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Fibromyalgia, Chronic Fatigue, and Chronic Fatigue Syndrome

Clinicians can benefit from a clearer distinction between 3 overlapping syndromes that are each impacted by sleep and symptoms of depression.
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Editor’s Note: This article is excerpted from Dr. Goldenberg’s new book, Chronic Widespread Pain: Lessons Learned from Fibromyalgia and Related Disorders. To purchase the entire e-book, go to and use the promo code READPPM for a 15% discount.

Persistent exhaustion is almost always present in patients with fibromyalgia (FM) and is prominent in each of the overlapping chronic functional illnesses, including irritable bowel syndrome (IBS), chronic migraine, and chronic bladder and pelvic pain. Unfortunately, there is no universal definition of what constitutes pathologic fatigue. The most common description of excess fatigue suggests that it is an extreme and persistent form of mental and/or physical tiredness, weakness, or exhaustion.

Chronic fatigue, like chronic pain, is a common symptom in the general population, with prevalence estimates between 10% and 40%.

Unexplained chronic fatigue, like FM, was described in the 1800s. In 1869, Dr. George Beard reported severe exhaustion accompanied by a constellation of symptoms, including “headaches, dyspepsia, insomnia, anesthesia, neuralgia, and rheumatic gout,” the term used at that time for joint and muscle pain.1 Beard termed this neurasthenia (chronic exhaustion) and suggested it resulted from changes in the central nervous system: “My own view is that the central nervous system . . . probably undergoes slight, undetectable, morbid changes in its chemical structure and as a consequence becomes more or less impoverished in the quantity and quality of its nervous force.”1

Chronic fatigue, like chronic pain, is a common symptom in the general population, with prevalence estimates between 10% and 40%. In 1 study, nearly 20% of 31,000 men and women (age 18 to 45) in a general practice reported substantial fatigue lasting 6 months or longer.2 During the past decade, most studies have defined chronic fatigue as fatigue lasting 6 months or longer with fatigue scores of 8 or greater on the Fatigue Scale.3 Women are more likely to report fatigue and more often report severe fatigue.2-4 The prevalence of fatigue was 30% in older women compared with 15% in older men.5

Chronic pain and chronic fatigue are strongly associated. In a general population-based survey, chronic fatigue (occurring in 5% to 12%) overlapped with chronic widespread pain, chronic orofacial pain, and IBS.6 The occurrence of multiple syndromes was greater than would be expected by chance. Factors that were common across syndromes included female gender and high levels of anxiety related to health, such as medical worry preoccupation.

In a second study, the authors reported persistent fatigue in 60% of the 451 subjects with chronic widespread pain, and chronic widespread pain was reported in 33% of 809 responders who had persistent fatigue.7 In addition, anxiety and depression were more common in subjects who reported both symptoms than in those who reported either 1 or neither. “Participants who had chronic disease, high body mass index, low activity levels, or did not perceive ability to influence health, had higher adjusted odds of reporting both symptoms [but not 1 alone] than subjects not having these characteristics,” noted the authors.7

What Causes Chronic Fatigue?

The most common causes of fatigue are chronic medical or psychiatric illnesses, accounting for 70% of chronic fatigue in the general population. However, at least 30% of the time no specific cause is found for chronic fatigue.8

In population-based studies, it has been very difficult to separate idiopathic chronic fatigue that has been associated with chronic depression and other chronic mood disturbances. Depression-associated fatigue versus “pure” fatigue was evaluated in a report that prospectively followed 1,177 primary care patients, with 3 separate measurements of fatigue and psychiatric symptoms.9 The depression and fatigue scores correlated closely over time. They replicated previous findings of a strong correlation between fatigue and psychiatric morbidity, but also identified a group of patients with persistent, independent fatigue, which was not associated with any increase in psychological morbidity. This persistent, independent fatigue state (lasting for 6 months) was uncommon and found in only 2.5% of the population.

In data from the second British National Survey of Psychiatric Morbidity, “the prevalence of chronic fatigue was 15% and this was significantly associated with the number of reported physical illnesses. Chronic fatigue was strongly associated with the presence of depressive symptoms [OR 5.37], anxiety-related symptoms [OR 4.66], and sleep complaints [OR 4.41]. After adjustment for all sociodemographic and psychiatric factors, the number of reported physical illnesses was less strong but still significantly associated with chronic fatigue.”10

In a population survey of more than 10,000 adolescents, 13 to 18 years old, chronic fatigue was found in 3%, of which one-half had associated depression or anxiety.11 Although the prevalence is lower than in adults, more than half the adolescents with chronic fatigue had severe or very severe disability. Comorbid mood correlated with greater disability and health service utilization.

In a study of adults over 60, the overall prevalence of fatigue was 27%, much higher than that seen in adolescents.12 As with younger adults, most cases were associated with a psychological disorder, and psychological disorders were more predictive of chronic fatigue than physical illness. However, distinct forms of physical and psychological fatigue could be identified.

Assessment of Chronic Fatigue

In an observational cohort study involving 147 primary care practices, the authors described 4 distinct patterns of chronic fatigue: “26% of patients had continuously high scores for fatigue, 17% had a fast recovery, 25% had a slow recovery, and 32% initially improved but then had a recurrence of fatigue.”13 The authors also found a longitudinal relationship with fatigue severity and impaired functioning, psychological symptoms, and poor sleep. These same investigators reported that changes in pain and fatigue were directly related in time.14

There are 3 different instruments commonly used to measure fatigue: the Patient-Reported Outcome Measurement Information System (PROMIS) instrument, the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F), and the SF-36v2 Vitality subscale.15 Fatigue was associated with gender, being significantly more common in younger females. Greater education and being married correlated with less fatigue.

In order to better characterize fatigue states in various subspecialties, a cross-sectional sample of women with chronic fatigue syndrome (CFS), post-cancer fatigue, or fatigue associated with depression were evaluated with a specific instrument.16 The instrument was able to differentiate CFS from major depression.

Last updated on: December 13, 2016
First published on: December 1, 2016
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