Chronic pain can seriously affect the quality of life of a person, and it is often experienced by patients with medical conditions such as fibromyalgia, chronic fatigue syndrome, and rheumatoid arthritis. Now, researchers say that the use of the opioid morphine has only limited therapeutic value for controlling pain in these patients.
The results of the study were featured in an issue of the journal Pain Practice.
The sensitivity for pain in fibromyalgia and chronic fatigue syndrome depends largely on the function of central pain mechanisms — pain inhibitory and enhanced pain facilitatory mechanisms. Several studies have tried to find the underlying processes behind chronic pain, but depending on the illness, different systems seem to be involved.
Patients with chronic fatigue syndrome and fibromyalgia often have widespread hypersensitivity to pain due to a malfunction of the processes that control pain in the central nervous system (CNS), called central sensitization. This is when pain itself modifies the way the CNS works, and the patient gets more pain with less provocation. Rheumatoid arthritis patients, however, have pain caused by altered pain modulation processes.
Drug prescriptions to reduce pain are common, but the response to these drugs varies greatly.
Understanding how patients with different conditions respond to the same medication can help researchers identify the differences and similarities of the nature of chronic pain, and may help identify the best treatment for each condition.
In the study, titled “Influence of morphine and naloxone on pain modulation in Rheumatoid Arthritis, Chronic Fatigue Syndrome/Fibromyalgia and controls: a double blind randomized placebo-controlled cross-over study,” researchers from Belgium compared the effects of opioid-mediated pain inhibition in rheumatoid arthritis patients with those seen in patients with chronic fatigue syndrome or fibromyalgia.
The clinical study (NCT01154647) included 10 patients with chronic fatigue syndrome or fibromyalgia, 11 patients with rheumatoid arthritis, and 20 healthy pain-free individuals as control.
The chronic pain patients received an opioid-based drug — morphine — or a placebo. The healthy volunteers underwent the same procedure but with naloxone instead of morphine. Naloxone is an approved nonselective opioid antagonist medicine used to counteract the effects of an opioid overdose.
The results of the study showed that patients in the chronic pain group had lower pain thresholds compared with the healthy control group.
Morphine was found to increase the pain threshold of chronic pain patients compared to the control group. But this effect was similar to that observed in the group of pain patients treated with a placebo.
According to the team, the results showed that morphine was able to decrease the sensitivity to pain (it has an anti-hyperalgesia action) in patients with chronic fatigue syndrome, fibromyalgia, and rheumatoid arthritis. “Nevertheless, these effects were comparable to placebo,” researchers wrote.
Overall, the findings suggest the effects of morphine in modulating central sensitivity in patients with chronic pain is limited, and that “treatment of central sensitization may necessitate a combination of different acting pharmacological and non-pharmacological treatments,” the team concluded.