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By Lucy Williams, Ivanhoe Health Correspondent
ORLANDO, Fla. (Ivanhoe Newswire) -- Insomnia and chronic pain seem to go hand-in-hand. Pain can disrupt sleep, but now researchers are asking, "Which comes first -- sleep disturbance or pain?"
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The answer may be both. Pain disrupts sleep, but recent research reveals sleep disruption might contribute directly to hyperalgesia, or extreme sensitivity to pain.
"Sleep fragmentation may actually causally contribute to chronic pain," lead author Michael Smith, Ph.D., of Johns Hopkins School of Medicine in Baltimore, told Ivanhoe. "It's not really a secondary symptom. It's an active symptom that requires active management to regulate the brain's way of managing and moderating pain."
Johns Hopkins University researchers studied the effects of sleep disturbances in women for seven nights. Participants were assigned to a control group, a forced awakening group or a restricted sleep opportunity group. Women in the control group slept undisturbed. Women in the forced awakening group were awakened eight times each night. Women in the restricted sleep opportunity group were deprived of sleep for 36 hours and then allowed 11 hours of recovery sleep.
Researchers assessed participant pain thresholds and pain inhibition. Women in the forced awakening group demonstrated an increase in spontaneous pain. The control group and restricted sleep opportunity group demonstrated no increase in pain response.
Researchers are not certain why sleep disturbances enhance chronic pain. Dr. Smith suggests sleep disturbances could impair the body's systems for regulating pain.
"That impairment system is thought to be opioid-driven," he said. "The hypothesis I'm pursuing is that sleep fragmentation, not just sleep loss, somehow impairs the endogenous opioid system, which is responsible for regulating pain."
Not only does an impaired opioid system inhibit pain regulation, it may also make drugs less effective.
"This type of sleep fragmentation might impair the opioid system, and it might make morphine and opioid-related drugs less effective," Dr. Smith said. "If this is the case, patients who get fragmentation would require more opioids to get the same effect. That's costly and there's more room for side effects."
Sleep deprivation is also associated with enhanced inflammation in the body, which could be another cause of pain.
"Sleep deprivation definitely enhances pro-inflammatory cytokines, and they're known to cause pain sensitivity," he said. "That would be one of the competing hypotheses."
These findings could be helpful for alleviating pain in hospital patients.
"If someone goes post-surgery and they have a lot of pain, the post-operative environment may actually be more conducive to hyperalgesia [pain sensitivity] and require more pain medications," Dr. Smith said. "Maybe what you need to do is modify the way you care for the patient and allow them to get 4 hours of solid sleep if it's medically feasible. If you can let them sleep four hours solid, that would be better than just sort of going in frequently to check bloods."
Further research is necessary to determine exactly why sleep disturbances enhance pain response.
This article was reported by Ivanhoe.com, which offers Medical Alerts by e-mail every day of the week. To subscribe, click on: http://www.ivanhoe.com/newsalert/.
SOURCE: Ivanhoe interview with Michael Smith, Ph.D.; SLEEP, 2007:30
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