Primary care physicians are often faced with the challenge of caring for patients with fibromyalgia syndrome (FMS). FMS is a complex condition characterized by pain amplification, musculoskeletal discomfort, and systemic symptoms. In the United States, it is the third or fourth most common reason for a rheumatology referral.
Definition
Approximately 10% to 12% of the general population has widespread chronic pain. FMS is a concept designed to account for such generalized chronic and idiopathic pain. The 1990 classification criteria of the American College of Rheumatology (ACR) is based on the analysis of more than 300 variables such as symptoms, physical findings, and laboratory and radiologic studies by a study committee.1 The mandatory defining symptom is widespread pain not explained by an inflammatory or degenerative musculoskeletal disorder.
The ACR criteria for diagnosis of FMS have two components. The first is widespread pain for at least 3 months (pain in the left side of the body, plus right side of the body, plus pain above the waist, plus pain below the waist, plus axial pain; axial pain includes pain in the cervical spine, or thoracic pain, or pain in the low back or anterior chest wall). The second is the presence of 11 tender points among 18 specified sites as shown in Figure 1. Pressure of 4 kg/cm (enough to whiten the examiner’s fingernail) should be applied to each point for a few seconds.2
It is important to remember that there are more than 600 muscles in the human body, each of which might theoretically contain a tender point. The 18 tender points recommended by the ACR represent only a sample of widespread pain in any given patient. If a patient has widespread pain in many other areas, it is entirely possible that he or she has fibromyalgia.3
The presence of many tender points on digital palpation validates the diagnosis. According to the ACR criteria, the finding of 11 of 18 specified tender points provided a sensitivity of 88% and a specificity of 81% in distinguishing fibromyalgia from other chronic causes of musculoskeletal pain. 1 In addition, the criteria committee found that several other disorders are often associated with FMS, including sleep disturbance, fatigue, paresthesias, anxiety, and headache or irritable bowel syndrome. Frederick Wolfe, the chairman of the criteria committee, later wrote that the presence of seven (40%) of the tender points and at least three of the six features mentioned earlier are highly suggestive of FMS.
It is now widely accepted that numerous other conditions can overlap with FMS (Box 1). These include irritable bowel syndrome, tension-type headaches, migraine, temporomandibular dysfunction, myofascial pain syndrome, chronic fatigue syndrome, restless legs syndrome, and multiple chemical sensitivities, to name just a few.
Box 1: Conditions Commonly Associated with Fibromyalgia
Cognitive dysfunction
Cold intolerance
Dizziness
Dysautonomia
Endocrine dysfunction
Interstitial cystitis
Irritable bladder syndrome
Irritable bowel syndrome
Migraine headaches
Multiple chemical sensitivities
Myofascial pain syndrome
Sicca symptoms
Temporomandibular joint dysfunction
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Prevalence
Pain on digital palpation test
Figure 1: Click to Enlarge
The prevalence of FMS in the general community is 2% for both genders. Women are affected more than men; the prevalence is 3.4% for women and 0.5 % for men. The prevalence increases with age, reaching 7% in women ages 60 to 79 years.4
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Pathophysiology
A heightened pain response is present in patients with FMS. This is now known to be caused by altered processing of nociceptive stimuli by the central nervous system.5,6 Levels of substance P and abnormal antinociceptive peptides are elevated in the cerebrospinal fluid of patients with FMS.7 FMS might be best understood as a heightened response of the entire nervous system, as if the volume has been turned up.8,9 Inheritance of a short allele of the serotonin transporter promoter gene has taken serotonin metabolism to center stage and suggests a possible heritable mechanism in the pathogenesis of FMS.10 Other studies have postulated serotonin deficiency as a pathophysiologic mechanism in FMS.11 A group of excitatory amino acids—l-tryptophan, alanine, histidine, lysine, proline and serine, to name a few—are also decreased in the spinal fluid in patients with FMS.12
Although some reports have suggested that muscle tissue is normal in FMS, others have found increased moth-eaten and ragged red type I and type II fiber atrophy on light microscopy.13,14 Other clinicians have found myofibril lysis or swollen abnormal mitochondria on electron microscopy.13,14 However, it is unclear whether these changes are due to deconditioning or to FMS itself.2
Slow-wave sleep abnormalities are also present, and a significantly increased amount of alpha-wave intrusion into delta-wave sleep during non–rapid eye movement (non-REM) sleep is responsible for more awakenings and other symptoms of nonrestorative sleep. Sleep apnea and restless legs syndrome, nocturnal myoclonus, and bruxism have been reported in some studies. 2 Severe dysautonomia, or reflex sympathetic dystrophy, coexists with FMS and is believed by some clinicians to be a subtype of FMS. 2
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Predisposing Factors
One half of all FMS cases have no apparent cause. The most common cause of secondary FMS is trauma. Even trivial trauma can act as the inciting agent and lead to the development of widespread pain within 3 months. Numerous infectious agents such as herpes viruses, parvovirus, Borrelia burgdorferi, human immunodeficiency virus, and Brucella species have been implicated as the causes of a postinfectious fatigue–like syndrome. 2 To date, however, no clinical or serologic studies have proved an etiologic role for Epstein-Barr virus, parvovirus or, indeed, any virus. Heavy lifting and bending, or prolonged sitting at word processing stations, might induce secondary FMS. Heroin, cocaine, and alcohol withdrawal can also induce a FM-like syndrome, as can administration of interferon alfa or interleukin-2. Life-altering events such as death of a loved one, loss of a job, or divorce in the presence of poor coping mechanisms can bring out FMS. 2 Emotional trauma such as physical or sexual abuse or posttraumatic stress disorder can act as triggers.