Chronic Pain Alters Experience of Acute Pain


Chronic Pain Alters Experience of Acute Pain

By Crystal Phend, Senior Staff Writer, MedPage Today Published: April 16, 2010 Reviewed by Dori F. Zaleznik, MD; Associate Clinical Professor of Medicine, Harvard Medical School, Boston and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner

Chronic pain may reverse the neural response to acute pain in some ways, researchers found.

The central nervous system sensory activation patterns and subjective sensation of pain were largely identical between healthy volunteers and chronic back pain sufferers in a brain imaging study reported in the April 15 issue of Neuron.

The difference was in how the nucleus accumbens region of the brain interpreted acute pain as a motivation for behavior, according to A. Vania Apkarian, PhD, of Northwestern University in Chicago, and colleagues

At the end of a painful heat stimulus, this portion of the brain registered phasic activity in chronic pain patients with the opposite polarity of that seen in healthy adults.

Although removal of a painful sensation usually registers as a reward, among chronic pain patients it actually appeared to reflect a predicted punishment, the researchers explained.

Acute pain robustly reduced the level of chronic pain perceived (P<0.004), such that its end predicted worsening of ongoing back pain, they suggested.

Apkarian’s group called this a potential “dysfunctional associative learning process” involved in the transition from acute back pain to chronic back pain.

The switch in the brain’s prediction and valuation of the pain — mediated by the nucleus accumbens and related circuitry — likely plays a role, not in the actual sensory perception, but in the internal state as “an integral component of the pathophysiology of chronic pain,” they wrote in Neuron.

Other changes have been shown in chronic pain in prior studies, including abnormal brain chemistry, regional gray matter atrophy, cognitive changes, and unique patterns of brain activity.

However, the phasic activity in the nucleus accumbens at the end of the painful stimulus was unique, they said.

For the study, the researchers imaged the brain using functional MRI while administering a pseudo-random series of nine thermal stimuli ranging from 47° to 51°C of 12 to 30 seconds each in 16 healthy adults and 16 patients with physician-diagnosed chronic back pain.

An additional eight chronic back pain patients rated chronic pain and pain associated with the stimuli but without MRI imaging.

During the fMRI tests, brain activity during the period when the heat was being applied and the pain reported from it was similar between groups.

But healthy individuals showed higher nucleus accumbens activity in the period when the thermal heat was decreasing and the pain was coming to an end compared with chronic pain patients (P<0.0001).

This difference at offset of pain distinguished the two groups with 100% sensitivity and 100% specificity, “implying that this signal can be used as an objective marker of chronic pain,” Apkarian’s group wrote.

Nucleus accumbens activity during this stimuli offset period appeared to be influenced from differing cortical sources between the two groups, too.

Activity in the insula best represented the magnitude of pain perception in this period among healthy controls. Meanwhile, the nucleus accumbens in chronic back pain patients was more strongly connected with activity in the medial prefrontal cortex — a brain area implicated in valuation, action selection, and pain modulation.

Chronic pain patients also had a higher poststimulus baseline activity (both P<0.0001), a difference that had 60% sensitivity and 66.7% specificity in distinguishing them from healthy volunteers.

The study was funded by a grant from the National Institute of Neurological Disorders and Stroke.

The researchers provided no information on conflicts of interest.

Primary source: Neuron Source reference: Baliki MN, et al “Predicting value of pain and analgesia: Nucleus accumbens response to noxious stimuli changes in the presence of chronic pain” Neuron 2010; 66: 149–60.

http://www.medpagetoday.com/Neurology/PainManagement/19572

1 Comment

  1. My Neuro Mucular Therapist would attempt to realign my body. I would not be free of pain directly after. I would be fine during and after. Usually, she would ask the scale of 1-10 questions. I was able to handle anything she could dish out. She said I had a very high pain threshold. She felt that I handled the pain of treatment better than any of her adult patients. I was 14 at the time. I remember hours after feeling as if she had in a sense lowered my ability to control the pain and my pain threshold. I would become hostile and overwhelmed as I felt that she had lowered the one protection I had, the ability to keep the pain as calm as possible. This was dissimilar to getting my fascia released or an intense massage that released the built up toxins and stretching muscles out that are way beyond normal stiffness. It was painful and the fascia release of my chest to shoulder area made it hard to get out of bed raising myself up, etc.. for a few days. It was not the same thing at all. I used to love the sweet ache after a workout. It was a good pain. It would not abate my constant pain it gave me another type of pain to focus on. One that did not plague and torment me to such an unbearable level without surcease or abatement. I do wish I could still work out for the positive benefits. Unfortunately, that was 22 years ago and I no longer have any conditioning. I don’t leave my house and I must stay reclined or suffer tenfold. Even a drop of water knows to jump off a hot skillet. After 22 years the primal response to avoid pain can make any person home bound and on permanent bed rest as our bodies further degenerate creating such an insidious and nasty cycle. I cannot face social interaction due to overstimuli. Exacerbated by my own self-loathing of my perceived failures in the face of adversity allowing my body to degenerate further and no longer able to work or contribute in any way to my community or society. My favorite pleasure in life has been to make others feel better, safe and heard. I digress, this article was over my level of understanding I wanted to see if this phenomena sounded in anyway like my experience. I have had to tell massage therapists that they need to dig into my shoulders as hard as they can. If I could reach my shoulders and had enough strength in my arms and hands I would dig in so hard that most would run screaming from it. Is this similar to the aricle’s meaning? Or, am I so offended by the never ending intensity of my pain that I wish to beat it out of me, excise it and release the metaphorical screws that never stops twisting, tighter and tighter?

    Liked by 1 person

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