The use of opioid painkillers might affect brain activity associated with responses of anticipated rewards and non-punishments in people with fibromyalgia, a pilot study suggests. This finding could help clinicians better understand the impact of long-term opioid use for the treatment of chronic pain.
The study, “Apparent Effects of Opioid Use on Neural Responses to Reward in Chronic Pain,” was published in the journal Nature Scientific Reports.
People with chronic pain, such as those affected by fibromyalgia, often develop kinesophobia — a fear or avoidance of moving.
For many of them, physical activity leads to pain, which will cause them to decrease their physical activity to avoid additional pain. This can be viewed as a maladaptive cycle of punishment (or pain) and reward (pain avoidance).
This is a barrier to treating these patients and improving their physical function and quality of life. A better understanding of the underlying neural mechanisms involved in this reward and punishment response can help develop better strategies to reduce or break the cycle.
While chronic pain can change the neural networks implicated in incentive processing, such as by reducing the activity of some brain circuits, painkillers (such as opioids) can also have an impact on these responses.
Current guidelines do not recommend the use of opioids to treat fibromyalgia because of myriad side effects, risk of addiction, and poor evidence of effectiveness. Still, many patients who take them report benefits similar to those of patients taking non-opioid painkillers.
Researchers from Stanford University evaluated how opioid use could modulate the neural response to reward in chronic pain.
They compared the neuronal network activity, as assessed by functional magnetic resonance imaging (fMRI), of 17 fibromyalgia patients taking opioids with that of 17 patients not taking opioids and 15 healthy volunteers. All participants underwent a monetary incentive delay (MID) task, which has been widely used to determine brain activity associated with reward and punishment responses.
Participants were asked to anticipate whether they could potentially win or lose small amounts of money, up to $5. This is known to trigger the neural networks of reward and punishment processing, outlining all its distinct aspects.
The team found that neural responses in the nucleus accumbens — one of the brain areas involved in processing responses — to anticipated reward and non-loss outcomes were similar between both fibromyalgia groups, and compared to healthy controls.
This relatively “normalized” response “to anticipated rewards and non-punishments” may be related to patients’ belief that opioids are beneficial, “despite other potentially negative influences of long-term opioid use on chronic pain,” researchers suggested.
However, neural responses in the medial prefrontal cortex — another brain area known to be involved — were significantly altered among patients with fibromyalgia not taking opioids compared to healthy controls. In contrast, patients taking opioids showed responses in this brain area similar to those of healthy individuals. Researchers wrote that, despite limitations, ” these preliminary findings suggest relatively ‘normalized’ neural responses to monetary incentives in chronic pain patients who take opioids versus those who do not.”
“The different neural responses between the non-opioid and opioid fibromyalgia groups could be due to several interacting factors across multiple psychological and neurophysiological domains,” they stated. “Expectations, shaped by both prior experiences and environment, can strongly contribute to different responses to medications.”
The team noted that “these findings may be controversial” and should not be extrapolated “to suggest that opioids may, or may not, be of value in the treatment of fibromyalgia.”