Myofascial pain syndrome (MPS) is characterized by single or multiple trigger points (TrP) in taut bands within the affected muscles. Chronic MPS over neck is prevalent and responsible for markedly loss of work-day and a reduction of quality of life.

Intravascular laser irradiation of blood (ILIB) involves in vivo illumination of the blood by low-level laser light through an optical fiber inserted in a vein. Researches disclosed that ILIB reduced blood viscosity, enhanced erythrocyte deformity, and increased oxygen saturation in blood. However, no research studies the effectiveness of ILIB to treat MPS.

Real-time sonoelastography (RTS) and shear wave velocity (SWV) are used to detect the stiffness of skeletal muscles. RTS is displayed as a color-coded graphic to represent the relative stiffness of structures. For a given material, faster SWV indicates the greater stiffness. To our knowledge, only one research using RTS and SWV to study MPS.

To elucidate the effectiveness of ILIB to treat chronic MPS over neck, and the validity of RTS and SWV for MPS, we conducted this study.

1. Time interval of the study: from 2014-11-1 to 2016-10-31 2. Participants and sample size:

1. Participants: Patients having chronic MPS over neck were randomized allocated to experimental group or control group. Participants in both groups are evaluated before and after the interventions (week 0 and week 2 respectively), and 12 week after the intervention (week 14). Both participants and evaluators don't know the allocation.
2. Sample size: thirty-six participants. The investigators plan to recruit 18 participants in each year.

III. Intervention:

Participants in experimental group receive ILIB (He-Ne laser, wavelength 632.8nm) with output power 0.3mW for 60minutes and following transcutaneous electric nerve stimulation (TENS) and stretching exercise every day except weekend for 2 weeks. Participants in control group receive sham therapies with the same protocol but no laser energy output

IV.Outcome Measures:

1.Primary outcome: Pain as measured by using a 10-cm long visual analogue scale (0 indicates no pain while 10 indicates worst pain) at rest and at movement.

2.Secondary outcomes:

1. .Pressure pain threshold (PPT) as measured by a pressure algometer, Force Dial FDK 20 with a scale ranging from 0 to 10 kg (Wagner Instruments, Greenwich, USA). The participant is in sitting position and relaxes, and the most painful TrPs in the taut band is measured. The investigators follow the procedures of measurement described by Fischer. The PPT is defined as the minimal pressure that results in the sensation change from pressure to pain. The investigators perform 3 repetitive measurements at an interval of 20 seconds, and the mean values will be analyzed.
2. .Shear wave velocity (SWV): SWV is undertaken by a physiatrist specialized in musculoskeletal US using a US system with 4-9 MHz multifrequency linear transducer (S2000; Siemens Healthcare, Erlangen, Germany). The posture of participant is the same with which when testing PPT. The investigators minimize probe pressure on muscles to avoid affect muscle stiffness. SWV of bilateral upper trapezius (TPZ), levator scapulae (LS), sternocleidomastoid (SCM) and the most painful TrP in taut band are measured longitudinally while their B-mode image qualities are optimal. When measuring TPZ, the probe was located at the midpoint of occipital protuberance and acromion and the ROI was placed inside the muscle belly. The SWV of LS is measured at the midpoint of superior-medial border of scapulae and the C1 transverse process. For the measurement of SCM, the probe is positioned at the midpoint of sternum and mastoid process. The most painful TrP in taut band is recognized by the participants and then marked and recorded its position related to bony landmarks with a measuring tape. SWV of each muscle is measured 10 times, and the median of the 10 valid measurements will be analyzed.
3. .Real-time sonoelastography (RTS): RTS is accessed by the aforementioned physiatrist by using the US system. RTS is depicted on the right side of the screen, while the longitudinal 2D image on the most painful TrP in taut band is displayed on the left side. The compression force applied is adjusted according to a quality factor set on the machine, which is displayed on the screen. A quality factor ≧ 60 indicates optimal compression force. The investigator stores the representative image with a quality factor ≧ 60, and determines the RTS score. Later, the stored images are analyzed with ImageJ software (National Institutes of Health,Bethesda, USA). The area of taut band on image is selected, and color histograms are made and the means of the blue pixel and the red pixel are recorded. The color pixels range from 0 to 255. Intrarater and interrater reliability tests for RTS and SWV are undertaken in the first 10 participants.
4. . World Health Organization Quality of Life Questionnaire Short Form (WHOQOL - BREF) Taiwan Version: WHOQOL - BREF Taiwan Version consists of 4 domains (physical health, psychological, social relationship, and environment) and a total 28 items. Each item has a five-point Likert-type response scale, and four types of scale descriptors (capacity, frequency, intensity and evaluation) are used.37 Individual domain score and total QOL score can be calculated through straightforward summative scaling. A higher score indicates a better QOL. This questionnaire was proved to be reliable and valid for many diseases.

V. Analysis and Statistics: Reliability of RTS and SWV are tested by using intraclass correlation coefficients. Within-group and between-group comparisons are made by using a repeated-measure ANOVA. Correlation coefficients among outcomes are calculated.

Inclusion Criteria:

• (1) age ≧ 18 years old; (2) willing to sign an inform consent; (3) having a chronic MPS over neck at least 6 months. The diagnosis of MPS was made while the following criteria are met: (a) recognized pain with exquisite spot tenderness on a palpable taut band over the pain area; (b) presence of one of the two confirmatory signs: referred pain and local twitch response

Exclusion Criteria:

• (1) pregnancy; (2) bleeding tendency; (3) active systemic infective or inflammatory disease; (4) major surgery or trauma in the recent 3 months; (5) unstable cervical spine; (6) rheumatoid arthritis34; (7) open wound over neck; (8) pace-maker or defibrillator implantation; (9) overt neuropathic pain or radiation pain; (10) inability to express pain or quality of life.