Natural Course of Myofascial Trigger Points

Only one longitudinal study is known that examined the muscles for taut bands and for evidence of TrP tenderness in a normal population to learn the incidence of TrPs. Fricton,et a1.(45) examined 269 female nursing students initially, again at 18 months and at 36 months for evidence of masticatory myofascial pain attributable to TrPs. They found an annual incidence of 8% with 5% developing masticatory myofascial pain only, and with 3% developing mixed myofascial pain and disk displacement in the temporomandibular joint. Additional studies will give us a more complete picture of what the natural course of myofascial TrPs may be. Figure 1 outlines a proposed natural course of myofascial pain caused by TrPs, based on information now available. The common presence of taut bands in pain-free individuals (12,42) suggests that taut bands are a necessary precursor to the development of TrPs. Some individuals appear to be genetically more vulnerable to the development of taut bands than others. Apparently, because of stressful life events and abnormal muscle stress (46) combined with genetic predisposition, a latent TrP develops in a taut band. This TrP, with further mechanical stress or other aggravating [perpetuating factors, can develop into an active TrP. The active TrP may recover spontaneously, may persist without progression, or, in the presence of perpetuating factors, the individual may develop additional TrPs and a chronic myofascial pain syndrome. Although in the past it had been assumed that TrPs caused a taut band (31,35), it now appears more likely that a taut band is a necessary precursor to the development of a TrP. In one study (12) taut bands were found to occur with nearly equal frequency in control subjects, myofascial pain patients, and FM patients. This indicates that neither myofascial pain nor FM significantly influences the number of taut bands present. A more recent study (42) reported that both examiners [100% agreement] found taut bands present in 6 of 63 [nearly 10%] of normal control subjects. These bands were the only suggestion of TrPs found in these normal subjects, who were free of spot tenderness. In 1989, Pellegrino, et a1.(47) reported clinical signs and symptoms that they identified as primary FM, but the description fit a diagnosis of myofascial TrPs much better than it fit FM (48). They described "abnormal, palpable muscle consistency years before acquiring clinical symptoms in teenage twins" (47). There are no studies which indicate that palpable bands are a diagnostic criterion for tender points of FM, but there is much clinical experience (31) and experimental evidence (49,50) that taut bands are an integral part of the TrP phenomenon. This study of 17 families (47) suggests that a proclivity to develop taut bands is an inherited characteristic and that those who are more prone to develop taut bands are also more likely to develop TrPs. In addition to general agreement among clinicians (2,4,7,8), the only documented evidence that muscle overload can initiate TrPs or convert a latent TrP into an active one is the study by Fricton, et a1.(46). Specifically, the course of an untreated latent TrP has not been studied. An incidence study of masticatory myofascial pain suggests that a latent TrP probably persists, with occasional increase in activity sufficient to cause symptoms become an active TrP]. An active TrP sometimes regresses without treatment to a latent TrP (45). Latent TrPs have been known to persist for many years, painlessly restricting range of motion, and then respond immediately to spray-and-stretch therapy. After an individual develops an active TrP, especially in the absence of any perpetuating factor, continuing normal gentle daily activity and avoiding muscle overload often permit spontaneous regression from an active TrP to a latent one in a few days to a few weeks. The presence of perpetuating factors assures persistence of an active TrP and sets the stage for the development of secondary TrPs, additional symptoms, and chronicity with progressive functional disability and psychological distress (31,34). The presence of perpetuating factors is one of the most common, and often one of the most important, factors in the management of patients with chronic myofascial TrPs (6,8,34). Recently, Gerwin demonstrated that iron insufficiency is a risk factor for myofascial pain caused by TrPs (51).

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