Recent findings suggest an association between sleep disturbances and pain the following day in fibromyalgia patients.
Fibromyalgia is currently viewed as a central nervous system disorder of unknown etiology characterized by chronic widespread musculoskeletal pain and tenderness at specific anatomical sites (tender points). In 1990, the American College of Rheumatology established reliable diagnostic criteria for fibromyalgia, which includes painful response to pressure in at least 11 of 18 specific tender points. These diagnostic criteria are commonly used in research protocols. Diagnosis of fibromyalgia in the community is often made even when fewer than 11 tender points are present and is based on other clinical symptoms. Fibromyalgia is frequently associated with symptoms that are not musculoskeletal including, but not limited to, fatigue, dyssomnia, depression, anxiety, headaches, and irritable bowel syndrome. Yunus1 has suggested a biopsychosocial model of fibromyalgia syndrome (FMS) involving a complex interaction between genetic, neuroendocine, psychological, poor sleep, and environmental factors. The present study focuses on sleep disturbance and psychological factors in relation to reported pain and fatigue in a community-based sample of fibromyalgia patients.
The most common non-musculoskeletal symptoms associated with fibromyalgia are fatigue and sleep disturbances. The major sleep symptoms observed in fibromyalgia patients are perception of unrefreshing sleep and the presence of intrusion of fast EEG during the deepest stages of sleep (referred to as alpha-delta sleep). Whereas alpha-delta sleep, the objective sleep finding in fibromyalgia, is present in less than half of fibromyalgia patients, the subjective perception of unrefreshing sleep and fatigue is reported by the majority of fibromyalgia patients.2 It has been suggested that sleep disturbance may affect both pain levels and emotional distress among patients with fibromyalgia. The relationship between subjective measures of sleep and pain has been recently studied by Affleck and colleagues3 who found that individuals who reported poorer sleep tended to also report more pain. Moreover, within subjects, a night of poorer sleep was associated with greater pain and with greater attention to pain on the following day. Similarly, a day with more pain (and greater attention to pain) was followed by a night of poorer sleep. Thus, the relationship between sleep and pain (and with its correlate—attention to pain) appears to be bidirectional. It is not clear what factors influence attention to pain and reported pain. Perception of stress, depression, alexithymia, and somatization have been reported as correlates of pain and the first of these four has also been linked with disturbed sleep.
We have recently examined the relationship between subjective measures of sleep and the severity of reported pain and fatigue in a sample of 22 clinic-based female fibromyalgia patients. Ages ranged from 39 to 79 with an average age of 54 years, and the number of years since the initial diagnosis of fibromyalgia ranged between 1 and 7 years with an average of 3.9 years. Upon consenting to participate in the study, the patients had a physical examination during which a clinician assessed the number of tender points and the severity of pain in each point on the basis of the patient’s behavioral response to manual pressure. The average number of tender points was 11.6 and the average total severity score was 18.8.
Participants also completed a battery of questionnaires and were given a daily sleep-pain diary, which was kept during the following week. Questionnaires included the following five instruments: the Beck Depression Inventory (BDI), which is a widely used 21-item depression inventory; the Modified Somatic Perception Questionnaire (MSPQ), which measures somatization as reflected by the level of 13 diffused physical complaints; the Perceived Stress Scale; the Fatigue Severity Scale; and the Toronto Alexithymia Scale, which measures awareness of emotional experiences.
Diaries were completed twice each day, at bedtime and on awakening. Sleep parameters were recorded every morning on awakening. Two sleep variables were derived from the diary entries, sleep efficiency and lingering in bed. Sleep efficiency provides a good overall index of disturbed sleep. Insomnia patients typically have sleep efficiencies below 0.85. Sleep efficiency was computed as the percent of total sleep time relative to total time in bed, whereas total sleep time was defined as the difference between time spent in bed and time spent awake while in bed (including time to sleep onset and time awake in the middle of the night). Lingering in bed was computed as the difference between the time out of bed and the time of waking up. Though lingering in bed is not a standard sleep measure, it could provide a link between sleep behavior and pain behavior. Morning diary entries included pain and fatigue visual analog severity scales with 0 indicating no pain (or no fatigue) and 10 indicating worst pain (or continuous fatigue). Participants also recorded the number of daily naps, and the total time they napped during the day. Participants also rated their “level of activity” and “how much energy was needed to invest in accomplishing tasks today.” Each diary-based variable was averaged over the 7-day recording period.
The data indicate that for fibromyalgia patients, both the severity of the disease and the self-ratings of pain were significantly correlated with subjective sleep measures. In particular, greater sleep disturbance and greater morning difficulties were associated with more tender points, greater pain at tender points during a physical examination, and greater average daily pain ratings. Smaller sleep efficiencies were associated with reports of more diffused pain (greater MSPQ scores), which in turn were significantly correlated with greater difficulty getting out of bed in the morning and with greater average daily fatigue. Smaller sleep efficiencies were also associated with larger depression scores (BDI), which were significantly correlated with average daily pain. It is important to keep in mind that elevated depression scores are not synonymous with being depressed. Greater alexithymia scores were significantly correlated with reports of poorer sleep quality as rated each morning by the patient.
This study does not report causality, but rather an association between variables measuring sleep pain, fatigue, and five psychological constructs. Pain disturbs sleep and insufficient sleep in turn increases pain and suffering. Sleep disturbances are common in depression and at the same night poor sleep is commonly associated with mood alteration. Experiencing more fibromyalgia-related pain increases suffering and decreases tolerance to other types of physical discomfort, thus leading to elevated MSPQ scores. There is a complex relationship between all these variables with no basis for causal inference. One intriguing finding is the unexpected association between poor sleep and lower perceived stress. Although insomnia tends to increase during periods of increased stress, poorer sleep in this sample was associated with lower levels of perceived stress. The fact that poorer sleep was associated here with greater alexithymia and greater somatization, two intercorrelated measures, suggests that lower perceived stress among FMS patients might be related to lower awareness of emotional processes. Alternatively, it is possible that with increased disease activity, FMS patients cope with pain by avoiding stressful situations and consequently experience less stress.
Rachel Manber, PhD, is director of the insomnia program at Stanford Sleep Disorders Center and an associate professor in the Department of Psychiatry and Behavioral Sciences at Stanford University, Palo Alto California. Les Castro, PhD, is research instructor at the Arthritis Center at the University of Arizona, Tucson.
References
1. Yunus M. Psychological aspects of fibromyalgia syndrome: a component of the dysfunctional spectrum syndrome. Baillieres Clin Rheumatol. 1994;8:811-837.
2. Carette S, Oakson G, Guimont C, Steriade M. Sleep electroencephalography and the clinical response to amitriptyline in patients with fibromyalgia. Arthritis Rheum. 1995;38:1211-1217.
3. Affleck G, Urrows S, Tennen H, Higgins P, Abeles M. Sequential daily relationship of sleep, pain intensity, and attention to pain among women with fibromyalgia. Pain. 1996;68:363-368.
