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Definition

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Fibromyalgia (FM) is characterized by chronic widespread musculoskeletal pain and tenderness. Although it is defined primarily as a pain syndrome, FM patients also commonly complain of associated neuropsychological symptoms of fatigue, unrefreshing sleep, cognitive dysfunction, anxiety, and depression. Patients with FM have an increased prevalence of other syndromes associated with pain and fatigue, including chronic fatigue syndrome (Chap. 389), temporomandibular disorder, chronic headaches, irritable bowel syndrome, interstitial cystitis/painful bladder syndrome, and other pelvic pain syndromes. Available evidence implicates the central nervous system as key to maintaining pain and other core symptoms of FM and related conditions. The presence of FM is associated with substantial negative consequences for physical and social functioning.

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Epidemiology

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FM is far more common in women than in men, with a ratio of about 9:1. In population-based studies worldwide, there is general agreement that the prevalence rate is approximately 2–3%, with rates of closer to 5–10% in primary care practices. The prevalence data are similar across socioeconomic classes. Cultural factors may play a role in determining whether patients with FM symptoms seek medical attention; however, even in cultures in which secondary gain is not expected to play a significant role, the prevalence of FM remains in this range.

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Clinical Manifestations

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Pain and Tenderness

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The most common presenting complaint of a patient with FM is “pain all over.” Patients with FM have pain that is typically above and below the waist on both sides of the body and involves the axial skeleton (neck, back, or chest). The pain attributable to FM is poorly localized, difficult to ignore, severe in its intensity, and associated with a reduced functional capacity. Pain should have been present most of the day on most days for at least 3 months.

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The clinical pain of FM is associated with increased evoked pain sensitivity. In clinical practice, this is determined by a tender point examination in which the examiner uses the thumbnail to exert pressure of approximately 4 kg/m2, or the pressure leading to blanching of the tip of the thumbnail, on well-defined musculotendinous sites (Fig. 335-1). American College of Rheumatology classification criteria previously required that 11 of 18 sites be perceived as painful for a diagnosis of FM. In practice, tenderness is a continuous variable, and strict application of a categorical threshold for diagnosis specifics is no longer necessary. Increased pain sensitivity can be demonstrated not only for the mechanical pressure-induced pain used in the clinic but also for nonmuscular mechanical pressure, heat, cold, and other sensory stimuli; this reinforces the idea that the pathogenic mechanisms of FM are not related to specific musculoskeletal pathology but to altered pain processing. New criteria eliminate tender points and focus on clinical symptoms of widespread pain and neuropsychological symptoms.

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