers to the actual detection, location and intensity of the pain. This dimension is the result of a direct nerve pathway from the body to the spinal cord and up into the brain’s cortex.

Knowing where it hurts is only part of experiencing pain.

Do you need to run away or fight back? This is where the affective-emotional dimension comes in. It arises from the pain circuitry interacting with the limbic system (the emotional centers of the brain).

This pathway evokes the anger or fear associated with the possibility of physical harm. It also provokes learning so that in the future we avoid the circumstances leading to the injury.

The third dimension, the cognitive-evaluative, is the conscious interpretation of the pain signal, combined with other sensory information.

When it always hurts

The pain sensory system is designed for survival. If a pain signal persists, the default programming is that the threat to survival remains an urgent concern.

To increase the urgency of the pain signal, the sensory-discriminative dimension of pain becomes less distinct, leading to a more diffuse, less localized, pain. This pathway also amplifies the pain signal by rewiring spinal cord circuits that carry the signal to the brain, making the pain feel more intense.

In chronic pain, as compared to acute pain, the affective-motivational dimension becomes dominant, leading to psychological consequences. Thus suffering and depression are much worse for chronic pain patients than it would be for an individual with an equivalent acute injury.

The multifaceted nature of pain is why opioids are often the most effective agents for both moderate to severe acute and chronic pain.

Opioids act at all levels of the pain neural circuitry. They suppress incoming pain signals from the peripheral nerves in the body, but importantly for chronic pain patients, they also inhibit the amplification of the signals in the spinal cord and improve the emotional state of the patient.

I don’t entirely agree with this last one about improving a patient’s emotional state.

I think he believes the common and erroneous belief that we feel the euphoria that abusers do. But this only happens if a person takes more opioids than needed to fight the pain. (See Opioids, Endorphins, and Getting High)

Legitimate patients with incurable and disabling chronic pain generally try to use as low a dose as they can because we know we’ll probably need them for the rest of our lives.

Funding for pain research lags

In 2015 the National Institutes of Health spent $854 million on pain research, compared to more than $6 billion for cancer.

It is no wonder that pain patients muddle through with what amounts to centuries-old therapies.

The competition for funding for pain researchers is intense. In fact, many of my friends and colleagues, all highly experienced midcareer scientists, are leaving research because they cannot sustain the funding necessary to make any significant progress in finding treatments for pain.

The dearth of funding is also discouraging young scientists from doing pain research.

The majority of studies lately are about addiction to opioids, not pain. 

These researchers aren’t trying to find a cure for either addiction or pain but are just generating more media-hyped headlines about the evils of opioids.

With tenure at major universities becoming more and more difficult to attain, they can little afford to spend all of their time writing research proposals that do not get funded.

Unrelieved pain contributes more to human suffering than any other disease.

It is time to invest in research to find safe effective therapies and on training health care providers to appropriately diagnose and treat pain.  

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