The Neural Plasticity Model of Fibromyalgia Theory, Assessment, and Treatment: Part 1
New developments in understanding chronic pain, suggest new methods for understanding fibromyalgia. Neural plasticity refers to the way the neurological systems (sensory, motor, and central) react and adapt to the repeated stimulation of chronic pain. Fibromyalgia and fibromyalgia syndrome are presented as an example of this phenomena. Part One of this series presents the basis for understanding fibromyalgia from the neural plasticity model, Part Two discusses assessment procedures, while Part Three develops a comprehensive treatment model.
The term “fibromyalgia” means pain of the muscle and surrounding fibrous tissues of the body. This term has now generally displaced the older term “fibrositis” which was suggestive of an inflammatory or degenerative musculoskeletal disorder. Although still medically classified as a soft tissue rheumatic disorder, as the older term “fibrositis” would imply, fibromyalgia (FM) is more correctly denotative of a generalized, persistent, idiopathic, musculoskeletal pain condition that is associated with the presence of numerous tender points that reliably discriminate this condition from other rheumatic conditions.1
The American College of Rheumatology (ACR) criteria for the diagnosis of FM for research purposes are widespread pain in all four quadrants of the body of at least three months duration and decreased pain threshold. Decreased pain threshold (allodynia) is operationalized by pressure dolorimetry at 18 designated tender point locations and the finding of a minimum 11 of these points as positive for pain at less than 4.0 kg/cm2 of applied pressure.1 FM tender points are displayed throughout the body including the neck, shoulders, chest, back, arms, hips and knees, but the 18 locations designated by the ACR are the most common locations across patients. The use of the ACR 1990 classification criteria for FM provides a sensitivity of 88 percent and a specificity of 81 percent in distinguishing FM from other musculoskeletal pain disorders.1 However, while tender point examination is a clinically reliable technique, 2,3 the presence of many tender points is also associated with depression, fatigue, anxiety, and other somatic symptoms as well as with pain.4,5 Moreover, pain sensitivity and tender point counts will vary as a function of menstrual cycle phase6 and the number of positive tender points less than the prerequisite 11 on early examination fails to predict the later development of fibromyalgia syndrome.7
Although not included as part of the ACR diagnostic criteria, the FM symptom complex also includes a number of other commonly associated symptoms, including sleep disturbances, morning stiffness, fatigue, poor immediate recall, poor concentration, and a decreased ability to multi-task.8,9 Added to the ACR 1990 diagnostic criteria for FM, these additional associated symptoms have come to be designated as “Fibromyalgia Syndrome” (FMS). (Except where otherwise specifically indicated, the term “fibromyalgia” (FM) will be used throughout this paper to designate both the more specific condition of fibromyalgia as well as the broader syndrome itself.)
The identification of FM is further complicated by the fact that it commonly coexists with other conditions and syndromes such as arthritis, chronic fatigue syndrome (CFS), depression and generalized anxiety, headache syndromes, irritable bowel syndrome (IBS), mitral valve prolapse (MVP), primary dysmenorrhea, restless leg syndrome (RLS), systemic lupus erythematous (SLE), temporomandibular joint dysfunction syndrome (TMJ), and myofascial pain syndromes (MPS). 10,11 In particular, FMS and CFS have a great many symptoms in common and a number of studies have shown that a majority of those diagnosed with CFS also meet the ACR 1990 criteria for a diagnosis of FM and, conversely, that more than 50 percent of persons diagnosed with FM also have a current or past diagnosis of CFS.12 Some researchers have pointed out that whether a person gets diagnosed with FMS or CFS is largely dependent on whether they complain more loudly of pain or of fatigue.
Regional soft tissue pain syndromes and FM also share many clinical and psychological features. However, several features, including poor sleep, persistent fatigue, irritable bowel symptoms, bloating, paresthesias, headaches, and number of trigger points are significantly less frequent or fewer in number among persons with regional soft tissue pain than those with fibromyalgia.13
Epidemiological studies have revealed fibromyalgia to be primarily a female disorder, with more than 80 percent of all cases being diagnosed in females14 and prevalent in approximately 2.015 to 3.3 percent16 of the North American population generally. There is also evidence that males with FM experience fewer symptoms and fewer tender points as compared to females with fibromyalgia.17 Although FM is seen in children, it is primarily prevalent between the ages of 40 and 64, with a mean age in the population of approximately 48 years.16 Wolfe15 suggests that many of the elderly population who are diagnosed with arthritis, may actually be suffering from FM, thus increasing the incidence rate for the 60 to 79 age range. Onset appears to be associated with a number of different factors including trauma to the neck,18 low back pain,19 viral infection,20 stress,21 and a combination of these factors. The development of FM has been noted to begin with localized pain in most cases, with a clearly increasing tendency for patients with regional and chronic multi-focal pain to develop chronic widespread pain and FMS.22 FM appears to be a chronic and relatively unchanging condition, with up to 85 percent of those diagnosed with the condition continuing to fulfill the diagnostic criteria after four years23 and an average length of time in pain reported as 78.7 months.20
With the passing of a full decade of extensive research and investigation since the development of the ACR classification criteria, the etiology and consequently the treatment of FM continue to be poorly understood. Moreover, although a very small minority, there are still some “doubting Thomases” that insist that FM is not a real medical condition.24