Monopolar needle electromyogram (EMG) was recorded simultaneously from trapezius myofascial trigger points (TrPs) and adjacent nontender fibers (non-TrPs) of the same muscle in normal subjects and in two patient groups, tension headache and fibromyalgia. Sustained spontaneous EMG activity was found in the 1-2 mm nidus of all TrPs, and was absent in non-TrPs. Mean EMG amplitude in the patient groups was significantly greater than in normals. The authors hypothesize that TrPs are caused by sympathetically activated intrafusal contractions.
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"In 1959, Travell reported that TrPs may have a unique electromyographic signature (Travell, 1959) and in 1966, Arroyo found continuous motor activity only in the region of TrPs (Arroyo, 1966). It is was not until 1993, however, that Hubbard and coworkers confirmed spontaneous electrical activity at TrPs (Hubbard and Berkoff, 1993). Previous efforts to identify such activity had failed mostly because of methodological issues or poor definitions of myofascial pain. "
"Gerwin (2014) provided a comprehensive review of the definition, identification, causative factors, and differential diagnosis of myofascial pain syndrome and the TrP as its central feature. Although objective diagnostic identification is becoming possible using vibration sonoelastography with ultrasound (Sikdar et al., 2009), magnetic resonance elastography (Chen et al., 2008), and electromyography (Hubbard and Berkoff, 1993), clinically the diagnosis of TrPs is made through a thorough history, accurate palpation, presence of referred pain, diminished range of motion, muscle inhibition, and autonomic changes. Additionally, the author provided clinical insights to palpation including manual compression of a TrP for a minimum of 5e10 s to induce referred pain to allow activation of interneurons for central sensitization. "
"This agrees with a previous report which found that lidocaine produces better results in patients with mechanical allodynia at baseline than in those who did not have this symptom. Several reports show substantial evidence of the presence of spontaneous electrical activity in the TrPs[17,18,262728. The reduction of trapezius EMG activity at rest and during swallowing of saliva in the lidocaine group is in agreement with the findings of Bahadir et al., who found that ultrasound or local injection of lidocaine were equally effective in lowering the spontaneous electrical activity. "
[Show abstract][Hide abstract] ABSTRACT: Objective:
To compare the effects of 5% lidocaine patches and placebo patches on pain intensity and electromyographic (EMG) activity of an active myofascial trigger point (MTrP) of the upper trapezius muscle.
Materials and methods:
Thirty-six patients with a MTrP in the upper trapezius muscle were randomly divided into two groups: 20 patients received lidocaine patches (lidocaine group) and 16 patients received placebo patches (placebo group). They used the patches for 12 h each day, for 2 weeks. The patch was applied to the skin over the upper trapezius MTrP. Spontaneous pain, pressure pain thresholds, pain provoked by a 4-kg pressure applied to the MTrP and trapezius EMG activity were measured before and after treatment.
Baseline spontaneous pain values were similar in both groups and significantly lower in the lidocaine group than the placebo group after treatment. The baseline pressure pain threshold was significantly lower in the lidocaine group, but after treatment it was significantly higher in this group. Baseline and final values of the pain provoked by a 4-kg pressure showed no significant difference between the groups. Baseline EMG activity at rest and during swallowing of saliva was significantly higher in the lidocaine group, but no significant difference was observed after treatment. Baseline EMG activity during maximum voluntary clenching was similar in both groups, but significantly higher in the lidocaine group after treatment.
These clinical and EMG results support the use of 5% lidocaine patches for treating patients with MTrP of the upper trapezius muscle.
Full-text · Article · Nov 2014 · Acta Odontologica Scandinavica