MYO-FASCIAL PAIN

Myofascial pain (MP) is a common, painful disorder that is responsible for many pain clinic visits. MP can affect any skeletal muscles in the body. Skeletal muscle accounts for approximately 50% of body weight, and approximately 400 muscles make up the body.

MP is responsible for many cases of chronic musculoskeletal pain.

MP can cause local or referred pain, tightness, tenderness, popping and clicking, stiffness and limitation of movement, autonomic phenomena, local twitch response (LTR) in the affected muscle, and muscle weakness without atrophy.

Trigger points (TrPs), which cause referred pain in characteristic areas for specific muscles, restricted range of motion (ROM), and a visible or palpable LTR to local stimulation, are classic signs of MP. Over 70% of TrPs correspond to acupuncture points used to treat pain.

An active TrP is an area that refers pain to a remote area in a defined pattern when local stimulation is applied. Satellite TrPs appear in response to a primary, active TrP and usually disappear after the primary TrP has been inactivated. Latent TrPs cause stiffness and limitation of ROM but no pain. Frequently, they are found in asymptomatic individuals.

Although MP and fibromyalgia have some overlapping features, they are separate entities; fibromyalgia is a widespread pain problem, not a regional condition caused by specific TrPs.

PATHOPHYSIOLOGY

A taut band in a muscle may be necessary as a precursor to the development of a trigger point (TrP). Taut bands are common in asymptomatic individuals, but patients with them are more likely to develop a TrP. A latent TrP can develop into an active TrP for a number of reasons. Psychological stress, muscle tension, and physical factors, such as poor posture, can cause a latent TrP to become active.

The pathophysiology of myofascial pain is not well understood. Current research supports sensitization of low-threshold, mechanosensitive afferents associated with dysfunctional motor endplates in the area of the TrPs projecting to sensitized dorsal horn neurons in the spinal cord. Pain referred from TrPs, as well as LTRs, may be mediated through the spinal cord after stimulation of a sensitive locus.

SEX

Myofascial pain is distributed equally between men and women.

AGE

Myofascial trigger points (TrPs) can be found in persons of all ages, even infants. The likelihood of developing active TrPs increases with age and activity level into the middle years.

Sedentary individuals are more prone to develop active TrPs than are individuals who exercise vigorously on a daily basis.

CLINICAL

HISTORY

Patients with myofascial pain usually report regionalized aching and poorly localized pain in the muscles and joints. They also may report sensory disturbances, such as numbness in a characteristic of distribution. The type of pain felt is characteristic of the muscle involved.

An acute onset may occur after a specific event or trauma (eg, moving quickly in an awkward position), while chronic pain may result from poor posture or overuse. Patients may note disturbed sleep.

Persons with cervical and periscapular myofascial pain may have difficulty finding a comfortable sleeping position. They may or may not be aware of muscle weakness in the affected muscles and may have a tendency to drop things.

PHYSICAL

A skilled examiner can provide accurate diagnosis of myofascial pain (MP). Unfortunately, most medical school and residency training programs do not adequately cover this common condition.

Locating trigger points (TrPs) is the most important part of the physical examination. TrPs tend to occur in characteristic locations in individual muscles.

When the TrP is located, the patient typically has a positive jump sign when local pressure is applied over the area; the jump sign should not be confused with an LTR. The jump sign simply means that the patient jumps from pain or discomfort in the area that has been palpated.

Apply a consistent amount of pressure to the area, because applying too much pressure can elicit pain in nearly all individuals. A pressure algometer (ie, pressure threshold meter) or palpatometer can be used to standardize the amount of pressure applied.

A taut band is found in the muscle, either by palpation or by needle penetration. It can be distinguished by palpating or by dragging the fingers perpendicular to the muscle fibers. A localized knot or a tight, ropy area is noted. Patients report that the area is extremely tender when palpated.

A localized flinching in the area of the muscle being palpated or an LTR may be noted in active TrPs, as well as in latent ones. Palpation or insertion of a needle into the TrP causes reproduction of the patient's pain and, frequently, sensory complaints.

Palpation of either an active or a latent TrP causes referred pain in a characteristic area for each muscle, a phenomenon described in the above-mentioned TrP manual.

Sensory disturbance (eg, paresthesias, dysesthesias, localized skin tenderness) may be noted in the same area where pain may be referred.

Autonomic phenomena also may be elicited (eg, sweating, piloerection, temperature changes).

Essential criteria for identifying an active or latent TrP include the following:

Palpable taut band if the muscle is accessible
Exquisite spot tenderness of a nodule in a taut band
Patient's recognition of current pain complaint by pressure on the tender nodule
Painful limit to full ROM stretch of the involved muscle

Confirmatory observations include the following:

Visual or tactile identification of an LTR
Imaging of an LTR induced by needle penetration of a tender nodule
Pain or altered sensation on compression of a tender nodule, in the distribution expected from a TrP in that muscle
Electromyographic demonstration of spontaneous electrical activity (SEA) that is characteristic of active loci in the tender nodule of a taut band
Lowered skin resistance to electrical current - This has been found over active TrPs when compared with surrounding tissue and may be useful in localizing TrPs. Skin resistance normalizes after the treatment of TrPs.

CAUSES

Several factors contribute to myofascial pain (MP).

Abnormal stresses on the muscles from sudden stress on shortened muscles, leg-length discrepancies, or skeletal asymmetry are thought to be common causes of MP.

Poor posture also may cause MP. In addition, the assumption of a static position for a prolonged period of time has been implicated in the condition.

Anemia and low levels of calcium, potassium, iron, and vitamins C, B-1, B-6, and B-12 are believed to play a role.

Chronic infections and sleep deprivation have been cited as causative factors, as have radiculopathy, visceral diseases, and depression.

Hypothyroidism, hyperuricemia, and hypoglycemia also have been implicated in MP. The pathogenesis likely has a central mechanism, with peripheral clinical manifestations.

DIAGNOSIS

LABORATORY STUDIES

No specific lab tests confirm a diagnosis of myofascial pain (MP), but lab tests can be helpful in looking for predisposing conditions, such as hypothyroidism, hypoglycemia, and vitamin deficiencies. Specific tests that may be helpful include complete blood count (CBC), chemistry profile, erythrocyte sedimentation rate (ESR), and levels of vitamins C, B-1, B-6, B-12, and folic acid. A thyrotropin level may be helpful if clinical features of thyroid disease are present.

IMAGING STUDIES

Infrared or liquid crystal thermography can show increased blood flow, which is sometimes noted at trigger points. Other imaging studies are useful only to rule out other sources of pain generation.

OTHER TESTS

Needle electromyography (EMG) examination of trigger points (TrPs) in humans and rabbits has shown high-voltage spike activity and spontaneous, low-voltage endplate noise, which is considered characteristic but not pathognomonic. Surface EMG has been used in experiment protocols to monitor muscle activity in TrPs. Ultrasonography has been used to visualize the LTR elicited by needle penetration.

PROCEDURES

Trigger point (TrP) injections sometimes are performed with bupivacaine, etidocaine, lidocaine, saline, or sterile water. Dry

needling is occasionally performed, without the injection of any substance.

Steroids may be used in areas possibly associated with inflammation, as in frozen shoulder. Botulinum toxin (BOTOX®) shows promise as a substance that can provide long-lasting relief. Its mechanism

of action may be related to the blocking of acetylcholine release at the neuromuscular junction of the dysfunctional motor endplates.

A report by Affaitati et al indicated that a topical anesthetic patch can also relieve myofascial pain, without the discomfort that can result from TrP injections. Patients in the study were separated into

groups of 20, one of which was treated for 4 days with a lidocaine patch applied to each patient's trigger point (with patients receiving a total daily dose of 350 mg). The second group received a placebo patch, and the third group was treated with injections of 0.5% bupivacaine hydrochloride.

In members of the lidocaine patch and bupivacaine injection groups, the investigators found significant decreases and increases in, respectively, subjective symptoms and pain thresholds. Although the effects at muscle TrPs and target areas were more pronounced in the injected patients, the lidocaine patients experienced less therapy-related discomfort. Subjective symptoms and pain thresholds did not improve in the placebo group.

TREATMENT

PHYSICAL THERAPY

Physical therapy for patients with myofascial pain focuses on correction of muscle shortening by targeted stretching, strengthening of affected muscles, and correction of aggravating postural and biomechanical factors.

Modalities can be useful in decreasing pain, allowing the patient to participate in an active exercise program.

Corrections of leg-length discrepancies with a heel lift or the use of dynamic insoles also may be helpful.

Various other techniques and procedures, including the following, have been demonstrated to be effective in some patients:

v Indomethacin phonophoresis

v Massage and exercise

v Stretching

v Electrical muscle stimulation (EMS) using interferential current (IFC), functional electrical stimulation/electrical nerve stimulation (FES/ENS), or high-frequency transcutaneous electrical nerve stimulation (TENS)

v Ultrasonography

v EMG biofeedback

OCCUPATIONAL THERAPY

Occupational therapy can be helpful in assessing and setting up ergonomically correct workstations for patients with myofascial pain. Properly set up work sites can help to decrease aggravating postural factors.

OTHER TREATMENT

Acupuncture may be helpful.
Osteopathic manipulation techniques may include integrated neuromusculoskeletal release, myofascial release, strain-counterstrain, muscle energy, and high-velocity/low-amplitude manipulation.

MEDICATION

Muscle relaxant medications and nonsteroidal anti-inflammatory

drugs (NSAIDs) can at times be a useful adjunct to active, exercise-based treatment for myofascial pain, but they are helpful only rarely on their own.

Medications such as low-dose amitriptyline may help to improve the patient's sleep cycle.

Botulinum toxin type A injected into trigger points can reduce muscular contractions through the inhibition of acetylcholine release at the neuromuscular junction and appears to have an antinociceptive effect.

Current research suggests that peripheral sensitization is blocked, which indirectly reduces central sensitization.

NONSTEROIDAL ANTI-INFLAMMATORY DRUGS

NSAIDs have analgesic, anti-inflammatory, and antipyretic activities. Their mechanism of action is not known, but they may inhibit cyclooxygenase activity and prostaglandin synthesis.

Other mechanisms may exist as well, such as the inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell-membrane functions.

IBUPROFEN (Motrin, Ibuprin, Advil)

DOC for patients with mild to moderate pain. Ibuprofen inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis.

Adult: 200-400 mg PO q4-6h while symptoms persist; not to exceed 3.2 g/d

Pediatric:

<6 months: Not established

6 months to 12 years: 4-10 mg/kg/dose PO tid/qid

>12 years: Administer as in adults

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Pregnancy category D in third trimester of pregnancy; caution in congestive heart failure, hypertension, and decreased renal and hepatic function; caution in anticoagulation abnormalities or during anticoagulant therapy

NAPROXEN (Naprosyn, Anaprox, Naprelan)

For relief of mild to moderate pain. Naproxen inhibits inflammatory reactions and pain by reducing the activity of cyclooxygenase, which results in decreased prostaglandin synthesis.

Adult: 500 mg PO followed by 250 mg q6-8h; not to exceed 1.25 g/d

Pediatric:

<2 years: Not established

>2 years: 2.5 mg/kg/dose PO; not to exceed 10 mg/kg/d

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Pregnancy category D in third trimester of pregnancy; acute renal insufficiency, interstitial nephritis, hyperkalemia, hyponatremia, and renal papillary necrosis may occur; patients with preexisting renal disease or compromised renal perfusion risk acute renal failure; leukopenia occurs rarely, is transient, and usually returns to normal during therapy; persistent leukopenia, granulocytopenia, or thrombocytopenia warrants further evaluation and may require discontinuation of drug

KETOPROFEN (Orudis, Actron, Oruvail)

For relief of mild to moderate pain and inflammation.

Small dosages initially are indicated in small and elderly patients and in those with renal or liver disease.

Doses over 75 mg do not increase the therapeutic effects. Administer high doses with caution, and closely observe the patient for a response.

Adult: 25-50 mg PO q6-8h prn; not to exceed 300 mg/d

Pediatric:

<3 months: Not established

3 months to 12 years: 0.1-1 mg/kg PO q6-8h

>12 years: Administer as in adults

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

TRICYCLIC ANTIDEPRESSANTS

Tricyclic antidepressants are a complex group of drugs that have central and peripheral anticholinergic effects, as well as sedative effects. These agents have central effects on pain transmission. They block the active re-uptake of norepinephrine and serotonin.

AMITRIPTYLINE (Elavil)

Analgesic for certain chronic and neuropathic pain.

Adult: 30-100 mg PO qhs.