Fibromyalgia: An Afferent Processing Disorder Leading to a Complex Pain Generalized Syndrome

Abstract

Fibromyalgia is a condition which appears to involve disordered central afferent processing. The major symptoms of fibromyalgia include multifocal pain, fatigue, sleep disturbances, and cognitive or memory problems. Other symptoms may include psychological distress, impaired functioning, and sexual dysfunction. The pathophysiology of fibromyalgia remains uncertain but is believed to be largely central in nature. In 1990 the American College of Rheumatology (ACR) published diagnostic research criteria for fibromyalgia. The criteria included a history of chronic and widespread pain and the presence of 11 or more out of 18 tender points. Pain was considered chronic widespread when all of the following are present: pain in the left side of the body; pain in the right side of the body; pain above the waist; pain below the waist. In addition, axial skeletal pain must be present and the duration of pain must be more than 3 months. A tender point is considered positive when pain can be elicited by pressures of 4 kg/ cm2 or less. For tender points to be considered positive, the patient must perceive the palpation as painful; tenderness to palpation is not sufficient. However, over the next 20 years it became increasingly appreciated that the focus on tender points was not justified. In 2010 a similar group of investigators performed a multicenter study of 829 previously diagnosed fibromyalgia patients and controls using physician physical and interview examinations, including a widespread pain index (WPI), a measure of the number of painful body regions. Random forest and recursive partitioning analyses were used to guide the development of a case definition of fibromyalgia, to develop new preliminary ACR diagnostic criteria, and to construct a symptom severity (SS) scale. The most important diagnostic variables were WPI and categorical scales for cognitive symptoms, un-refreshed sleep, fatigue, and number of somatic symptoms. The categorical scales were summed to create an SS scale. The investigators combined the SS scale and the WPI to recommend a new case definition of fibromyalgia: (WPI ≥ 7 AND SS ≥ 5). Although there is no known cure for fibromyalgia, multidisciplinary team efforts using combined treatment approaches, including patient education, aerobic exercise, cognitive behavioral therapy, and pharmacologic therapies (serotonin norepinephrine reuptake inhibitors [e.g., duloxetine, milnacipran] and alpha 2-delta receptor ligands [e.g., pregabalin]) might improve symptoms as well as function in patients with fibromyalgia. Key Words: Pain, fibromyalgia, fatigue, sleep, duloxetine, pregabalin, milnacipran