Sleep and Chronic Pain



Fig. 16.1
Sleep stages and function



The amount of sleep required varies between individuals, and the amount of sleep obtained is influenced by age, environmental demands, and many other biological, psychological, and social factors. There is no clear consensus what constitutes “normal” sleep, but conventionally, sleep is considered disturbed if it is characterized by a long sleep onset latency (SOL; ≥30 min), long duration of awakening after sleep onset (WASO; ≥30 min), short total sleep time (TST; ≤6.5 h), low-quality/nonrefreshing sleep, or a sleep efficiency (SE; the proportion of time in bed asleep) of 85 % or below (Table 16.1).


Table 16.1
Abbreviations of sleep architecture




































Sleep architecture

NREM

Non-rapid-eye-movement sleep composed of four distinct stages: N1 and N2 are characterized by lighter sleep, while N3 and N4 are regarded as deeper stages of sleep

REM

Rapid-eye-movement sleep follows stage N4 sleep, and dreams usually occur during this period. This phase is characterized by rapid, shallow breathing, raised heart rate and blood pressure, jerky eye movement, and brain wave patterns similar to wakefulness. Also known as paradoxical sleep

SWS

Slow wave sleep: stages N3 and N4 of NREM; N4 consists almost entirely of SWS

SOL

Sleep onset latency: time taken to fall asleep

WASO

Wake after sleep onset: time awake following initial onset of sleep

TWT

Total wake time: cumulative amount of time awake

TST

Total sleep time: cumulative amount of time sleeping

SE

Sleep efficiency expressed as a percentage of time in bed asleep: (total sleep time/total time in bed)  ×  100 %

SQ

Sleep quality: a subjective rating of quality of sleep




Scientific Relevance to Pain Care



Prevalence and Pattern of Sleep Disruption in Chronic Pain


Complaints of sleep disturbance have been documented in a variety of individuals reporting pain symptoms. A large-scale community-based survey investigating the prevalence of sleeping difficulties in multiple European countries found that 23.3 % of participants who reported experiencing pain also reported difficulties sleeping, while only 7.4 % of participants reporting impaired sleep were without pain [36]. In a prospective postal survey of adults in the UK, pain reported at baseline was a significant risk factor for developing insomnia symptoms 1 year later [37]. These findings are consistent with those obtained from the Sleep in America Survey conducted in 2003, indicating that the presence of bodily pain increased the odds of insomnia by approximately twofold in older adults [38].

Sleep disturbance is a common consequence of acute pain; estimates of sleep disturbance experienced during hospitalization postsurgery range between 22 and 61 % [3941]. In these patients, polysomnography (PSG; an instrument to measure sleep) has indicated frequent awakenings, shorter TST and SE, as well as more frequent transitions between the sleep stages with longer duration of N1 sleep, and reduced SWS and REM sleep [40, 42]. This disturbance is generally short-term, and TST returns to preoperative levels within 1 week of hospitalization for the majority of patients [3941]. Similarly, nighttime pain in patients hospitalized for burn injuries is associated with frequent awakenings and reduced sleep quality and TST. Sleep disturbance was reported by 75 % of patients on at least one night during the 5-day study period [43].

Sleep disturbance is also a common problem in cancer and a number of chronic pain conditions, such as RA, osteoarthritis (OA), FM, headache, and musculoskeletal pain conditions. In a review of cancer-related insomnia, the prevalence of sleep disturbance in this population was estimated between 30 and 50 % post-diagnosis [44]. The insomnia rate only dropped slightly (estimated between 24 and 44 %) when assessed 2–5 years after treatment [44] suggesting insomnia itself is a chronic problem for this population, although cancer pain specifically increases difficulties initiating sleep and frequent awakenings [45].

Confining the focus to chronic noncancer pain, as many as 90 % of the patients attending tertiary pain clinics have complaints with their sleep [7, 8, 11, 46, 47], and approximately 53 % of these patients have insomnia of a severity that warrants clinical attention [9]. Apparently, the pattern of sleep disturbance in these chronic pain patients is largely comparable to that of patients with primary insomnia [48]. Common problems cited by chronic pain patients are initiating sleep and frequent awakenings [7, 8]. Studies using PSG have indicated that chronic pain patients have more microarousals, more body movements during sleep, more frequent transitions between the sleep stages with increased N1 and N2 sleep and reduced N3 and N4, frequent awakenings, and lower SE, compared to healthy volunteers [49, 50]. Sleep disruption experienced by these patients is also characterized by reduced spindle activity at N2 sleep [51], an increase in the rate of cyclic alternating pattern (CAP); [52] a lack of heart rate variability reduction [53] and an intrusion of electroencephalographic (EEG) activity in the alpha range (8–13 cps) during NREM sleep [54]. Although alpha-delta sleep was once thought to be a signature of pain-related sleep disturbance [55], there is now conflicting evidence suggesting otherwise [5659]. It remains open as to whether or not there is a neuro-physiological marker of sleep complaints exclusive to the pain population.


Primary Sleep Disorders Other than Insomnia in Chronic Pain


Sleep disorders other than insomnia, including periodic limb movement (PLMD) and sleep apnea, have a heightened prevalence among patients with chronic pain [60, 61]. PLMD and restless leg syndrome (RLS) are closely related movement disorders that often disturb sleep onset and maintenance. PLMD occurs during sleep with spontaneous movement of the lower extremities. RLS occurs during the day or night and is associated with an unpleasant sensation in the lower extremities somewhat relieved with movement. There is always a strong urge to move with RLS, and it can be the genesis of movement and pain at night. Approximately 80 % of patients with RLS have PLMD [62]. The etiology of PLMD and RLS is not well understood, but some forms appear to be due to a dopaminergic dysfunction. Secondary PLMD and RLS have been associated with iron deficiency, folate deficiency, chronic renal failure, OA, and small-sensory-fiber disease [63]. Pain from OA and dysesthesias from small sensory nerve disease are factors that contribute to sleep disturbances with patients who have PLMD and RLS [64].

Chronic headaches appear to be strongly associated with obstructive sleep apnea (OSA); OSA sufferers are seven times more likely to experience chronic headaches (defined as occurring 15 or more times per month) than people in the general population [65]. The severity of the headaches, which tend to occur in the morning, is directly related to the severity of OSA [66]. A strong association also appears to exist between FM and sleep apnea. The prevalence of FM in a study of 50 patients with sleep apnea was tenfold higher than in the general population [67]. Patients with FM often experience OSA [60], and it is possible that OSA plays an etiologic role in some cases of FM. In one case study, a woman with FM and OSA saw great improvement of her FM symptoms after being treated for OSA with nasal continuous positive airway pressure (CPAP) [68]. However, the current research on the link between primary sleep disorders and chronic pain is thin; the rate and variety of comorbid sleep disorders may have been underdetected and/or underreported.


Sleep-Pain Interaction


We have seen that disturbed sleep and chronic pain frequently go together and that the relationship is often assumed to be bidirectional. There are studies showing that the introduction of nociceptive stimuli during sleep can produce cortical arousal [6971] and that deprivation of sleep – in particular, REM sleep and SWS – can heighten pain intensity [7274]. However, as more experimental data accrue, the relationship between sleep and pain emerges to be more complex than originally thought.

On the effect of sleep disturbance on pain, there are confusing findings regarding the relative importance of REM sleep and SWS disruption in pain responses. For example, in one study of healthy pain-free sleepers, the loss of 4 h of sleep associated with REM sleep disruption had a greater hyperalgesic effect than the loss of an equal amount of sleep that was associated with NREM sleep interruption [75]. In another study [72], recovery sleep following SWS interruption, but not REM interruption, increased pain thresholds. Contrary to the previous study [75], this finding suggests that SWS plays a more important role than REM sleep in determining the pain tolerance levels. Further, in an elegant study designed to tease apart the effect of sleep deprivation from sleep fragmentation, healthy controls who were in the sleep fragmentation condition demonstrated a significant loss of pain inhibition and an increase in spontaneous pain, while sleep deprivation did not produce any effect on pain thresholds. This interesting finding indicates that the lack of sleep continuity, rather than simple sleep restriction, impairs endogenous pain-inhibitory function and increases spontaneous pain [76].

Pain is frequently cited by patients as the cause of their sleep disturbance [8], and consistently, pain intensity ratings have been found to predict sleep disturbance [47, 77]. However, not all studies identify a significant relationship between pain severity and sleep [78], and certainly not every pain patient has problems sleeping. A subset of individuals with high pain intensity manage to have normal sleep or even regard themselves as “good sleepers” [7, 9, 47, 78]. Although there are clinical studies noting pain to be predictive of subsequent poor sleep, the amount of within-subject variance in sleep explained by pain was rather small and often became nonsignificant when other psychological variables (e.g., pain attention, presleep cognitive arousal) were statistically controlled for [79, 80]. In fact, evidence is accruing to suggest that cognitive behavioral factors common in primary insomnia (such as rumination, worry, health- and sleep-related anxiety, poor stimulus control, pre-sleep arousal, and dysfunctional sleep beliefs) may be better predictors of insomnia severity than pain intensity per se [9, 81, 82, 151].


Clinical Practice



Sleep Assessment


When a pain patient is complaining of insomnia, there are various ways to assess the complaint, such that both the subjective distress of the complaint and the objective characteristics of the sleep disturbance are captured. Although there are sophisticated tests and equipment available for the measurement of sleep, most cases of insomnia are primarily diagnosed by clinical evaluation.

A detailed clinical interview should include a careful evaluation of the patient’s sleep history, medical and psychiatric history, current and past use of substances, and history of treatment for the sleep problem. When asking the patient about the sleep history, it is important to gather information about the (1) typical sleep-wake schedule; (2) past diagnosis of and treatment for sleep/psychiatric disorder(s); (3) nature and onset of the current sleep complaint; (4) frequency, severity, and duration of the sleep problem; and (5) whether or not the sleep problem has daytime consequences or is causing significant distress. This should provide information to establish if the patient meets the basic diagnostic criteria for insomnia – the three most commonly used classification systems are DSM-IV-TR [83], ICD-10 [84], and ICSD-2 [85]. Moreover, it would be helpful for the clinician to ask questions about the following: the patient’s occupation (e.g., doing shift work or jobs requiring frequent long haul travel), general lifestyle (e.g., leading a sedentary lifestyle; napping often; consuming excessive alcohol, drugs, caffeine, and/or other stimulants), current and past life stresses that could cause anxiety and depression (e.g., pain, bereavement, divorce, job loss), bedroom environment (e.g., too hot/cold/ bright/noisy, having a bed partner who snores), general beliefs about sleep (e.g., “I must have 8 h of sleep a night!”), sleep practices (e.g., having a pre-sleep wind-down routine; if woken up, staying in bed for hours to try and go back to sleep), and their typical response to a poor night’s sleep (e.g., feeling annoyed and frustrated; worried about losing control over sleep; cutting daytime appointments for fear of not being able to function well; going to bed early to catch up on sleep, even when not sleepy). This should help establish the psychophysiological factors precipitating and perpetuating the sleep problems. There are structured interview schedules available to guide and assist the assessment of insomnia and sleep disorders. Examples of these include the structured interview for sleep disorders according to DSM-III-R [86] and the Duke Structured Interview Schedule for the diagnoses of DSM-IV-TR and International Classification of Sleep Disorder, second edition (ICSD-2) [87]. The use of these instruments, however, requires training and practice.

While a thorough clinical interview should form the core of the evaluation, a combination of self-report questionnaires and a sleep diary (with or without actigraphy) can be used to aid the assessment. Self-report questionnaires such as the Insomnia Severity Index [88], the Pittsburgh Sleep Quality Index (PSQI) [89], the Mini-Sleep Questionnaire [90], the Uppsala Sleep Inventory [91], the Medical Outcome Study Sleep Questionnaire [92], and the Dysfunctional Beliefs and Attitudes About Sleep Scale [93, 94] have been used to assess sleep difficulties in chronic pain conditions. However, it must be emphasized that most of these questionnaires are designed to measure sleep quality rather than for diagnostic purposes. As such, their scores should be interpreted with caution as they are neither sufficient to establish a differential diagnosis nor to guide the planning of treatment. Moreover, retrospective responses to these sleep questionnaires are often obscured by recall bias and mood state of the individual at the time of assessment [95].

It is good practice to prescribe 2 weeks of sleep diaries to obtain a more stable picture of the sleep pattern [10]. Each diary entry is essentially a short questionnaire to be completed immediately after waking to provide information concerning the previous night for sleep onset latency (SOL), frequency and total duration of wake time after sleep onset (WASO), total sleep time (TST), and sleep efficiency (SE). Depending on the nature of the sleep complaint, sleep diaries may also include reports of sleep quality (SQ), pain, use of medication and substances, daytime sleepiness, and fatigue to provide additional information for assessment and case formulation. Although sleep diaries are generally easy to use and there have been clinical reports suggesting therapeutic benefits associated with regular sleep monitoring, care must be taken to explain to the patient the rationale and procedure of the sleep monitoring so as to enhance adherence.

If appropriate, the use of a sleep diary can be complemented by the use of an actigraph (also known as an accelerometer), which is a wristwatch-like device to be worn on the nondominant wrist to measure and record the intensity and duration of physical motion. The rationale behind the use of this technology in sleep research is that frequent and intense movement during the night is indicative of wakefulness. With the aid of an algorithm, data extracted from the actigraph can be used to provide objective estimates of basic sleep parameters, such as SOL, WASO, and TST. The actigraphic measurements of TST, WASO, and SE compare well (r  =  0.49–0.98) with corresponding sleep parameters recorded by polysomnography [96]. Actigraphy has shown modest agreement (r  =  0.34–0.44) when compared with subjective reports of sleep given by people with musculoskeletal pain [77]. Actigraphy has also demonstrated a high degree of stability across nights (r  =  0.4–0.81) [77, 97]. A strong relationship (r  =  0.64) has also been observed between the actigraph measure of TST and the perceived sleep quality reported by women with FM [98]. However, it should be noted that actigraphy is recommended to establish the sleep-wake pattern over time rather than to generate estimates of sleep parameters as this technology may underestimate SOL and overestimate TST in individuals who manage to lie still over long periods. Kushida et al. [99] recommend that sleep diaries and actigraphy should be used simultaneously to provide more detailed information regarding sleep.

Although polysomnography (PSG) is considered the gold standard of sleep measurement [10, 99], it is not recommended for routine sleep assessment. PSG can provide information about the architecture of sleep (see “Sleep Architecture”) via three measures: electroencephalography (EEG: measurement of brain waves/electrical activity), electrooculography (EOG: measurement of eye movement), and electromyography (EMG: measurement of facial muscle tension) [100]. Coupled with other electrophysiological measures (e.g., EKG, electrocardiograms, nasal/oral air flow, oxygen desaturation, leg movement), the clinician could extract useful information for the diagnosis of sleep disorders such as sleep apnea, PLMD, and RLS (which are described in “Primary Sleep Disorders Other than Insomnia in Chronic Pain”). However, the use of PSG can be intrusive to the patient’s sleep, expensive to conduct, and laborious for the clinician to set up and score the results. These limitations are some of the reasons why PSG is often less accessible to the general public and the duration of sleep study is usually restricted to a short period of time (less than three nights). PSG is not indicated unless the pain patient is suspected of having primary sleep disorders. A sleep study is recommended, however, when a patient is on high-dose opioids (>150 mg), considering the strong association between daily opioid dosage and sleep apnea [101]. A home study is less expensive than in-lab PSGs and, in most cases, is sufficient to diagnose sleep-disordered breathing and to differentiate central sleep apnea from OSA. Patients with sleep apnea must be treated accordingly or have their daily opioid dose decreased, after which a repeat sleep study is recommended.


Managing Sleep Disturbance in Patients with Chronic Pain


Sleep disturbance co-occurring with chronic pain can be managed using pharmacotherapy and/or psychological therapy. The sections below describe these treatment approaches, and Table 16.2 provides a summary of their respective mechanisms, advantages, and disadvantages with a view to informing clinical decisions (Table 16.2).


Table 16.2
Mechanisms, advantages, and disadvantages of the mainstream pharmacological agents and psychological treatments for chronic pain patients with concomitant insomnia

































































































Treatment

Mechanism

Advantages

Disadvantages

Analgesics (e.g., NSAIDs, opioids)

NSAIDs reduce inflammation and algesia by inhibiting arachidonic acid but have no sedative effect. Inhibition of prostaglandin biosynthesis is through inhibition of COX-1 and COX-2 enzymes. COX-1 activation leads to production of prostacyclin which is cytoprotective. COX-2 is induced in inflammatory cells. The ratio of COX-1 to COX-2 determines the likelihood of adverse effects. Opioids bind to mu, delta, and kappa receptors; effect is to decrease presynaptic calcium flux, which decreases neurotransmitter release. Opioids also increase postsynaptic K+ flux, resulting in hyperpolarization of the neuron, decreasing conductance and transmission. The analgesic and sedative effects of opioids arise from the inhibition of cholinergic, adenosinergic, and GABAergic transmission

The analgesic effects of NSAIDs may reduce nighttime arousal

Analgesics may increase awakening and alter sleep architecture, suppressing SWS and REM sleep

The sedative effects of opioids hasten sleep onset.

Other side effects include nausea, vomiting, diarrhea, constipation, skin complaints, dry mouth, dizziness, headaches, blurred vision, and fluid retention. The more severe complications are stomach ulcers and kidney/liver failure

There is also the risk of addiction with prolonged use of opioids [102]

Anticonvulsants (e.g., gabapentin, pregabalin)

Mechanism is not known but appears to involve activation of the alpha2-delta protein subunit, which decreases Ca+ flux and slows depolarization of neuronal activity of postsynaptic neurons.

Demonstrated efficacy in improving pain and functional measures, including sleep [103]

Pain relief happens when optimal dose is achieved. Optimal doses of these drugs vary from individual to individual; careful monitoring and patient titration are required

Increase SWS without detrimenting REM sleep [104]

Some patients cannot tolerate these drugs well, particularly those who are on high doses, causing premature drug withdrawals

Effective in the treatment of RLS and PLMD [105]

Common adverse effects include dizziness, peripheral edema, somnolence, confusion, headache, dry mouth, and constipation

Pregabalin is thought to be less of a risk for dependence/abuse than other classes of medication [106]

Tricyclic antidepressants (e.g., amitriptyline, nortriptyline)

Inhibit neuronal uptake of norepinephrine and serotonin into the presynaptic nerve terminals by inhibiting the serotonin and norepinephrine transporters at an approximately 1:8 ratio. They also block postsynaptic sodium, calcium, and potassium channels

Some evidence of pain relief

Off-label use only; none of the TCAs has been approved by the FDA for treatment of DPNP or any type of pain

Hasten sleep onset

TCAs alter sleep architecture.

Beneficial for pain patients with concomitant mood problems

Possible side effects include daytime drowsiness, dry mouth, blurred vision, constipation, urinary retention, and heart conditions

TCAs may increase the risk of suicide attempt [107, 108]

Amitriptyline is a relative contraindication for older patients and patients with any cardiovascular disease [109]

Selective reuptake inhibitors (e.g., duloxetine, venlafaxine, milnacipran, desvenlafaxine)

Prevent serotonin and norepinephrine form being reabsorbed into the presynaptic terminals. Duloxetine differs from venlafaxine in that it is comparatively more noradrenergic. Venlafaxine has a 30-fold higher affinity for serotonin than for norepinephrine, while duloxetine has a tenfold selectivity for serotonin [110]. Approximate potency ratios (5-HT:NE) are 1:10 for duloxetine and 1:30 for venlafaxine

Lack most of the side effects of tricyclic antidepressants and monoamine oxidase inhibitors

Nausea is the most common side effect for most drugs in this class

Duloxetine is approved for the management of neuropathic pain associated with diabetic peripheral neuropathy and FM

This class of drug is also associated with increased blood pressure and insomnia [110112]

Cytochrome P450 isoenzymes inducers and inhibitors can affect drug levels

Hypnotics (e.g., clonazepam, zolpidem)

Facilitate GABAergic transmission. BZDs and other hypnotics (non-BZDs) bind to the gamma subunit of the GABA-A receptor, which increases chloride ion conductance and inhibition of the action potentials

Established efficacy for both BZDs and non-BZDs for acute and short-term management

Potential side effects include daytime drowsiness, dizziness, impaired memory, concentration, and psychomotor performance

Fast-acting

There is the risk of tolerance and dependence with extended use, and rebound insomnia may occur after discontinuation [113]

Pain management programs (multidisciplinary programs in the US)

Treatment delivered by multidisciplinary team. Program content varies but generally includes psychoeducation on pain, relaxation techniques, physical exercises, CT for pain, and behavioral pain and stress management strategies; many programs also offer sleep hygiene education

Moderate treatment effects have been achieved for improved coping and self-efficacy regarding pain [114]

Treatment effects are generally small for reducing pain severity [114]

The group format encourages social support and facilitates behavioral change [115]

Focus of treatment is largely on rehabilitation. Not enough individual therapy time for complex cases that present with other comorbid anxiety, mood, and sleep problems
 
Limited coverage on sleep; only minimal improvements on sleep are detected in graduates of PMPs [116]

Remission rates in a range of pain and functional outcome measures are between 18 and 33 %, with 1–2 % of the patients reliably deteriorate during the period of treatment [117]

CBT for insomnia

Treatment delivered both individually or in groups by trained psychologists or behavioral sleep medicine specialists. Content varies but generally include psychoeducation on sleep, sleep hygiene, relaxation training, CT for sleep, sleep restriction, stimulus control, paradoxical intention, biofeedback, and imagery training

Highly efficacious and cost-effective; recommended for chronic insomnia [118]

Improved sleep does not necessarily bring about a reduction in pain [119121]

Durable treatment has been achieved in core sleep parameters when CBT-I is directly applied to treat pain-related insomnia [119, 120]

Remission rates in individuals with pain-related insomnia are between 16 and 57 % [119121]

Further refinement is required to address sleep-interfering processes specific to chronic pain patients [48]

The initial stage of CBT-I involves cutting down time resting in bed and the introduction of mild sleep deprivation. This may aggravate pain/discomfort for some individuals

The use of sleep restriction therapy involves getting out of bed and going to another room when woken from sleep. This may be difficult for patients who have restricted mobility


NSAIDs nonsteroidal anti-inflammatory drugs, COX cyclooxygenase enzyme, K+ potassium cation, GABA gamma aminobutyric acid, SWS slow wave sleep, REM rapid eye movement, Ca+ calcium cation, RLS restless leg syndrome, PLMD periodic limb movement disorder, TCAs tricyclic antidepressants, FDA food and drug administration, DPNP diabetic peripheral neuropathic pain, BZDs benzodiazepines, CT cognitive therapy, PMPs pain management programs, CBT-I cognitive behavioral therapy for insomnia


Pharmacological Treatment


A number of pharmacological treatments are available for patients’ sleep disturbances and pain; however, adverse effects are frequent, and patients should be monitored closely for medication-related effects on sleep pathology and pain sensitivity. Pharmacologic treatment options to manage pain include nonsteroidal anti-inflammatory drugs, opioids (morphine, oxycodone, methadone, codeine, fentanyl, buprenorphine, hydromorphone, dextropropoxyphene, and pentazocine), tricyclic antidepressants (amitriptyline), and selective norepinephrine reuptake inhibitors (duloxetine). Options to manage sleep disturbances include hypnotics and related drugs, such as benzodiazepines (BZDs-clonazepam) and nonbenzodiazepines (zolpidem, zaleplon, and eszopiclone) [122, 123]. Patients treated with opioids and BZDs should be cautioned not to take more medication than directed, even if pain is uncontrolled, because unauthorized escalation of doses could be lethal. Opioids and BZD doses should be reduced by approximately 20 % if the patient develops a flu or severe respiratory infection. For nocturnal pain, off-label use of anticonvulsants and antidepressants is less likely than opioids to depress respiration.

Some pharmacologic treatments can impact sleep architecture, sleep restoration, and pain threshold levels. Morphine, for example, has reduced SWS (by 75 %) and REM sleep, while increasing N2 sleep, [124] and in a separate study, morphine and methadone increased N2 sleep and significantly decreased N3 and N4 sleep (p  <  0.001) [125]. In contrast, patients with chronic pain from OA showed significantly lower pain scores from baseline following morphine sulfate as well as increases in TST and SE [126]. Some newer anticonvulsants have been found to have negligible impacts on sleep architecture, and some may even improve it. For instance, gabapentin and pregabalin were found to promote modest increases in SWS without affecting REM sleep in healthy adults [103, 104, 127, 128].

Additional adverse effects must be considered when treating patients pharmacologically. For example, opioids, particularly methadone, have been associated with a high rate (75 %) of sleep-disordered breathing in patients with chronic pain [129]. Concomitant BZD administration was shown to have a significant additive effect on methadone-related central sleep apnea. In another study, the prevalence of central sleep apnea was found to be 30 % in patients undergoing methadone maintenance treatment [130].

Methadone is not the only opioid associated with alarming levels of sleep apnea. There appears to be a dose relationship of all opioids to central sleep apnea. A linear relationship of opioid dose to central sleep apnea has been reported with immediate release and sustained release formulations. Doses of 150 mg morphine equivalence have approximately a 70 % probability of central sleep apnea [101]. Hypoxia due to hypoventilation has also been observed in patients on chronic opioid therapy even without evidence of sleep apnea (Lynn Webster, personal communication).

Tricyclic antidepressants (TCAs), commonly administered for neuropathic pain, concurrently address symptoms of insomnia and depression. A meta-analysis of 61 clinical trials found that TCAs have demonstrated effectiveness for treatment of diabetic neuralgia and postherpetic neuralgia and to some extent for central pain, atypical facial pain, and postoperative pain after breast cancer treatments [131]. Possible adverse effects of TCAs include drowsiness, dry mouth, blurred vision, constipation, urinary retention, and more serious heart-related conditions [131]. Tricyclic antidepressants have been linked to increased risk of suicide attempts [107, 108] and may reduce seizure thresholds in vulnerable individuals [132]. The newer SNRI formulations (e.g., duloxetine, milnacipran, desvenlafaxine) are reported to have much fewer side effects and increased tolerability. This is particularly important to elderly patients who tend to be more sensitive to the side effect profile of many medications.

Benzodiazepines (BZDs) are frequently used to treat sleep disorders, but their efficacy for sleep disturbances complicated by pain is unclear, and more research is needed. Some studies show improved sleep outcomes, including decreased SOL and WASO and increased TST; however, many other studies demonstrate either no effect or heightened levels of pain compared to controls [123]. It should be noted that prolonged use of BZDs has been associated with increased risk of hip fractures in the elderly [133], although some research shows that prior risk factors such as depression and antidepressant use often precede a new BZD prescription in older adults [134]. It appears that newer BZDs and the non-BZDs may offer enhanced safety and greater efficacy as related to sleep outcomes, but data are limited with relation to pain management [123, 135].


Nonpharmacological Treatment


Although pharmacological management of insomnia is commonly used as the first-line treatment for pain-related sleep disturbance, clinical experience tells us that many patients prefer not to have another tablet for sleep, not only because of the adverse effects mentioned above but also for fears of potential drug interaction, tolerance, and dependence. While pharmacotherapy can have a favorable risk-benefit profile in many individuals, evidence in support of its efficacy and safety beyond 6–12 months is currently thin [113]. Long-term hypnotic medication is usually not indicated for the type of insomnia experienced by chronic pain patients, which often is as chronic as the pain itself and requires a different approach of management.

While most cases of insomnia in chronic pain were precipitated by the onset of pain, the relative importance of pain as a maintaining factor decreases as the insomnia persists. Factors perpetuating the insomnia proliferate as the patient develops compensatory strategies to cope with the pain (e.g., resting in pain, inactivity, ruminating about the pain) and the sleep loss (e.g., extending bedtime, daytime naps, drinking large amounts of tea and coffee to stay alert during the day). Similar to what is happening in primary insomnia, these perpetuating factors tend to be cognitive behavioral in nature and are often amenable to psychological treatments grounded on the cognitive behavioral principles. Multidisciplinary pain programs, which are sometimes called pain management programs (PMP), and cognitive behavioral therapy for primary insomnia (CBT-I) are obvious alternatives to pharmacological treatments. These two forms of treatment will be reviewed in this section with a particular focus on their effectiveness for pain-related insomnia.

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Oct 21, 2016 | Posted by in PAIN MEDICINE | Comments Off on Sleep and Chronic Pain

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