Myofascial pain syndrome is an incredibly common and potentially overlooked cause of pain in patients presenting to the emergency department. It was found in up to 85 percent of patients in one U.S. pain clinic, with a lifetime prevalence also estimated at 85 percent. (Semin Neurol. 2016;36:469.)
Myofascial pain syndrome often mimics a variety of complaints encountered in the ED, but can be diagnosed at the bedside through the identification of myofascial trigger points—focal hyperirritable nodules that are palpable in the tight bands of a muscle, thought to be caused by muscle overload or stress. The International Association for the Study of Pain recognizes that myofascial pain syndrome is a common source of musculoskeletal pain, and similar recognition and routine intervention by emergency clinicians represent an important opportunity to limit costly resource overutilization while tailoring safe and effective analgesic therapy.
Diagnosis of myofascial pain syndrome and identification of myofascial trigger points are often clinical, but diagnostic modalities including electromyography (EMG) and ultrasound (US) can be utilized if needed or desired. Trigger points have an EMG signature termed spontaneous electrical activity or endplate noise, which is persistent, fast low-amplitude (950 UV or less) activity with less frequent high-amplitude discharges of approximately 600 UV. Trigger points appear on US as uniform, focal, hypoechoic regions indicating local changes in tissue echogenicity. (Arch Phys Med Rehabil. 2009;90:1829; http://bit.ly/32O12mY.)
Commonly found in the muscles surrounding the thoracic or cervical spine, trigger points are often identified in the trapezius, sternocleidomastoid, levator scapulae, and suboccipital musculature. They may, however, contribute to local or referred pain nearly anywhere in the body. Thermal imaging has been employed to demonstrate changes consistent with zones of relative ischemia.
Myofascial pain syndrome can be rapidly diagnosed at the bedside with reproduction of exquisite pain within a single taut band of muscle. Response to therapeutic intervention can confirm the diagnosis and treat the painful condition effectively. Myofascial pain syndrome responds to a range of analgesic options, including systemic NSAID therapy, muscle relaxants, and topical anesthetics. Trigger point injection is also an incredibly effective intervention, which, while underused, is easy and satisfying for the patient and physician.
Two meta-analyses have demonstrated that wet needling (lidocaine injections) and dry needling (using a solid-filament needle with or without electrical stimulation) are similarly effective for neck and shoulder myofascial pain without clear differences. (J Bodyw Mov Ther. 2014;18:390; Arch Phys Med Rehabil. 2015;96:944.) Insertion of a wet or dry needle into a trigger point is thought to induce muscle twitch at the site, stretching muscle fibers and relieving capillary constriction upon relaxation, which restore microcirculation. This reoxygenates the muscle at the site of the trigger point, breaking the positive feedback.
Local tissue trauma induced by needling and disruption of muscle fibers within the trigger point also induces focal recruitment of inflammatory mediators and endogenous opioids to trigger repair of the underlying nociceptive nidus. Consider, for example, one truly fascinating small trial that demonstrated reversal of trigger point effectiveness following naloxone administration, adding further credence to the presumed role of endogenous opioids in trigger point injection. (Pain. 1988;32:15.)
Trigger point injection is one of the simplest procedures an emergency physician is likely to encounter, and requires the microskills of intramuscular needle placement and injection with which we are all extremely familiar. Once a trigger point is identified, the overlying skin is cleaned with an alcohol swab. A needle is inserted into the muscle belly and, in the case of wet needling, 0.5 mL of local anesthetic administered. It's my practice to use a 22-gauge needle and to insert the needle at about 45 degrees. The needle itself should be sufficient to interrupt the nociceptive tangle and recruit endogenous mitigators, with the injectate contributing to the same while treating post-injection pain and tenderness.
Trigger point injection is easy, safe, and straightforward, though it would be disingenuous not to discuss its risks. Many case reports of pneumothorax following aggressive needle placement exist, as do reports of nerve damage, infection, and various other rare injuries to adjacent structures. Certainly, as with all procedures, the risk-benefit analysis should be considered, though broadly speaking, risk is minimal if you do due diligence. Ultrasound guidance can be used for further safety.
Myofascial pain syndrome is common, and it may be a frequent offender when patients present with acute or chronic pain to the emergency department. Easily diagnosed at the bedside and just as easily treated and dispositioned, such a syndrome represents an excellent opportunity for safe, effective, and satisfying definitive care. Using trigger point injections for myofascial pain syndrome is a procedure well within the abilities of any practicing emergency physician, and should find its way into every clinician's analgesic toolbox.
Dr. Pescatoreis the director of emergency medicine research for the Crozer-Keystone Health System in Chester, PA. He is also the host with Ali Raja, MD, of the podcast EMN Live, which focuses on hot topics in emergency medicine:http://bit.ly/EMNLive. Follow him on Twitter @Rick_Pescatore, and read his past columns athttp://bit.ly/EMN-Pescatore.