Pain and sleep I have been lecturing on the link between sleep and pain since 2004 but while it seems obvious that pain can cause sleep disturbance, the role of sleep in pain is perhaps less well known. Many British adults are affected by chronic pain and many of these suffer poor sleep as a result. Lack of sleep can impact all aspects of our physical, mental and emotional life. Because pain, like irritability of brain, perpetuates and intensifies itself. If you have gained a respite of either in sleep you have gained more than the mere respite. Both the probability of recurrence and of the same intensity will be diminished, whereas both will be terribly increased by want of sleep. This is the reason why sleep is so all-important. Florence Nightingale, Notes on Nursing, London 1859 Pain is a complex physiological process. When there is damage to the body, specialised nerve cells known as nociceptors, aka pain receptors, send a message to the brain via the spinal cord. Once the brain has received and interpreted the pain message, it coordinates an appropriate response; for instance, the brain can send a signal back to the spinal cord and nerves to decrease the severity of pain by releasing natural painkillers known as endorphins. Types of Pain In general, pain is divided into two categories: acute and chronic. In an acute pain episode, e.g., burning yourself on the stove or stubbing your toe, the pain resolves once the injury heals. However, sometimes your body heals, but your brain continues to perceive the pain. If the pain persists beyond the body’s normal healing time, then the pain is considered chronic. In some cases, chronic pain is due to an ongoing medical condition, such as arthritis or cancer, but often it may not have an identifiable cause. There are there main types of chronic pain; somatic, visceral and neuropathic. Somatic or bodily pain originates in the skin or muscle tissue and is often described as sharp, aching, throbbing, or gnawing. Visceral pain is associated with an internal organ, e.g., stomach, and is usually described as deep and aching. Neuropathic pain results from damage to a peripheral nerve(s), the spinal cord or the brain and is most often described as a burning or stabbing sensation. Pain causes poor sleep; poor sleep increases pain perception, so if sleep is not improved, then pain cannot be optimally reduced. Pain is one of the most frequent causes of poor sleep. In pain, patients’ difficulty sleeping ranks as one of the most reported conditions resulting in moderate to severe discomfort, at nearly twice the incidence of symptoms such as depression and anxiety. It is estimated that 50% to 89% of patients with chronic pain demonstrate sleep disturbances. And the severity of pain is linked to the quality of sleep; the more severe the sleep disturbance, the more intense the pain. (Rejas et al. European Journal of Pain. 2007;11: 329–340) Many patients suffering from chronic pain experience poor sleep quality, at least as significant as patients with primary insomnia. (Smith et al. J Behav Med. 2000;23(1):1-13) The poor quality of sleep results in diminished daytime functioning and can ultimately lead to emotional, physical, and financial burdens. Therefore it is essential to take sleep disturbance seriously. However, while sleep disturbances may be highly prevalent in pain patients, sleep disorders in individuals with chronic pain remain underreported, underdiagnosed and undertreated. (Stiefel and Stagno, CNS Drugs 2004) Importance of sleep in chronic pain Because of the numerous different pain conditions, few specific effects on sleep are common to all pain states (Drewes AM, Arendt-Nielsen L (2001) Pain and sleep in medical diseases: interactions and treatment possibilities (A review). Sleep Res Online 4(2):67–763). However, the general effects of pain on sleep can be summarised as an overall reduced sleep efficiency with altered sleep architecture characterised by increased wakefulness, increased stage N1 sleep, diminished slow-wave sleep, and, in some pain conditions, reduced rapid eye movement sleep (Onen SH, Onen F, Courpron P, Dubray C (2005) How pain and analgesics disturb sleep. Clin J Pain 21(5):422–431) Chronic pain activates and maintains CNS areas responsible for the awake state and dampening brain areas responsible for initiation and maintenance of sleep. In turn, lack of sleep may impair healing, leading directly to more pain and affects CNS areas responsible for coping mechanisms involved in dampening the experience of pain. This results in a vicious cycle with sleep disturbance and chronic pain maintaining and augmenting each other. (Call- Schmidt, Richardson. Prevalence of sleep disturbance and its relationship to pain in adults with chronic pain. Pain Manage Nurs 2003;4:124-33) Pain reduces the overall quality of sleep, increasing the amount of wakefulness during the night, increasing the amount of the lightest stage of sleep, and reducing deep, restorative sleep. (Onen et al. 2005 The Clinical Journal of Pain Volume 21 (5) 422-431). Chronic pain patients have more and more severe insomnia than pain-free patients (Marcus DA. Neuropathic Pain: A Primary Care Guide to Practical Management. 2nd Edition. Totowa, N.J.: Humana Press) It is important to note that pain, anxiety/depression and sleep problems involve the same neurotransmitters and neuro-anatomy. So it is not surprising that they co-exist in many patients. This triad of symptoms, pain, anxiety/and/or depression and sleep problems must be fully addressed if the patient is to be restored to optimal functionality. Patients suspected of having a co-morbid sleep disturbance, e.g. obstructive sleep apnoea and periodic limb movement disorder, should be referred to their G.P’s for further investigation and treatment. Most treatments that effectively reduce pain are correlated with reduced difficulty falling asleep and increased restfulness of sleep. However, it can be difficult to determine whether the sleep improvement is from reduced pain or from sedation induced by the treatment (Menefee et al. Pain Med. 2000;1:156–172). Thus an optimal pain management therapy should relieve pain while also reducing sleep disturbance (Lautenbacher et al. Sleep Med Rev. 2006;10:357-369; Smith and Haythornthwaite. Sleep Med Rev. 2004;8(2):119-32). However, it is important to be aware that some medications focused on treating pain, such as opioids and antidepressants, may disrupt sleep and sleep architecture, further contributing to the pain-sleep disruption cycle (Benca et al. J Clin Psychiatry. 2004;65(8):26-35; Schutte-Rodin et al. Clin Sleep Med. 2008;4(5):487-504; McCrae. Am J Manage Care. 2009;15:S14-S23; Onen et al. Clin J Pain. 2005;21:422–431; Walder et al. Eur J Anaesthesiol. 2001;18(1):36-42) Pain, sleep and mood Pain and sleep disturbance are linked, but in a minority of chronic pain patients, there is also co-existing depression and anxiety—again, both of these are well known as potential causes of disturbed sleep. In a study of chronic pain patients, 65% reported strong or predominant restriction of daily activities, 60% reported strong or predominant sleep disturbance, 34% reported depression, and 25% reported feelings of anxiety (Gustorff B, Dorner T, Likar R et al. (2008) Prevalence of self-reported neuropathic pain and impact on quality of life: a prospective representative survey. Acta Anaesthesiol Scand 52(1):132–136). In another study of patients with chronic pain, higher levels of pain were correlated with increased symptoms of mood and sleep disturbances, as well as decreased mental and physical functioning (Gore M, Brandenburg MA, Dukes E et al. (2005) Pain severity in diabetic peripheral neuropathy is associated with patient functioning, symptom levels of anxiety and depression, and sleep. J Pain Symptom Manage 30:374–385). Pain, sleep disturbance, anxiety and depression are all known to affect daytime function and quality of life. Studies have shown that in chronic pain patients’ subjective aspects of functioning (McCarberg B, Billington R (2006) Consequences of neuropathic pain: quality-of-life issues and associated costs. Am J Manag Care 12(Suppl 9):263–268, Meyer-Rosberg K, Kvarnström A, Kinnman E et al (2001) Peripheral neuropathic pain—a multidimensional burden for patients. Eur J Pain 5:379– 389). Conclusion Chronic pain and its comorbidities disrupt sleep architecture and cause various sleep disturbances, including reduced SE%, increased sleep onset latency, increased awakenings, and non-restorative sleep. The severity of the sleep disruption seen in patients with chronic pain has been similar to that reported for patients with primary insomnia. Simply treating the pain will not necessarily be sufficient to return the patient to optimal functionality. “…. many factors, including pain, disease process per se, as well as medication, could disturb sleep, sleep disturbances may also adversely affect the natural course of the painful disease. Improving sleep quantity and quality in patients with painful disorders may break this vicious circle and as a consequence enhance the patients’ overall health and quality of life.” Onen et al. Clin J Pain 2005;21(5):422-31