Disrupted Sleep Linked to Lower Pain Tolerance, Impulsivity

Nancy A. Melville

May 18, 2016

AUSTIN, Texas — Healthy people exposed to disruptions in sleep, similar to those commonly experienced in chronic pain, show significant decreases in pain tolerance and higher impulsivity, underscoring the important role of sleep in chronic pain, new research suggests.

"We must be circumspect in extracting clinical implications from these findings because the study was conducted in a healthy sample with only a single night of sleep deprivation, [however], in general, the findings broadly support the notion that sleep loss increases pain sensitivity," first author Emelie L. Modalen, from the Department of Psychiatry and Behavioral Sciences at Johns Hopkins University School of Medicine, Baltimore, Maryland, told Medscape Medical News.

The findings were presented here at the American Pain Society (APS) 35th Annual Scientific Meeting.

The study involved 35 healthy individuals without sleep disorders who were randomly assigned to the opportunity for 8 hours of uninterrupted sleep or to a night of forced awakenings, consisting of seven 20-minute awakenings and one 60-minute awakening during the 8-hour period of attempted sleep.

The participants had a mean age of 28 years and were evenly divided by sex.

All participants completed a cold pressor task the following day, consisting of immersing their hand in a cold water bath (4°C) and removing it when the pain became intolerable, or up to a 5-minute time limit.

Participants also completed the 13-item Pain Catastrophizing Scale, self-reporting on a 5-point scale measures of helplessness, magnification, and rumination.

In the crossover study design, the participants then returned a minimum of 2 weeks later for the opposite sleep condition and underwent repeat testing, with testing hands counterbalanced for the second session.

Participants showed significant reductions in the amount of time they were able to tolerate the cold water bath after a night of forced awakenings (29.27 ± 2.66) compared with a night of uninterrupted sleep (45.85 ± 10.14; P < .05).

The night of forced awakenings was associated with a slight increase in pain catastrophizing (11.4 ± 2.21) compared with uninterrupted sleep (10.9 ± 2.0); however, the difference was not statistically significant (P = .56).

"The null finding on catastrophizing may be reflective of the insensitivity of the measure in healthy subjects with no prior experience with chronic pain," Modalen said.

"In addition, our subjects were rigorously screened to be free of psychopathological symptoms, including anxiety." Different results might be seen in a sample of patients with chronic pain, she noted.

The research was part of broader, ongoing research at Johns Hopkins using the disrupted sleep model, which was reported last year in a study http://www.journalsleep.org/ViewAbstract.aspx?pid=30292 in the journal Sleep to have a more negative effect on positive mood than partial sleep loss.

Another analysis from the team, presented at last year's APS meeting, showed that people exposed to disrupted sleep did not have the kind of reductions in pain responses after exposure to positive stimuli (images) that have been shown to otherwise occur after normal sleep, yet, interestingly, no differences were see in responses to negative images (P < .001), said Patrick Finan, PhD, assistant professor at Johns Hopkins Department of Psychiatry and Behavioral Science, who was senior author on that and the other disrupted sleep studies, in a talk at the meeting.

"We're seeing a blunting of the experience of positive affect without accompanying augmentation of negative affect," Dr Finan said.

"Basically, forced awakening is deflecting attention away from the positive stimuli without augmenting attention toward negative stimuli, which is consistent with what people tell us they are feeling."

The researchers have been looking into the hypothesis of sleep continuity disruption having an effect on mesolimbic dopamine processing and the reward system, which could have dramatic consequences for people with chronic pain, Dr Finan said.

"People are losing the positive emotional stores they need to be able to cope with pain flares that are needed on a day-to-day basis, and this could result, potentially, in a clustering of the disorders that we commonly see — this triad of chronic pain, insomnia, and depression, — may be supported by disrupted dopaminergic processes that sleep regulates."

Other findings from the research group suggest that that cluster also appears to include impulsivity. Dr Finan described that the same patients who showed deficits in positive affect functioning after disrupted sleep also showed impulsivity on a delayed money reward task, using real money.

In the task, participants are given the choice of a larger amount of money, such as 80 cents, in a minute and a half, or 20 cents immediately.

They found that participants were significantly more likely to choose the more impulsive option — the immediate 20 cent reward — following a night of disrupted sleep (P = .001), Dr Finan reported.

"You'd think if they knew they would be in the lab all day and had plenty of time they would pick the higher, delayed reward, but that's not what was observed," he said. "We're seeing real differences as a result of forced awakening, in this case, a greater impulsivity as measured by a lower indifference point."

Collectively, the findings underscore the unique challenges that could be involved in the treatment of the many chronic pain patients with sleep disorders.

"You can imagine that you're trying to engage patients in an intervention where the goal to increase positive emotions," Dr Finan said. "If their sleep is chronically disrupted and they are perhaps neurobiologically compromised and unable to generate positive emotions that we're trying to get them to do in therapy, then they're going to be hitting a wall."

"The pain will continue to flare, and people will lack the resources to combat that."

Positive Mood

While numerous studies have looked at the relationship between poor sleep and negative mood, the new research uniquely considers positive mood, Emily J. Bartley, PhD, a research assistant professor with the Pain Research & Intervention Center of Excellence at the University of Florida College of Dentistry in Gainesville, told Medscape Medical News.

"What makes Dr Finan's work particularly novel is that he investigated the impact of sleep disruption on both positive and negative emotions," said Dr Bartley, who moderated the session.

"When you interrupt a person's sleep to a degree that may be similar to what is experienced in chronic pain, it leads to a greater reduction in positive mood (as compared to a greater increase in negative mood), and the ability by which positive emotions buffer pain is dampened."

Overall, the findings suggest that disturbances in the circuitry involved in positive emotions could represent a mechanism by which sleep promotes and maintains pain, she added.

"In other words, disrupted sleep may set the stage for problems in the regulation of positive mood, and the failure to inhibit pain via positive emotions could increase risk for chronic pain development."

"Studies such as these could increase understanding about the mechanisms that underlie the sleep and pain relationship, which could lead to more refined treatments for patients who have concomitant sleep and pain difficulties."

The findings further offer clues in the clinical management of sleep disorders in pain, such as cognitive-behavioral therapy for insomnia (CBT-I), Dr Bartley noted.

"This type of treatment may be especially relevant to people with chronic pain, as sleep disturbance is prevalent in this population."

"Given the findings associated with Dr Finan's work, it also may be beneficial to supplement these treatments with approaches designed to increase positive mood and emotions."

Emelie Modalen has disclosed no relevant financial relationships. Dr Finan is a consultant to PainCare LLC.

American Pain Society (APS) 35th Annual Scientific Meeting. Abstract 190. Presented May 13, 2016.

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