The primary problem I treat as a Physiotherapist is pain. Despite the link between pain and sleep being extensively studied over the past few decades, I know little about what the research has found. What I've come to understand is that the bidirectional relationship between sleep and medical conditions such as cardiovascular disease extends also to psychological disorders and pain disorders.

So many of my patients have mentioned or described some of the symptoms of dysfunctional sleep, yet I never previously thought anything of it. I simply assumed it was a consequence of a lifestyle choice, medication side effect, and definitely an unmodifiable factor. Now I'm curious about how many people suffer from chronic or severe pain conditions and concurrent sleep disorders? How can we tell which is driving which?

Both sleep problems and pain are highly prevalent and persistent conditions creating a large medical burden on society and understanding link between the two will help guide further research and treatment options. Although it is widely accepted that the relationship between pain and sleep is bidirectional, causality is hard to determine (Sivertsen, et al., 2015). This should not distract us from remembering that the two are undeniably linked. The previous two blogs looked at the Importance of Sleep and Clinical Assessment of Sleep Disorders. This blog looks more closely at what we currently know from research about sleep and pain.

Every year the National Sleep Foundation conducts an American Poll to collect data about sleep and they choose a specific topic each year to further discuss. For 2015 the topic of interest was sleep and pain. What the data showed is that pain is associated with the feeling of not getting enough sleep. 64% of people without pain said they got enough sleep while only 46% of people with acute pain and 36% of people with chronic pain said they got enough sleep. Those who reported having inadequate sleep also described a negative impact on their mood, enjoyment-of-life, relationships, work productivity and other ADLs (Knuston, 2015).

Having pain is associated with a 20-30% increased likelihood of not getting enough sleep.

Impaired sleep is associated with increased pain sensitivity.

Sivertsen and colleagues (2015) investigated the association between sleep and pain sensitivity in adults, specifically the link between insomnia and pain. These authors used cold pressure tests (involving putting the dominant wrist and hand into cold water for a maximum for 106 seconds and measuring time to withdrawal and numeric rating of pain) and took measures of insomnia, bed time, rise time, time to get out of bed, psychological distress (Hopkins Symptom Check List), and chronic pain.

In the group with insomnia 43% reported psychological distress while in the control group only 6% reported psychological distress.
In the control group 70% of people could sustain 106 seconds in cold water and the average pain rating was 6/10.
In the insomnia group 58% of people sustained 106 seconds and the average pain rating was 7/10.

Sivertsen and colleagues (2015) suggested that insomnia can alter pain sensitivity through changes in levels of dopamine. Dopamine is a fundamental neurotransmitter for sleep-wake regulation and is involved in sleep-pain association.

All sleep parameters in the insomnia group where associated with reduced pain tolerance.

Chronic pain is associated with impaired sleep

Other studies investigating pain disorders and sleep use participants with chronic pain conditions such as temporomandibular joint disorder (TMD) and fibromyalgia. These pain conditions are known to have high degrees of central sensitisation, in which central pain processing mechanisms contribute to the amplification and perpetuation of pain. Sleep is a major central contributing factor. One key characteristic of central sensitisation syndromes is heightened pain sensitivity in affected and unaffected sites in the body.

Smith et al (2009) investigated the connection between TMD, sleep disorders and pain sensitivity and the results where staggering. 89% of participants met the ICSD criteria for at least one sleep disorder - 74% met the criteria for sleep-related bruxism, 36% for insomnia and 28% for sleep apnea. As mentioned above insomnia is associated with increased pain sensitivity and this study confirmed that statement. The subjects with insomnia and TMD had reduced heat pain threshold and pain pressure thresholds at higher levels compared to any other sleep disorder.

Fibromyalgia (FMS) is a chronic pain condition strongly associated with unrefreshing sleep, chronic fatigue and psychological distress (Moldofsky, 2008). There is both REM sleep and NREM sleep dysfunction associated with FMS.

REM sleep dysfunction is most strongly associated with increased waking pain sensitivity and interestingly REM sleep dysfunction reduces the analgesic effect of opiod medication.
In FMS increased arousal during NREM sleep has also been documented, which results in non-restorative sleep (Lautenbacher, Kundermann, & Krieg., 2006).

One of the main neurotransmitters thought to help improve non-restorative sleep and neural hypersensitivity is serotonin 5-HT (Lautenbacher, Kundermann, & Krieg., 2006; Moldofsky, 2008). This may be why SSRIs are now recommended in the treatment of many chronic pain conditions.

MAKE SLEEP A PRIORITY IN YOUR LIFE

Sleep deprivation is associated with disturbance in descending pain inhibitory control mechanisms and results in increased pain sensitivity.

Being in acute or chronic pain is more highly associated with an inadequate amount of sleep, so make it a priority to give yourself more time to get enough sleep.
Impaired sleep is associated with increased pain sensitivity - focussing on restorative sleep will help manage your pain levels. This is why sleep hygiene is so important.
Sleep quality is a strong predictor of next-day pain sensitivity but not the other way around. Meaning you can have an awful day in regards to pain and it doesn't predict poor sleep that night (Lautenbacher, Kundermann, & Krieg., 2006). Don't go to sleep worrying about how good it will be, just do your best to make the best environment to get enough and good quality sleep.
Improvement in sleep often proceeds and predicts improvement in pain (Koffel, et al., 2015). Focussing on making your sleep a priority will help your long term recovery.

The final blog in this 4-part sleep series is going to look at the functional overlap in neuroanatomy which further explains and expands on the bi-directional relationship between sleep and pain disorders.

Sian

References

Barthas, F., Sellmeijer, J., Hugel, S., Waltisperger, E., Barrot, M., & Yalcin, I. (2015). The anterior cingulate cortex is a critical hub for pain-induced depression. Biological psychiatry, 77(3), 236-245.

Buysse, D. J., Reynolds, C. F., Monk, T. H., Berman, S. R., & Kupfer, D. J. (1989). The Pittsburgh Sleep Quality Index: a new instrument for psychiatric practice and research. Psychiatry research, 28(2), 193-213.

Knutson, K. (2015). Sleep and pain: summary of the 2015 Sleep in America Poll. Sleep Health: Journal of the National Sleep Foundation, 1(2), 85.

Koffel, E., Kroenke, K., Bair, M. J., Leverty, D., Polusny, M. A., & Krebs, E. E. (2015). The Bidirectional Relationship Between Sleep Complaints and Pain: Analysis of Data From a Randomized Trial.

Lautenbacher, S., Kundermann, B., & Krieg, J. C. (2006). Sleep deprivation and pain perception. Sleep medicine reviews, 10(5), 357-369.

Moldofsky, H. (2001). Sleep and pain. Sleep medicine reviews, 5(5), 385-396.

Moldofsky, H. (2008). The significance of the sleeping–waking brain for the understanding of widespread musculoskeletal pain and fatigue in fibromyalgia syndrome and allied syndromes. Joint Bone Spine, 75(4), 397-402.

Parmelee, P. A., Tighe, C. A., & Dautovich, N. D. (2015). Sleep Disturbance in Osteoarthritis: Linkages With Pain, Disability, and Depressive Symptoms. Arthritis care & research, 67(3), 358-365.

Roehrs, T. A. (2009). Does effective management of sleep disorders improve pain symptoms?. Drugs, 69(2), 5-11.

Sivertsen, B., Lallukka, T., Petrie, K. J., Steingrímsdóttir, Ó. A., Stubhaug, A., & Nielsen, C. S. (2015). Sleep and Pain Sensitivity in Adults. Pain.

Smith, M. T., & Haythornthwaite, J. A. (2004). How do sleep disturbance and chronic pain inter-relate? Insights from the longitudinal and cognitive-behavioral clinical trials literature. Sleep medicine reviews, 8(2), 119-132.

Smith, M. T., Wickwire, E. M., Grace, E. G., Edwards, R. R., Buenaver, L. F., Peterson, S., ... & Haythornthwaite, J. A. (2009). Sleep disorders and their association with laboratory pain sensitivity in temporomandibular joint disorder. Sleep, 32(6), 779.