Unraveling the Mysteries of Myofascial Pain Syndromes
There are few syndromes in musculoskeletal medicine that elicit more controversy and debate than what some authors have termed “functional syndromes” or myofascial pain syndromes (MPS) perhaps because little is known, understood, or agreed upon regarding these conditions. As recently as 2008, an article appeared in a prestigious journal which summarized the available literature on the reliability of manual palpation in the detection of myofascial trigger points ( a key feature of MPS) and concluded that existing methods of identifying TPs is generally poor and, as such, clinicians are urged toward “simpler and more global assessments of patient status.”1 It is not unusual to find this type of report in the literature which helps explain the difference in opinion within the clinical community in regards to the existence of entities such as trigger points.
To date, there are no gold standard imaging or electrophysiologic tests, or even clear universally accepted diagnostic criteria, for many of these syndromes. Without clear diagnostic criteria, practitioners are left with treating a cluster of symptoms guided primarily by patient symptoms or self-report. In the absence of a clear pathology, patient complaints of pain can be attributed by the treating physician as motivated by “other” factors such as: drug seeking behavior, malingering, or simply anxiety-mediated neurosis having no somatic origin.
Conditions such as fibromyalgia, poly-arthralgia, and myofascial dysfunction are at the top of the list of these mystery diagnoses. Clinicians become frustrated when confronted with a patient complaining of diffuse, non-specific joint and muscle discomfort and having no apparent etiology or causative agent that can readily be identified. Moreover, the symptom pattern can change on an almost daily basis and can be modified by such factors as weather changes, sleep, and activity patterns. The current array of imaging tests such as conventional MRI, CT, PET, radiography or ultrasound, have aided little in elucidating the etiology—or even the existence—of MPS. The same can be said about conventional lab testing, with no bio-chemical markers being identified as reliable indicators for the presence or absence of MPS.
Magnetic Resonance Elastography (MRE)
MRE is a relatively new diagnostic test to enter the imaging arena and promises to be a potentially useful test to verify the existence of such entities as taut bands in muscles and trigger points, both of which are hallmark components of myofascial disorders and have been elusive in diagnosing accurately. It is estimated that well over 9 million people—both men and women—in the US suffer with MPS, a condition marked by widespread pain and tenderness in the trunk and extremities. MRE seeks to identify changes in muscle tone and stiffness or elasticity, and so is based on measurement of the mechanical characteristics of soft tissue.2 Abnormal changes in soft tissue such as is seen in many cancers, various masses/tumors (consolidation), mineralizing disorders (calcification), or simply in tight and sore muscles can now be identified and characterized by MRE. Malignancies tend to be much harder than normal tissues and benign tumors. This is especially evident in breast cancer tumors which are most often detected by physical examination on the basis of hardness followed by tissue biopsy.3
The use of this technology has not been limited to soft tissue diagnosis but includes using the same bio-physical principles to detect lesions in liver, breast, brain and cardiac tissue with studies currently underway investigating all these applications.4 It is thought that in the near future the use of MRE will increase significantly—especially for monitoring muscle stiffness related to muscle-wasting diseases such as multiple sclerosis and hyperthyroidism.5
The underlying premise of MRE is that normal or healthy tissue has a certain shear modulus or elasticity whose values fall within a specific range. It also appears that different muscles have different elasticity ranges with modifying factors being tissue temperature, muscle size, and age of muscle being tested.6 The implications of using MRE are significant, with the obvious one being that, to date, tissue palpation of superficial tissue is a useful and reliable method of tissue examination, but limited by what the physician can feel under his/her hand. Using MRE will allow greater depth of visualization and assessment by the examiner using magnetic resonance technology to aid in this process.
The use of existing MR technology has been instrumental in the development of MRE with this newest MR application being based on harmonic mechanical excitation in which an acoustic or sound wave is created and propogated within the target tissue. This shear wave, along with some of the key features such as wavelength, is measured and quantified for correlation to skeletal muscle using both relaxed and contracted muscle states. It is now understood that shear wavelength increases with increasing tissue stiffness and increasing tissue tension levels.7 Most recently, MRE has validated an existing mathematical model of human skeletal muscle behavior in the biceps brachii, correlated to EMG data in the distal leg muscles, and quantified the effects of pathologies on the distal and proximal leg muscles.8
MRE and Specific Muscle Applications
The news about MR application using elastography has not come soon enough for those practitioners who have specialized in the diagnosis and treatment of soft tissue dysfunctions, nor for the millions of persons who suffer with tight, sore, and tender soft tissue structures such as tendons, ligaments, connective tissue, and muscle. Fibromyalgic symptoms (pain, point tenderness, tightness) are a feature of several controversial pathologic entities and may also include taut bands and trigger points (TPs) as components of these syndromes. Physicians, physical therapists, massage therapists, chiropractors, and others have been identifying muscle banding and TPs during routine palpation of involved muscles in patients for many years. Until now, there has been no method of precisely characterizing these entities in superficial anatomical structures. It was simply a matter of whether a TP was present or not. Palpation of deep anatomical structures, however, is uncomfortable to the patient and notoriously unreliable as a method of assessment of banding and TPs.