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14 Articles in Volume 12, Issue #2
Chronic Pain in the Elderly: Special Challenges
Chronic Pain School
Diagnosis and Management Of Myofascial Pain Syndrome
ECG Screening Prior to Initiating Methadone: Is it Really Necessary?
HCG and Testosterone
How to Manage Unmotivated Pain Patients
March 2012 Pain Research Updates
Methadone for Pain Management
PPM Editorial Board Discusses Methadone Prescription Safety Measures
PPM Launches Online Opioid Calculator
Spontaneous Low Back Pain, Radiculopathy, And Weakness in a 28-Year-Old
Tapering a Patient Off Opioids
The Comorbidity of Chronic Pain and Mental Health Disorders: How to Manage Both
What Are Best Safety Practices For Use of Methadone In the Treatment Of Pain?

Diagnosis and Management Of Myofascial Pain Syndrome

Investigating—and eliminating—the underlying causes of active trigger points is key for clinicians to effectively manage patients with myofascial pain syndrome, a common cause of chronic musculoskeletal pain.

Myofascial pain syndrome (MPS) is a common musculoskeletal disorder caused by myofascial trigger points.This painful disorder can affect any of the skeletal muscles in the body and the prevalence varies by medical specialty—it accounts for 21% of orthopedic clinic visits, 30% of general medicine visits, and approximately 85% to 93% of pain management clinic visits.2 MPS has become a major cause of time lost from work, resulting in a loss of millions of dollars from the economy.3

Etiology
The pathophysiology of MPS is not completely understood. It is currently hypothesized that trigger points, the most common feature of MPS, contain areas of sensitized low-threshold nociceptors (free nerve endings) with dysfunctional motor end plates. These motor end plates connect to a group of sensitized sensory neurons in charge of transmitting pain information from the spinal cord to the brain.3

The affected muscle with the trigger point is associated with motor dysfunction and usually contains a palpable taut band or nodularity within the muscle belly. The taut band is considered to be a sustained band of contracted muscle due to increased concentrations of acetylcholine (ACh)—a neurotransmitter—in the synaptic cleft, changes in the ACh receptor activity, and/or changes in acetylcholinesterase activity.4

Electrodiagnostic studies suggest that a pathologic increase in ACh contributes to an increase in motor end plate activity as well. This constant state of muscle contraction and hyperactivity of motor end plates can increase the amount of energy consumption and affect the delicate supply and demand of nutrients and oxygen to the affected muscle. The high demand of resources needed by the affected muscle can eventually lead to hypoperfusion, ischemia, hypoxia, and finally, muscle damage.2 Localized muscle ischemia and muscle damage can trigger the release of neurovasoreactive substances such as prostaglandins, bradykinin, serotonin, adenosine triphosphate, potassium, and protons (H+), which can then activate the muscle nociceptors responsible for myofascial pain.4

Signs and Symptoms
Patients with MPS usually report regionalized aching, and diffuse, persistent pain in certain muscles and joints. The pain intensity can vary from mild to severe and is usually related to muscle activity. Patients may even have a history of dropping things due to pain-induced muscle weakness.3 Symptoms may begin after trauma or injury to the affected area or can be of gradual onset.2 The most commonly affected areas are the muscles in the neck and shoulders (ie, trapezius, scalene, and sternocleidomastoid muscles) and pelvic girdle.1

Trigger points, one of the main characteristics of MPS, are considered to be hyperirritable, circumscribed spots located in a palpable taut band of skeletal muscle (Table).5 These points are painful on compression and can produce referred pain, referred tenderness, and even autonomic phenomena.1 Referred pain and tenderness occur when pain is referred to remote sites from compression of a myofascial trigger point.5 For example, pain from compression of trigger points in the scalene muscles of the neck may be felt in the hand. Myofascial trigger points of different muscles are associated with their own characteristic pain pattern; thus, the unique distribution of pain can help the clinician to correctly determine which muscles are affected by MPS.2

Myofascial trigger points are different than the tender points found in fibromyalgia, in which pain occurs only at the site of palpation and is commonly associated with fatigue and sleep disturbances. Associated autonomic phenomena such as sweating, abnormal tearing, abnormal salivation, increased vasomotor response, and increased pilomotor response, can also potentially occur in extreme cases of MPS. It is believed that an autonomic phenomenon is a result of multiple sensitive nociceptors located in the region of trigger points. Nociceptors are activated upon compression of a trigger point, which can potentially overstimulate sensory neurons.5 Other associated neurologic symptoms include paresthesias, numbness, blurred vision, trembling, dizziness, and tinnitus.2

MPS trigger points can be classified as active or latent depending on their clinical characteristics. An active trigger point causes spontaneous pain and is tender to palpation with referred radiating pain.1 Latent trigger points are tender but not spontaneously painful. They usually are found in asymptomatic patients and can cause stiffness and limit range of motion (ROM).A number of studies suggest that latent trigger points can be commonly found in the shoulder-girdle muscles of 45% to 55% of asymptomatic young adults.2 Latent trigger points can be a result of active trigger points that have been suppressed with treatment.5 They also can develop into active trigger points as a result of psychological stress, muscle tension, and physical factors such as poor posture.

Another classic sign of MPS includes visible or palpable local twitch responses (LTRs) in the affected muscle. LTRs are brisk contractions of the muscle fibers within or around the taut band. Additionally, limitation of movement and, initially, muscle weakness without atrophy can be seen in patients.The pain induced by engaging the affected muscle is the underlying cause of limited ROM and reduced muscle strength. The prolonged muscle inactivity can then, eventually, lead to muscle atrophy.5

Diagnosis
A thorough physical examination for MPS should entail a meticulous neurologic and musculoskeletal examination. Upon examination, a trigger point can be located by palpating a firm, hypersensitive nodule that elicits radiating pain when local pressure is applied to it.1 The referred pain also can be associated with sensory disturbances such as parasthesias, dysesthesia, and localized extreme skin tenderness. Observations can be confirmed with electromyography (EMG). An active group of nociceptors in the tender nodules can show evidence of spontaneous electrical activity on EMG. Also, the clinician can further localize trigger points by noting lowered skin resistance to electrical current in these areas compared with the surrounding tissues.3

Currently, no laboratory test or imaging technique has been completely established for diagnosing trigger points for MPS. However, lab tests can be helpful in looking for predisposing conditions, such as vitamin deficiencies, hypothyroidism, and hypoglycemia. Trigger points are sometimes associated with an increase in blood flow, which can be detected by infrared or liquid crystal thermography. Other imaging studies are useful in order to rule out other causes of musculoskeletal pain. Ultrasonography with needle penetration also has been used to visualize LTRs associated with MPS.3

Management
Management of patients with MPS includes the elimination of chronic overuse or stress injury of affected muscles. A patient’s posture, biomechanics, and joint function should be analyzed carefully to identify any underlying factors that may have contributed to the development of myofascial pain. Treatment methods include physical therapy, osteopathic manual medicine, heat or ice modalities, the spray and stretch technique, dry needling, and trigger point injections (TPI) with local anesthetic, saline, or steroid.1 Other therapeutic adjuncts to nonpharmacologic or pharmacologic treatments include acupuncture, massage, transcutaneous electrical nerve stimulation, and ultrasound.2

Manual Techniques
The decision whether to treat trigger points by manual methods or by slightly more invasive procedures like injections depends on the training of the physician and severity of the trigger point pain. Manual methods and/or physical therapy are indicated for patients with new, acute trigger points, patients with a fear of needles, and/or trigger points not easily accessible by injection (ie, psoas muscle).1 Stretching exercises are the first line of treatment for patients because they focus on relieving muscle tightness and shortening related to myofascial pain.2 Physical therapy entails targeted stretching and strengthening of affected muscles and correcting improper postural factors.3 Manual methods, such as osteopathic manipulation, include specific techniques like myofascial release, counterstrain, muscle energy, and high-velocity/low-amplitude manipulation. All these osteopathic techniques aim to stretch and increase ROM of affected muscles. Once myofascial pain has been stabilized and ROM restored, all patients should be encouraged to continue a strengthening program with aerobic exercise to prevent future recurrence. An important feature of MPS treatment is educating patients about the effectiveness of manual techniques, which empowers patients to manage their own symptoms.

Spray and Stretch
One therapeutic option, the spray and stretch technique, involves the physician passively stretching the patient’s affected muscle while simultaneously spraying dichlorodifluoromethane/trichloromonofluoromethane or ethyl chloride topically. The spray produces a cooling sensation by causing an abrupt drop in skin temperature at the targeted area. This cooling sensation acts as a temporary anesthesia by blocking the spinal stretch reflex and the sensation of pain. The patient’s perception of decreased pain enables the physician to passively stretch the affected contracted muscles toward a normal length. Passively stretching the affected muscles helps inactivate trigger points and, therefore, decreases referred pain.1

Trigger Point Injections
In recent years, TPIs and dry needling of trigger points have become widely accepted as a result of their abilities to provide prompt symptomatic relief.However, patients are at risk for becoming dependent on injections for pain relief if used as the initial and primary treatment for MPS. When other noninvasive options have been exhausted, TPIs may then be necessary to manage chronic, persistent myofascial pain.2 Usually, three consecutive visits are recommended for chronic MPS cases, with reassessment of symptoms to determine if further injections are needed.2 The efficacy of injections can be attributed to precisely locating the site of maximal pain within the trigger point and eliciting an LTR upon insertion of the needle. Studies have shown that eliciting an LTR during the injection has been associated with immediate relief of pain and muscle tightness.For deep muscles, ultrasound-guided trigger point injections can be utilized to identify LTRs that were not detected by using visual assessment and have been associated with better outcomes in management of pain.6

Injections may involve several medications or no medication at all (dry needling). Some of the medications include anesthetics like bupivacaine, etidocaine, lidocaine, and saline or sterile water.3 Additionally, areas associated with increased inflammation can be treated with steroids. Lately, botulinum toxin (Botox) has been considered for the treatment of MPS due to its potential to provide long-lasting relief to patients. Botulinum toxin can relieve taut bands and trigger points in affected muscles by blocking ACh.5 The decrease in ACh concentrations at neuromuscular junctions reduces muscular contractions and hyperactivity, which in turn can improve local ischemia.2 Best long-term results are obtained when injections are followed by manual stretching techniques and patient compliance with a home stretching program. Increase in pain relief can enable muscle function, normal muscle activity, and further inactivate other myofascial trigger points.2

Dry Needling
Dry needling involves placement of needles without any substance and has been proven to be as effective as injecting with medication. The proposed mechanism of pain relief by needle stimulation is due to hyperstimulation analgesia. Insertion of a dry needle applies strong pressure to sensitized nociceptors in the target area. These nociceptors then provide strong neural impulses to sensory neurons in the spinal cord, which might interrupt the trigger point pain circuit.5 However, dry needling is less commonly used because prolonged post-injection soreness has been reported by patients compared with those injected with lidocaine.1

Following TPIs, patients are advised to avoid strenuous activity for the first few days, but are encouraged to remain active and engage their muscles through their full ROM. If two to three injections are shown to be ineffective, then reinjection should be avoided.5

The complications associated with TPIs are rare and depend on the location of the injection. Some of the risks include local pain, bruising, bleeding, infection, and intramuscular hematoma formation. Neural vascular injury or penetration of an organ is found to be extremely rare.3

Patients with MPS also can be treated with nonsteroidal anti-inflammatory drugs and/or muscle relaxants. However, these medications only provide symptomatic relief and usually are effective when used in conjunction with active, exercise-based manual/physical treatment of MPS.3

Conclusion
MPS is an extremely common cause of chronic musculoskeletal pain in the United States. In patients with MPS, clinicians should always investigate the underlying reason for active trigger points. Treatment should be based on eliminating the underlying cause and should be started conservatively with manual therapy and then a gradual introduction of other modalities like TPIs, if pain persists. Patients should be re-evaluated periodically until all symptoms have resolved or stabilized. MPS is a musculoskeletal disorder that should not be taken lightly because, over time, the pain can decrease patient quality of life. Also, as chronicity increases, symptomatic relief from treatment can become quite difficult to manage. The best prognosis for the resolution of MPS is beginning treatment early and eliminating aggravating factors as soon as possible.

Last updated on: March 19, 2012
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