J Headache Pain. 2011 Feb;12(1):35-43. Epub 2011 Feb 27.
Referred pain from myofascial trigger points in head and neck-shoulder muscles reproduces head pain features in children with chronic tension type headache.
Fernández-de-Las-Peñas C, Fernández-Mayoralas DM, Ortega-Santiago R, Ambite-Quesada S, Palacios-Ceña D, Pareja JA.

Department of Physical Therapy, Occupational Therapy, Rehabilitation and Physical Medicine, Facultad de Ciencias de la Salud, Universidad Rey Juan Carlos, Avenida de Atenas s/n, 28922, Alcorcón, Madrid, Spain,

Abstract
Our aim was to describe the referred pain pattern and areas from trigger points (TrPs) in head, neck, and shoulder muscles in children with chronic tension type headache (CTTH). Fifty children (14 boys, 36 girls, mean age: 8 ± 2) with CTTH and 50 age- and sex- matched children participated. Bilateral temporalis, masseter, superior oblique, upper trapezius, sternocleidomastoid, suboccipital, and levator scapula muscles were examined for TrPs by an assessor blinded to the children’s condition. TrPs were identified with palpation and considered active when local and referred pains reproduce headache pain attacks. The referred pain areas were drawn on anatomical maps, digitalized, and also measured. The total number of TrPs was significantly greater in children with CTTH as compared to healthy children (P < 0.001). Active TrPs were only present in children with CTTH (P < 0.001). Within children with CTTH, a significant positive association between the number of active TrPs and headache duration (r (s) = 0.315; P = 0.026) was observed: the greater the number of active TrPs, the longer the duration of headache attack. Significant differences in referred pain areas between groups (P < 0.001) and muscles (P < 0.001) were found: the referred pain areas were larger in CTTH children (P < 0.001), and the referred pain area elicited by suboccipital TrPs was larger than the referred pain from the remaining TrPs (P < 0.001). Significant positive correlations between some headache clinical parameters and the size of the referred pain area were found. Our results showed that the local and referred pains elicited from active TrPs in head, neck and shoulder shared similar pain pattern as spontaneous CTTH in children, supporting a relevant role of active TrPs in CTTH in children.

Capsaicin-Induced Central Sensitization Evokes Segmental Increases in Trigger Point Sensitivity in Humans
Srbely, J.Z., Dickey, J.P., Bent, L.R., Lee, D., Lowerison, M. 2010 Journal of Pain 11 (7), pp. 636-643 0

This study investigated whether inducing central sensitization evokes segmental increases in trigger point pressure sensitivity. We evoked central sensitization at the C5 segment and validated its presence via mechanical cutaneous sensitivity (brush allodynia) testing. Trigger point pressure sensitivity was quantified using the pain pressure threshold (PPT) value.

A 50 cm2 area of the C5 dermatome at the right lateral elbow was pretreated with 45° heat for 10 minutes. Test subjects (n = 20) then received topical capsaicin cream (0.075%; Medicis, Toronto, Canada) to the C5 dermatome, whereas control subjects (n = 20) received a topical placebo cream (Biotherm Massage, Montreal, Canada). PPT readings were recorded from the infraspinatus (C5,6) and gluteus medius (L4,5S1) trigger points at zero (pre-intervention), 10, 20, and 30 minutes after intervention; all PPT readings were normalized to pre-intervention (baseline) values. T

he difference between the PPT readings at the 2 trigger point sites represents the direct influence of segmental mechanisms on the trigger point sensitivity at the infraspinatus site (PPTseg). Test subjects demonstrated statistically significant increases in Total Allodynia scores and significant decreases in PPTseg at 10, 20, and 30 minutes after application, when compared with control subjects. These results demonstrate that increases in central sensitization evoke increases in trigger point pressure sensitivity in segmentally related muscles.

Perspective: Myofascial pain is the most common form of musculoskeletal pain. Myofascial trigger points play an important role in the clinical manifestation of myofascial pain syndrome. Elucidating the role of central sensitization in the pathophysiology of trigger points is fundamental to developing optimal strategies in the management of myofascial pain syndrome.

David G. Simons (1922 – 2010) the authority to the study of myofascial pain, and the co-author of the famous Red Book :The Trigger Point Manual, the first definitive textbook on the diagnosis and management of trigger point, passed away on Easter Monday 5 April 2010.

Dr. Simons has an early career as the United States Air Force Flight Surgeon, and was chief scientist for Project Manhigh in the 1950s and piloted the program’s second flight to a record-setting altitude of 102,400 feet above sea level. Dr Simons met Dr. Janet Travell when she lectured about trigger points and myofascial pain at the Air Force’s School of Aerospace Medicine. Simons was so intrigued by Travell’s work that he eventually retired from the Air Force in 1965 and began a long informal apprenticeship under her wing.
His research in the diagnosis and treatment of myofascial pain led him to author more than 200 publications about trigger points and chronic pain management and became an internationally recognized authority on the subject.

In his paper in 1996, “Clinical and Etiological Update of Myofascial Pain from Trigger Points”, he concluded that: “Myofascial TrPs are a common cause of musculoskeletal pain.”

Dr. Simons never fully retired. At the time of his death, he was living in Covington, Georgia, USA, and was a Professor at Emory University and an Adjunct Professor at the University of Saint Augustine. He was also fully engaged in the latest revision of The Trigger Point Manual.

Based From: http://stratocat.com.ar/artics/simons-e.htm

OBJECTIVES: Low-intensity low-frequency electrostimulation delivered within a myofascial trigger point (MTP) has been used as intervention to deactivate MTPs. The therapeutic effect has been suggested to be due to peripheral mechanisms. However, nonpainful stimuli are also known to reduce simultaneous pain through central effects. The primary objective of the present study was to assess if central pain modulation occurs after intervention with low-intensity electrostimulation within an MTP. We hypothesized that intervention induces pain inhibition via the periaqueductal gray (PAG).

METHODS: Twenty-four patients with myofascial pain syndrome participated in the study. During functional magnetic resonance scanning, painful (high-intensity) intramuscular electrostimulation was delivered at random intervals (mean interstimulus interval=10.2 s) within an MTP of the upper left trapezius muscle. In-between scanning sessions, intervention (intramuscular electrostimulation, low-intensity, interstimulus interval=0.5 s) was applied to the same area. Patients were divided into responders and nonresponders according to their change in pressure pain thresholds relative to intervention. In addition to a whole brain search, a region of interest approach was also implemented to test the effect of intervention on PAG signal change.

RESULTS: The main findings were:
(1) intervention modulated PAG activity to painful stimuli more in responders than in nonresponders,
(2) change in PAG activity from the whole patient population correlated with change in pressure pain threshold, and
(3) a network known to regulate affective qualities of the pain experience was (subsignificantly) engaged more in responders than in nonresponders.

DISCUSSION: The applied intervention most likely involves supraspinal pain control mechanisms related to both antinociception and regulation of pain affect.

The Clinical Journal of Pain: June 2007 – Volume 23 – Issue 5 – pp 440-448
Niddam, David M. PhD; Chan, Rai-Chi MD; Lee, Si-Huei MD; Yeh, Tzu-Chen MD, PhD; Hsieh, Jen-Chuen MD, PhD

Excessive yawning induced by stimulation of myofascial trigger point – case report
C.-C. Chang and S.-T. Chang
Department of Physical Medicine and Rehabilitation, Tri-Service General Hospital, School of Medicine, National Defense Medical Center, Taipei, Taiwan

We describe a 44-year-old female patient with unusually severe muscle tightness in upper trapezius, levator scapulae, scalenes and the suboccipital extensors pain, which are ascribable to subcutaneous posterior cervical and thoracic trigger points. She was referred to our department for further rehabilitation therapy because of the muscle pain, which was in accordance with marked hyperesthesia, but without referred (distant) pain. She had no history of hypertension, diabetes mellitus, dyslipidemia or cardiac arrhythmia. There were no specific illnesses in her family background. Results of all laboratory tests were within normal limits. A possible contribution might come from the preexisting degenerative change of cervical spine found on the plain films. Maneuver of self-myofascial release (SMR) together with stretching exercise learned from our therapist was used to improve myofascial restrictions and to restore soft-tissue extensibility. Interestingly, several days later, excessive yawning developed whenever she was performing SMR in our physiotherapy room .

Myofascial pain syndrome (MPS), a kind of non-articular musculoskeletal problem, is a painful condition associated with regional pain and muscle tenderness depicted by the presence of myofascial trigger points (MTPs) with hypersensitive nodules. The signs and symptoms associated with MPS include taut muscular bands, palpable nodules, pain are exacerbated by stress and referred pain patterns [1]. There has been no consensus to diagnose the criteria of MPS, but it is commonly agreed that pain is a significant manifestation arising from MTPs [2]. MTPs are manifested as focal muscle contracture on which pressure induces pain and twitching responses [1].
With regard to the treatment of MTPs, the therapeutic effect on the muscle contractions has been suggested to be due to stretch and relaxation of the involved deep muscle fibers possibly resolving the local ischemia postulated as underlying cause of the pain [3]. Considering another treatment, the SMR is a technique used to mitigate myofascial restrictions and restore the extensible structure of soft-tissue [4]. Niddam et al. have recently provided evidence that the intervention of MTP at least partially involves supraspinal pain control via midbrain periaquaduct gray (PAG) [5]. In addition, van der Plas et al. suggested the PAG involving in the hypotensive pathway can be activated by the electrical stimulation of hypothalamic areas [6].
The above points of view imply that the central modulation of pain evoked from MTP might be connected to excessive yawning via spinothalamic tract, PAG and hypothalamus. Regarding the relationship between excessive yawning and thermoregulation [7], excessive yawning has been noted as a symptom of abnormal thermoregulation influenced by hypothalamus [8]. However, further research should be performed to identify the possible connection between specific thermal responsiveness of ventromedial hypothalamic neurons and yawning induced by the stimulation of MTPs in addition to the nonthermal-related excessive yawning [9].

European Journal of Neurology
Volume 16, Issue 6, Pages e118-e119

Acupuncture and dry needling in the management of myofascial trigger point pain: A systematic review and meta-analysis of randomised controlled trials
Tough, E.A., White, A.R., Cummings, T.M., Richards, S.H., Campbell, J.L.     2009     European Journal of Pain 13 (1), pp. 3-10     0

Pain from myofascial trigger points is often treated by needling, with or without injection, although evidence is inconclusive on whether this is effective. We aimed to review the current evidence on needling without injection, by conducting a systematic literature review. We searched electronic databases to identify relevant randomised controlled trials, and included studies where at least one group were treated by needling directly into the myofascial trigger points, and where the control was either no treatment, or usual care; indirect local dry needling or some form of placebo intervention. We extracted data on pain, using VAS scores as the standard.

Seven studies were included. One study concluded that direct dry needling was superior to no intervention. Two studies, comparing direct dry needling to needling elsewhere in the muscle, produced contradictory results. Four studies used a placebo control and were included in a meta-analysis. Combining these studies (n = 134), needling was not found to be significantly superior to placebo (standardised mean difference, 14.9 [95%CI, -5.81 to 33.99]), however marked statistical heterogeneity was present (I2 = 88%). In conclusion, there is limited evidence deriving from one study that deep needling directly into myofascial trigger points has an overall treatment effect when compared with standardised care.

Whilst the result of the meta-analysis of needling compared with placebo controls does not attain statistically significant, the overall direction could be compatible with a treatment effect of dry needling on myofascial trigger point pain. However, the limited sample size and poor quality of these studies highlights and supports the need for large scale, good quality placebo controlled trials in this area.