Fibromyalgia and Sleep

Chronic pain in fibromyalgia patients, together with its associated symptoms and co-morbidities, is now considered a result of dysregulated mechanisms in the central nervous system (CNS).

As fibromyalgia patients often report sleep problems, the physiological processes that normally regulate sleep may be disturbed and overlap with other CNS dysfunctions. Although the mechanisms potentially linking chronic widespread pain, sleep alterations and mood disorders have not yet been proven, polysomnography findings in patients with fibromyalgia and non-restorative sleep and their relationships with clinical symptoms support the hypothesis of a conceptual common mechanism called ‘central sensitisation’.

Food and Drug Administration (FDA)-approved drugs for the treatment of fibromyalgia may benefit sleep, but their label does not include the treatment of fibromyalgia-associated sleep disorders. Non-pharmacological therapies (including a thorough sleep assessment) can be considered in the first-line treatment of non-restorative sleep, although they have not yet been fully investigated in patients with fibromyalgia. Both pharmacological and non-pharmacological treatments should be used cautiously in patients with fibromyalgia, bearing in mind the patients’ underlying disorders and the potential interactions of the therapies.

Chronic widespread pain (CWP) is the leading symptom of fibromyalgia (FM). For many years, researchers attempted to identify structural pathology in peripheral tissues and muscles, but then had to admit the lack of any definite evidence of peripheral damage or inflammation.

More progress in understanding FM and its related syndromes was made when investigators turned their attention to the role played by the nervous system .

As a large percentage of FM patients report sleep disturbances, including difficulties in falling or staying asleep, early morning awakenings and non-restorative sleep (NRS) , some researchers soon concentrated on dysfunctions in the sleeping/waking brain. They were particularly interested in their contribution to CWP, unrefreshing sleep, fatigue, impaired quality of life and psychological disturbances of FM patients .

Consciousness is required to translate sensory afferent input into pain as a physiological and emotional experience. While sleeping, the brain does not discriminate pain from other sensory information but is aware of, and reacts to threatening stimuli . Sleep unconsciousness prevents awakenings due to irrelevant sensory inputs. ‘Arousals’ are intermittent and transient increases in autonomic brain activity in response to an afferent input that activates a low-intensity, physiological fight-or-flight response. These arousals can remain unconscious or lead to vocal or motor reactions as a fully awakened response. A descending system directed towards the limbs or the heart, or ascending systems projecting into the cortex , can activate protective fight-or-flight systems, thus potentially inducing a low- or high-intensity fight-or-flight wake reaction.

Research into disturbed sleep in patients with chronic pain (particularly in those suffering from FM) overlapped with the concept of NRS. The restorative theory considers brain activity during sleep essential to restore the functioning of the body and mind . The fatigue and feelings of daytime tiredness that are often associated with NRS can be due to abnormal sleep restoration, particularly when they cannot be explained by insufficient sleep duration. As NRS is common in patients with organic sleep disorders, it has been considered a symptom of insomnia. Many studies have investigated the symptoms of insomnia associated with chronic pain syndromes, particularly FM, and chronic fatigue syndrome (CFS), but studies of NRS are rare and, as greater knowledge of NRS and its mechanisms could provide important insights into the causes of FM and related conditions, more are certainly warranted.

Definitions

The exact mechanisms of the relationship between sleep and health are still a subject of research, but it is generally agreed that sleep is regulated by a complex network of physiological processes and substantially contributes to multiple physiological functions, including cardiovascular, endocrine, immunological, psychiatric and neurological functions . Consequently, poor sleep quality or quantity increases the risk of medical and psychiatric diseases .

The current method of assessing physiological sleep parameters is based on polysomnography (PSG), which records muscle tone by means of an electromyography (EMG), eye movements by means of an electrooculography, and brain activity by means of electroencephalography (EEG) . The two main states of sleep are rapid eye movement (REM) sleep, which is believed to be due to the processing of cognitive stimuli encountered when awake and for memory consolidation , and non-REM sleep, which the American Academy of Sleep Medicine classification currently divides into three stages (N1, N2 and N3), although there were previously the following four : stage W (wakefulness), during which the predominant EEG findings are alpha waves with a frequency of 8–12 Hz; stage N1 (light sleep, normally <5% of total sleep time), during which the main EEG findings are theta waves with a frequency of 4–7 Hz (this first stage of true sleep is characterised by slow and regular eye movements); stage N2 (intermediate sleep, 40–50% of total sleep time), deeper sleep characterised by EEG findings of sleep spindles and K-complexes, with no slow and regular eye movements; and stage N3 (deep or slow-wave sleep, 20% of total sleep time), characterised by EEG findings of slow delta waves with a frequency of 0.5–2 Hz. During the first half of sleep, individuals cycle between REM and all stages of non-REM sleep; during the second half, the cycling is between stage N2 and REM sleep. Each cycle normally lasts 1–2 h, whereas stage N1 typically lasts <30 min.

Insomnia

The Diagnostic and Statistical Manual of Mental Disorders 4th Edition text revision (DSM)-IV-TR defines primary insomnia (i.e., insomnia not caused by an underlying medical or psychiatric disorder) as “difficulty initiating or maintaining sleep, or non-restorative sleep, for at least one month, with the sleep disturbance (or associated daytime fatigue) causing clinically significant distress or impairment in social, occupational or other important areas of functioning” . Patients may use the word ‘insomnia’ to describe any sleep abnormality.

Restorative sleep (RS)

Restorative sleep describes the normal condition in which individuals feel refreshed and rested after sleeping.

Non-restorative sleep (NRS)

The DSM-IV defines NRS as “self-reported restless, light or poor quality sleep”. This is not always in agreement with the definition of NRS used in clinical FM studies, in which the sleep of participants may be considered NRS on the basis of the symptom of feeling unrefreshed after sleep of seemingly adequate latency, maintenance and duration .

Excessive sleepiness (ES)

Excessive sleepiness (ES) describes a tendency to fall asleep at inappropriate times while performing activities of normal daily living . It is worth noting that insomnia sufferers frequently find it difficult to sleep during daytime nap opportunities . The Epworth Sleepiness Scale (ESS) is an ES assessment instrument .

Fatigue and sleepiness

Exhaustion, a lack of energy and an overwhelming sense of tiredness characterise fatigue, which has to be strictly distinguished from ES. Among others, the Fatigue Severity Scale measures both mental and physical components.

As all of the above are prominent and overlapping symptoms in FM patients, it may be even more difficult to distinguish them .

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