5.1  The Relationship Between Pain and Sleep

By Dennis R. Bailey, DDS (USA)

The association between pain and sleep is bidirectional. Having pain may impact sleep quality, and not sleeping well may impact pain levels. The key to understanding this relationship is to understand sleep and to recognize common sleep disorders that impact pain. Unfortunately, for many people with pain, paying attention to sleep quality and recognizing a sleep disorder may not always occur.

Sleep Overview. Sleep is one of the three pillars of life, along with diet and exercise. The amount and quality of sleep is significant when it comes to living a long healthy life. It is important for everyone to understand what constitutes good sleep, what sleep is, and the disorders of sleep that can impact your health as well as your pain.

Under optimum conditions, the amount of sleep an adult should get is between 7 and 9 hours each night, according to the American Academy of Sleep Medicine and the National Sleep Foundation. To achieve your best sleep, your bedtime, and the time you wake each morning should be relatively the same. It is not true that older people require or need less sleep. However, as they age, many people may not get the recommended amount of sleep because of health issues or medications that impact their sleep.

There are two major types of sleep: rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep. One common misconception is that REM sleep is our best or deepest sleep. This is not true. REM sleep is often referred to as dream sleep because this is when we are most likely to experience dreams. NREM sleep is made up of three unique stages based solely on brain-wave activity during these stages (Table 5-1).

Table 5-1. Stages of Sleep
Sleep Type	Amount of Sleep	Characteristics
REM	20–25%	Dream sleep; for memory consolidation
NREM
Stage N1	5%	Transitional sleep stage between REM and NREM stages; lightest stage of sleep
Stage N2	50%	Light stage of sleep
Stage N3	20–25%	Deepest stage of sleep; also known as restorative sleep

Figure 5-1. Stages of sleep during a typical night.

Throughout the night, people go in and out of REM sleep and the different stages of NREM sleep. Typically, as we fall asleep, we transition through NREM stages N1 and N2 into NREM stage N3 and stay there for about 90 minutes. We then enter REM sleep for a brief period and typically go back to NREM stage N3. After another 90 minutes or so, we may go into NREM stage N2, or REM sleep, or both briefly, and then back to NREM stage N3 for a brief period. After approximately 4 hours of sleep, our deepest, restorative sleep is over. We then awaken, albeit briefly; we may or may not be aware of this awakening. For the balance of the night, we typically transition back and forth between REM sleep and NREM stage N2 with a possible awakening and longer REM periods (Figure 5-1).

When we experience sleep disruption, both the amounts of REM and NREM sleep and the stages of sleep may be altered. We may have more awakenings or disturbance in our sleep, referred to as sleep fragmentation, or more REM sleep or NREM stage N2. This occurs because of a variety of conditions, one of which is pain. These disturbances may result in our being tired during the day, having low energy, and having a reduced ability to concentrate. This can lead to other conditions such as anxiety and depression. Most importantly, sleep disturbances have the potential for increasing our pain and impacting our ability to respond to pain.

Two other significant factors are sleep quality (SQ) and sleep efficiency (SE). SQ is one’s subjective perception of how well they slept and is often based on how rested they feel in the morning. In the case of pain, SQ may also be related to the perceived absence or reduction of pain. SE is typically reported as a percentage and is measurable during a sleep study by comparing the hours of sleep, which is determined by brain-wave activity, to the amount of time spent in bed. Having an SE of 85% or higher is the standard norm.

Sleep Disorders and Pain. Sleep and pain share a bidirectional relationship. Sleeping for fewer than the optimal number of hours may result in both increased pain and hyperalgesia, an increased response to painful stimuli. Alternatively, pain may lead to more sleep disturbance, as well as a deficient amount of sleep. Even people who do not suffer from a painful condition can understand the impact of a poor night’s sleep. When a person has a disturbed night’s sleep or a night of inadequate length or quality of sleep, they can feel more tired and less alert, and they may experience pain where pain is not typically present the following day.

Although sleep and pain have a bidirectional relationship, this relationship is not necessarily equal. Studies indicate that presleep pain does not necessarily predict subsequent sleep quality. Additionally, subjective sleep efficiency is the most reliable predictor of pain the next day. However, this applies mostly to pain on waking and for the first half of the day. It may not apply to pain later or in the second half of the day. A classic example of this is facial pain that involves the musculature. Many patients will awaken feeling minimal to no pain but experience an increase in their pain later in the day.

The deprivation of REM sleep leads to increased hyperalgesia the following day. A deprivation of REM sleep may also be associated with frequent disturbances in sleep, known as sleep fragmentation. In addition, REM sleep deprivation has been shown to impact and worsen nociception, that is, the perception or detection of pain.

Achieving a full understanding of how pain and sleep are related requires an understanding of the neurochemicals, also known as neurotransmitters, that transmit signals in the central nervous system and are involved with sleep, wakefulness, and pain. Many of these neurochemicals are interrelated, hence supporting the sleep–pain relationship physiologically.

Common Sleep Disorders That May Impact Pain. There are a wide variety of sleep disorders, some of which occur frequently. Many of these sleep disorders impact sleep quality and duration and, hence, can impact pain. Those with the greatest potential to impact both sleep and pain are as follows:

• Insomnia is the most common sleep disorder. It may be acute, for short periods of time, or chronic and ongoing. Insomnia can involve difficulty getting to sleep (sleep onset) or difficulty staying asleep (sleep maintenance.) Many people experience insomnia when they are stressed, mainly because stress comes with an elevation in cortisol levels, which promotes wakefulness. When pain is present, stress levels may be elevated, leading to more anxiety and thus increased difficulty with sleep.
• Sleep apnoea is often associated with snoring and disruption in breathing during sleep. The most common type of apnoea is obstructive, where the airway is blocked and the person struggles to breath, often observed as gasping during sleep. Sleep apnoea is associated with daytime sleepiness, feelings of tiredness, mood swings, and memory issues. Eighty percent of people with sleep apnoea have not been diagnosed. Of interest is a reciprocal situation. Many times, the bed partner of a person who snores or has apnoea is impacted more than the person with the disorder because their sleep is disturbed; hence, they experience similar symptoms, feeling more pain and having poor sleep quality.
• COMISA stands for comorbid insomnia and sleep apnoea, indicating that these two disorders co-occur. This comorbidity was first identified in 1973, and other studies since then have supported this relationship. Together, these two disorders lead to poor sleep quality and poor sleep efficiency, which potentially impacts pain.
• Movement disorders include restless leg syndrome (RLS), periodic limb movement disorder (PLMD), and sleep bruxism. RLS is typically found in the evening or during sleep initiation and is a clinical diagnosis based on the inability to sit still because of discomfort in the legs. PLMS involves the movement of mainly the legs during sleep and may disrupt sleep. It is diagnosed during a polysomnography, a multiparameter study of sleep that is a diagnostic tool in sleep medicine. Sleep bruxism
• occurs predominately during stage N2 sleep and may disrupt sleep. An increase in N2 sleep is associated with an alteration in other stages of sleep. This disorder may also be associated with various orofacial pain complaints, as well as some types of headaches.
• Narcolepsy is the sudden onset of sleepiness. It may occur at any time and has been associated with an increased amount of daytime sleepiness or hypersomnia. When present, there may be an increased incidence of pain, especially chronic pain. Many times, people with daytime hypersomnolence are thought to have sleep apnoea, so narcolepsy may be overlooked.

Orofacial Pain and Sleep. Orofacial pain encompasses a diverse group of disorders that involve the head, face, and neck, as well as the oral cavity (mouth) and related structures. Orofacial pain involves musculoskeletal, neuropathic, and mechanical disorders, all of which may involve pain and can impact sleep. Temporomandibular disorders (TMDs) are a component of orofacial pain that involve the head and neck musculature, as well as the temporomandibular joints. In one study, patients diagnosed with TMDs had a 36% likelihood of having insomnia and a 28% chance of having sleep apnoea.

Musculoskeletal pain is the most common of all orofacial pain complaints, often referred to as TMDs. Such pain involves the musculature of the head and neck area. Several of the muscles of the head, face, and neck all interact during the day, as well as at night. The muscles of the head and jaw function during chewing, speaking, and swallowing, and some are accessory muscles for respiration. The group of four muscles known as the masticatory muscles are the ones that most often are painful, especially when palpated. In addition, they have the potential to refer pain to distant locations. This was described several decades ago by Travel and Simons. What they described were areas in a muscle, termed trigger points, that, when provoked, would be felt as pain in another location. This is known as referred pain. As an example, pain in a muscle that moves the jaw may refer to a tooth or multiple teeth. These same muscles may refer to other areas such as over the eyes, the forehead, or the face and are potentially thought to reflect a headache or sinus problem. Travel and Simons mapped these trigger points, as well as the typical areas where the pain was felt (Figure 5-2).

Figure 5-2. Based on the work of Travell and Simons, mapped trigger points (black X’s) show possible areas (red) where pain may be felt: (A) masseter muscle and (B) temporalis muscle. Images courtesy of Dr. Rich Hirschinger, DDS, MBA, inventor of the gentle jaw.

The muscles of the neck are also important, as they help with posture and may also be involved as accessory muscles for respiration. The posture of the head is important and, when not correct, can also lead to pain that is experienced in a distant location, such as the face or jaw. The key factors that may impact head posture are previous trauma, such as a motor vehicle accident, working at a desk or computer with poor posture, or an airway that is compromised or restricted. Poor posture and head and neck support during sleep may precipitate pain that is experienced in the head, jaw, or face. The main nerve to the face and jaw, the trigeminal nerve, interacts with nerves from the cervical spine and is perceived as pain by the brain.
Neuropathic pain, and in particular trigeminal neuralgia (TN), is of particular interest in relation to sleep. Historically, TN was thought to be silent during sleep, indicating some type of protective mechanism so that it did not awaken the person. In 2008, however, it was found that this was not the case. Individuals with TN and their bed partners reported that awakenings were in fact present and common. Based on this finding and our understanding of how pain and sleep interact, it is evident that the disruption in sleep associated with TN may lead to symptoms of fatigue, including chronic tiredness and low energy during the day. There is a 20% chance that an individual with TN or neuropathy will have more awakenings during sleep or have poor-quality sleep.
Management of Orofacial Pain and Sleep. Managing any sleep disorder has the potential to impact pain positively. Therapies that may be most helpful include the following:

• Cognitive behavioral therapy (CBT) provides a series of lessons on how to calm the mind, relax, and improve sleep. Part of this therapy is termed sleep hygiene and is designed to eliminate distractions from the bedroom, thereby improving sleep onset, quality, and efficiency. CBT is offered by psychologists, and recently, online programs have become available. This program helps mainly with insomnia and is beneficial for pain management. Recently, an online prescription therapeutic program for chronic insomnia that is approved by the Food and Drug Administration (called Somryst) was acquired by Nox Health and should be available soon.
• Mindfulness is a form of meditation that can involve breathing exercises and guided imagery. The goal is to be able to achieve a feeling of relaxation in, and not overreact to, any situation.
• Focusing on nasal breathing as opposed to mouth breathing can be extremely helpful. Breathing through the nose increases oxygen uptake and improves oxygen levels in the bloodstream. There are aids to improve nasal breathing, called nasal dilators, that can be used at night. Aids to help prevent mouth breathing are available as well.
• If obstructive sleep apnoea is suspected, consult a physician. The most common therapy is using a continuous positive airway pressure (CPAP) device. However, oral appliances are an option if the apnoea is mild or moderate or if the issue is just snoring. An oral appliance moves the lower jaw forward and helps open and stabilize the airway, preventing the tongue from collapsing into the airway during sleep. These appliances may also address sleep bruxism, and this can lead to better pain control.
• Paying attention to a good diet and adequate exercise will help improve sleep and thus help manage the pain. Both diet and exercise are also important aspects of improved health.
• If medication has been prescribed for a sleep issue, seek an alternate means of addressing the sleep issue. For example, if medication has been prescribed to treat insomnia, use the medication for insomnia, but pursue CBT as well, as this may help reduce or eliminate the need for medication. Many medications have a negative impact on sleep. An exception is narcolepsy, for which medication is needed to address the physiologic cause.
• Seek help from an orofacial pain specialist. Recently, orofacial pain became a dental specialty. Dentists who have extensive training in this discipline are well versed in the management of orofacial pain conditions and can play a major role in helping people manage their pain. Orofacial pain specialists typically work in concert with all types of physicians, physical therapists, psychologists, and other health care providers to achieve an optimum outcome. Specialists in orofacial pain are also trained in sleep medicine, from both the diagnostic side and the management side. Most belong to the American Academy of Orofacial Pain.

Conclusion. The association between sleep dysfunction and pain is well documented. It has been reported that poor sleep is present in 50% to 80% of people with chronic pain. However, the management of pain and sleep together may not always occur. In many cases, it may be necessary to prioritize either sleep or pain to adequately address the other. Regardless, paying attention to both will no doubt impact the priority issue as well. It is imperative that the sleep–pain bidirectional relationship be a consideration, so that optimum outcomes are the result. This will ultimately lead to more effective pain management and an improved quality of life.