Diagnostic and Clinical features of Myofascial Trigger Points
Diagnostic Criteria
The diagnosis of myofascial TrPs depends on the history and on its confirmation by physical examination. There is poor agreement among authors as to the most appropriate diagnostic criteria. Numerous clinical features have been associated with myofascial TrPs, but only recently have interrater reliability studies been reported that give some guidelines. No satisfactory laboratory or imaging test is currently available for making the diagnosis of myofascial TrPs.
Clinical Features
Several clinical features are commonly associated with the diagnosis of myofascial TrPs (31); these include a confusing mixture of sensory and motor phenomena: History of spontaneous localized pain associated with acute overload or chronic overuse the muscle. The mildest symptoms are caused by latent TrPs that cause no pain but cause some degree of functional disability. More severe involvement results in pain related to the position of the muscle or muscular activity. The most severe level involves intermittent or continuous pain at rest (32).
The precise pattern of pain described by the patient is THE most valuable clue for finding where the TrP is located. Recognizing the pattern of pain as characteristic of a particular muscle tells the clinician where to look for the TrP or TrPs that are responsible for at least part of the patient's pain.
Palpable Band
A cord-like band of fibers is palpable in the involved muscle. This band helps to locate spot tenderness, but it may be inaccessible because of overlying muscles or thick [or tense] subcutaneous tissue. Its tendon attachment may evidence the spot tenderness of enthesopathy (23).
Spot Tenderness
This involves a VERY tender and VERY small spot which is foundin a palpable band when the band is accessible to palpation. The sensitivity of this spot [the TrP] is increased by increasing the tension on the muscle fibers of the taut band.
Jump Sign
Pressure on the spot of tenderness causes the patient to physically react to the pain with a spontaneous exclamation or movement. This finding gives an indication of the degree of spot tenderness, but the results are strongly dependent on the amount of pressure exerted by the examiner (33).
Pain recognition
Digital pressure on a tender spot [the TrP] or needle injection of an active locus active locus induces at least some of the pain of which the patient complains, and the patient recognizes it as his or her pain. This finding by definition identifies an active TrP.
Twitch Response
The local twitch response is a transient contraction of the fibers of the taut band associated with a TrP; it can be elicited by vigorous snapping palpation of the taut band [when accessible] at the TrP or by needle penetration of an active locus in the TrP. The latter is an important phenomenon for assuring effective injection of a TrP. Snapping palpation is effective only in a taut band that is in a sufficiently superficial and accessible muscle; it also requires much skill.
Elicited Referred Pain and Tenderness
An active: TrP refers pain in a pattern characteristic of that muscle (31,34). The pain is often not located in the immediate vicinity of the TrP, but is referred to a distance. On initial examination, the patient is often surprised at the location and tenderness of the TrP. Eighty-five percent of the reported pain patterns (31,34) project distally (35). The deep tissue nature of the referred pain that is described by patients is substantiated by Vecchiet, et al. (36), whose study demonstrated the persistence of deep tenderness in the reference zone for a day or more after injection of hypertonic saline into a proximal limb muscle. Subcutaneous tissue was found to be more tender than the skin over both TrPs and FM tender Points (37).
Unfortunately, when the referred pain is elicited by the application of pressure to a tender location it is a non-specific finding (38). Whether one elicits only local pain, referred pain, or reaches pain tolerance depends upon the amount of pressure applied (33).
Elicited referred pain does not clearly distinguish latent TrPs from active TrPs; latent TrPs simply require more pressure (33).
Restricted Range of Motion. Full stretch range of motion of the affected muscle is restricted by pain. This restriction is relieved by the release of the palpable taut bands through inactivation of associated TrPs. The importance of this finding is relatively muscle-specific because it varies considerably from muscle to muscle; therefore, it is more useful as a diagnostic criterion in some muscles than in others. When movement is markedly restricted, measurement of increase in range of motion becomes a useful objective measure of progress. Relatively inexpensive, accurate, and convenient electronic inclinometers are now available for measuring range of motion. The restricted range of motion of patients with active TrPs provides an objective diagnostic distinction from patients with FM who characteristically show joint hypermobility (39).
Muscle weakness
Clinically, the patient is unable to develop normal strength on static testing, as compared to testing of a contralateral uninvolved muscle. Static strength is measurable using a force meter. Dynamic testing of muscles with active TrPs is just beginning to be explored using surface electromyographic [EMG] techniques. The involved muscle may initially evidence fatigue, which is indicated by increased average amplitude of integrated EMG (40). Reduced mean spectral frequency and reduced forcefulness of movement look promising as additional measures of "initial fatigue" in pilot studies.
Interrater Reliability
Many of the features described above have not been tested for interrater reliability, but some have been. Four studies evaluated the reliability of myofascial TrP examinations. Results are summarized in Table 3. In 1992 Wolfe, et al. (12) reported a study, part of which involved the evaluation of 8 muscles in 8 patients by 4 physicians experienced in examining patients for TrPs. The muscles examined included the levator scapulae, supraspinatus, anterior scalene, upper trapezius, infraspinatus, pectoralis major, sternocleidomastoid, and the iliocostalis/longissimus muscles in the TlO-L1 region. The four examiners had no chance to agree on a technique for examining the upper body TrPs prior to this study. The physicians examined each muscle for 5 findings characteristic of TrPs [Table 3]. Since recent studies report interrater reliability results in terms of the kappa statistics, two co-authors of this study [Simons and Skootskyl analyzed the original data for the kappa statistic, which also corrects for chance agreement [Table 3]. In 1992 Nice, et al. (41) reported on the examination of three sites in the thoracolumbar paraspinal muscles of 50 patients with low back pain by 12 experienced full-time physical therapists who routinely treated patients with low back pain. "A practice session was held to allow the therapists to practice this method on each other until all physical therapists reported that they felt capable of using the method on patients" (41). In 1994, Nice et al. (42) reported on the examination of 2 muscles [quadratus lumborum and gluteus medius] in 6l patients with low back pain by 2 examiners picked from a pool of 1 physician in general practice and 4 medical students trained over a 3 month period by the physician. The average kappa values for the 6 examinations were essentially equal for the quadratus lumborum and gluteus medius muscles, indicating that those muscles were about equally difficult to examine. Currently, Gerwin, et al. (43) have reported a study in which 4 physicians examined 5 muscles in each of 10 subjects with myofascial TrPs. Following a three-hour training session,agreement among doctors was assessed statistically before proceeding with the study. Examination of the extensor digitorum communis and latissimus dorsi muscles was most reliable. Examination of the sternocleidomastoid and upper trapezius muscles was less reliable, and examination of the infraspinatus muscle was least reliable. Presumably it was the most difficult to examine. A number of inferences can be drawn from Table 3. The poor reliability in the first two studies (12,41) can be attributed to inadequate training of experienced examiners. The improved performance in the third study (42) reflects considerable training of inexperienced examiners. The more extensive training of experienced examiners in the fourth study (43) corresponds to a marked improvement in kappa values. Fricton (7), in a diagnostic study of masticatory myofascial pain, found that experienced raters were more reliable than inexperienced raters and concluded that findings by palpation are technique sensitive. Table 4 shows a comparison of the examinations summarized in Table 3. It can be seen in Table 4 that spot tenderness, jump sign, and pain recognition were the examinations most reliably performed. The examinations for a palpable band and for referred pain appear highly sensitive to the amount of training; the twitch-response appeared to be the most demanding off training and skill.
Value of Clinical Features as Diagnostic Criteria
An early attempt to identify the most appropriate diagnostic criteria under different circumstances (44) suffered from the absence of interrater reliability studies. Since no studies have been reported that evaluate the discriminating power of the clinical characteristics of TrPs, including the history, one can only estimate their likely diagnostic value [Table 4] based <,n information now available.
The finding of a palpable taut band alone is ambiguous because it is often seen in normal subjects (12,42).
The value of spot tenderness alone is limited because of ambiguity with regard to tender points of FM and other focal painful conditions. However, the presence of spot tenderness in a palpable band would likely provide good discrimination if the examiners were skillful at detecting the taut band. If quantification of spot tenderness is desired, properly administered algometry should be superior to manual testing for the jump sign.
Pain recognition is a reasonably reliable test in trained hands and has much clinical significance.
Referred pain, per se, is likely to have little discriminating power. Although the manually elicited twitch response is the most demanding of operator skill, it has the potential of providing the best discrimination of any single measure when the taut band and TrP are in an accessible location.
