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Introduction

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 there are approximately 400 muscles in the body. MP is responsible for many cases of chronic musculoskeletal pain and the diagnosis is commonly missed.

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. [1]

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. 

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. [6Patients 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.

In a study by Alonso-Blanco et al, a connection was found in women between the number of active myofascial TrPs and the intensity of the spontaneous pain and widespread mechanical hypersensitivity; nociceptive inputs from these myofascial TrPs may be linked to central sensitization.

Recent work by Shah et al using a microdialysis catheter has shown an increase in biochemicals associated with pain, including protons (a more acidic environment), inflammatory mediators, neuropeptides, cytokines, and catecholamines in the tissue around active trigger points. Uninvolved control points showed lower concentrations of these compounds, but the levels were still higher than in subjects without myofascial pain syndrome.

Physical examination

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

Many factors may contribute to the development of 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.

 Assumption of a static position for a prolonged period or conversely, performing repetitive movements, has been implicated in the condition, particularly in a cold environment.

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.

Treatment 

  1. Medicines - NSAID's, Heat/cold application, physical therapy, Manipulatiuons, shock wave, Low energy lasers etc
  2. Trigger Point Injection
  3. Botox injection
  4. Intramuscular Stimulation / Accupuncture
  5. Dextrose Prolotherapy
  6. Autologus Platelet rich plasma injection (PRP)

Dr. Kailash Kothari,

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Dr. Kailash Kothari
Director

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