Background
- Myofascial pain syndrome (MPS) is a common cause of chronic musculoskeletal pain, with myofascial trigger points (MTrPs) being central to this condition.
- MTrPs are hypersensitive nodules in skeletal muscle associated with pain, muscle stiffness, and other symptoms.
- Manual palpation to identify MTrPs relies on subjective physical examination and has been found to have poor inter-rater reliability, highlighting the need for more objective characterization.
Methods
- This was a systematic review examining the use of imaging techniques such as ultrasound, MRI, and infrared thermography to quantitatively assess MTrPs.
- The authors searched multiple databases for relevant studies published from 2000-2021 and screened abstracts, conducted full text review, and extracted data on study methods and findings.
Findings
- Imaging data indicates MTrPs are localized regions of increased muscle stiffness compared to surrounding tissue.
- Ultrasound-based techniques like elastography appear most promising in distinguishing between clinically relevant groups and identifying MTrPs.
- Doppler ultrasound shows MTrPs have altered blood flow patterns. MRI and thermography also demonstrate ability to detect MTrPs.
Discussion
- Imaging modalities show potential for objective characterization of MTrPs but more research is needed on diagnostic accuracy and reproducibility.
- Due to factors like cost, ease of use, and availability, ultrasound seems to currently be the modality of choice for MTrP assessment in clinical practice.
- Studies showed some inconsistencies and limitations including heterogeneity in methods and populations.
- More research could help elucidate mechanisms and lead to targeted therapies for MPS.
What are the most promising imaging techniques for objective characterization of myofascial trigger points (MTrPs)? Why does ultrasound seem to currently be the modality of choice?
Based on the findings of this review, ultrasound-based techniques, especially elastography methods, appear to be the most promising for quantitatively assessing MTrPs. Multiple studies utilizing vibration sonoelastography, shear wave elastography, and compression elastography were able to reliably detect differences in tissue stiffness between active MTrPs and surrounding muscle or healthy controls. Elastography techniques directly measure mechanical properties and avoid limitations of grey-scale analysis for tissue characterization. Other advanced ultrasound techniques like Doppler imaging also showed promise in detecting altered blood flow patterns in MTrPs.
Compared to other modalities, ultrasound is currently the imaging method of choice due to its relative low cost, ease of use, real-time capabilities, and wide availability in clinical settings. Ultrasound elastography techniques can be implemented on conventional scanners with software upgrades, making adoption more feasible. MRI and thermography, while shown to detect MTrPs, have limitations in terms of high cost, long scan times, accessibility, and thermography’s indirect nature.
How consistent and reproducible are the findings on increased muscle stiffness in MTrPs across different studies and imaging modalities? Could this lead to quantitative imaging biomarkers?
The review found a high level of agreement in quantitative stiffness values of MTrPs across studies using different techniques. For example, the elastic modulus of MTrPs measured 12-14 kPa on ultrasound elastography, compared to 5-8 kPa in normal muscle. Shear wave speeds were consistently higher in MTrP regions at 2-5 m/s. MRI elastography also corroborated increased stiffness, measuring taut bands at around 11 kPa[1]Valera-Calero JA, Sánchez-Jorge S, Buffet-García J, Varol U, Gallego-Sendarrubias GM, Álvarez-González J. Is shear-wave elastography a clinical severity indicator of myofascial pain syndrome? An … Continue reading.
The consistent, reproducible findings of increased stiffness support the reliability of these imaging methods for tissue characterization and their potential for development as quantitative imaging biomarkers. Threshold values and cut-offs for diagnosis will need to be established through larger scale studies on diagnostic accuracy. Reproducibility also needs to be proven across different equipment, operators, and populations. But with further validation, quantitative measures of tissue mechanics hold promise as biomarkers for standardized MTrP assessment.
What is needed to translate these imaging research methods into more widespread clinical adoption and use for MTrP assessment? What are the barriers?
Several needs must be addressed to facilitate broader clinical adoption of imaging for MTrP assessment:
- Larger multicenter studies proving diagnostic accuracy, sensitivity/specificity, and reproducibility in varied settings
- Consensus guidelines on optimal protocols and quantitative stiffness measures for standardization
- Cost-effectiveness data and studies in broader patient populations to demonstrate value
- Integration of turnkey imaging packages/presets on commercial ultrasound scanners
- Training programs and accreditation for proper technique, imaging interpretation
- Increased availability and affordability of elastography-enabled ultrasound systems
Barriers include high equipment costs, lack of reimbursement and clinical time constraints, need for specialized expertise in image acquisition and interpretation, and difficulty of scanning certain anatomies. Ultimately, clear evidence proving added value over palpation alone will be key for changing practice.
Can imaging provide insights into the underlying mechanisms and etiology of MTrPs and myofascial pain syndrome? Could molecular imaging techniques like PET play a future role?
By quantifying altered muscle tissue stiffness and blood flow, imaging provides objective evidence supporting current theories on the etiology of MTrPs, such as localized muscle contractures and ischemia. Doppler ultrasound findings of vasoconstriction and high systolic velocities align with hypothesized inflammation and dysfunctional motor endplate activity.
Looking forward, molecular imaging techniques like PET could be used with targeted radiotracers to directly visualize pathological processes, receptors, and neurotransmitters implicated in MTrPs. If specific molecules involved in pain, inflammation, neuromuscular dysfunction, or other processes can be identified, PET and other molecular imaging approaches could provide unprecedented insights into the underlying mechanisms and pathophysiology. This could greatly aid etiological understanding and development of treatments.
Are there important gaps in the current literature on imaging of MTrPs? What patient populations, anatomical locations, and comparison groups need to be better studied?
Several evidence gaps exist, including:
- Lack of diagnostic accuracy studies: Very few studies evaluated sensitivity/specificity of imaging for MTrP diagnosis compared to clinical examination. More data is needed on test performance.
- Limited populations studied: Most studies had small sample sizes and recruited patients already diagnosed with myofascial pain. Evaluation in broader populations at risk is needed.
- Narrow anatomical focus: The majority of studies imaged the trapezius and shoulder muscles. More data on other common sites like lower back is needed.
- Variable comparator groups: Studies used a mix of comparisons including contralateral sides, surrounding muscle, separate healthy controls. Standardization would benefit the field.
- Underrepresentation of males: Many studies had predominantly or exclusively female patients. Sex differences need to be explored.
- Scarce long-term data: The natural history of MTrPs over time and their response to treatments has been scarcely studied via imaging.
How can imaging be used to improve diagnosis and characterize subtypes of myofascial pain syndrome? Can imaging distinguish active vs latent MTrPs better than palpation?
Imaging could enhance myofascial pain diagnosis by:
- Allowing earlier detection of MTrPs before palpable findings emerge
- Distinguishing cases from normalcy or mimics with standardized quantitative metrics
- Identifying affected muscles not readily palpated, like deep paraspinal muscles
- Supporting clinical suspicion when physical examination is equivocal
- Confirming presence and number of MTrPs when palpation is unreliable
Some imaging features like vascularity may differentiate active, symptomatic MTrPs from latent ones better than palpation by capturing underlying pathophysiologic variations. However, more research is needed to define distinguishing imaging criteria for subtypes.
What role could imaging play in selecting appropriate patients for specific treatments and objectively evaluating therapeutic responses over time?
Imaging could:
- Quantify severity at baseline to guide treatment aggressiveness
- Assess number/locations of MTrPs to target with focused interventions
- Determine subtype (active vs latent) to select appropriate therapy
- Identify patients unlikely to benefit from certain treatments
- Provide early marker of treatment response versus non-response
- Quantify changes in stiffness, size, blood flow after treatment
- Confirm therapeutic effects on precise trigger points treated
- Uncover undiagnosed MTrPs persisting after clinical improvement
Repeated imaging could thus optimize therapy and objectively demonstrate therapeutic efficacy.
How do sex differences and other demographic factors influence the presentation and imaging appearance of MTrPs?
This review highlighted the scarcity of data on sex differences given underrepresentation of males in most studies. Females have a higher prevalence of chronic pain conditions including myofascial pain. Gender likely influences risk factors, clinical presentation, and treatment responses.
Imaging studies are needed to determine if MTrP stiffness, size, location, etiology, or therapeutic responsiveness differ between sexes when accounting for factors like age, activity levels, and comorbidities. Understanding differences could allow more personalized diagnosis and management.
Other factors like age, genetics, psychosocial elements, and behavioral habits may also impact MTrP characteristics and imaging findings. Overall, the influence of demographic variables remains an important unanswered question in the field.
What future directions are needed in imaging research to better understand MTrPs and improve clinical management of patients with myofascial pain?
Key areas for future imaging research include:
- Conducting large multi-center trials to establish diagnostic accuracy and clinical value
- Standardizing protocols and developing quantitative imaging biomarkers
- Elucidating the natural history of MTrPs over time using longitudinal imaging
- Employing imaging to predict and assess response to various therapies
- Using advanced techniques like ultrasound elastography and MRI to distinguish MTrP subtypes
- Correlating imaging features with patient-reported outcomes and disability
- Evaluating role of imaging in guiding minimally invasive interventions
- Assessing MTrPs in understudied populations such as children, elderly, minorities
- Combining imaging with other modalities like electromyography to obtain complementary data
- Developing 3D and 4D ultrasonography methods for enhanced visualization
- Harnessing machine/deep learning algorithms to automate analysis and interpretation
How can imaging be integrated with other emerging techniques like biomarkers and genomics to get a fuller picture of myofascial pain mechanisms?
A multiparametric approach combining imaging with biochemical biomarkers, genomics, and other omics data could provide a comprehensive systems-level understanding of myofascial pain.
Examples of integrative techniques include:
- Imaging tissue stiffness along with profiling inflammatory markers or neuropeptides locally in the milieu of MTrPs.
- Correlating specific genomic polymorphisms to variations in MTrP size, stiffness, and symptomology on imaging.
- Using PET/MRI to concurrently visualize molecular pathological processes and tissue morphology in MTrPs.
- Analyzing the microbiome or proteome from MTrP regions and integrating with imaging phenotypes.
- Applying radiomics approaches to extract quantitative imaging features reflecting genomic and proteomic patterns.
By integrating imaging with various novel molecular techniques, researchers can form a deeper understanding of the biological underpinnings and mechanisms of myofascial pain on a personalized basis. This could ultimately lead to more targeted and individualized therapies.
MD, PhD. Physical Medicine & Rehabilitation Physician from São Paulo - Brazil. Pain Fellowship in University of São Paulo.
References
| ↑1 | Valera-Calero JA, Sánchez-Jorge S, Buffet-García J, Varol U, Gallego-Sendarrubias GM, Álvarez-González J. Is shear-wave elastography a clinical severity indicator of myofascial pain syndrome? An observational study. Journal of Clinical Medicine. 2021 Jun 29;10(13):2895. |
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