Myofascial Pain (MPS) is a noninflammatory disorder of musculoskeletal origin, associated with pain and muscle stiffness, characterized by the presence of hyperirritable palpable nodules in the skeletal muscle fibers, which are termed MTrPs. These trigger points are the cardinal feature of MPS and hence differentiate it from other painful MPSs such as inflammatory myositis and fibromyalgia. (Saxena et al, 2015).
- MPS is the most common cause of continuous regional pain.
- MPS has sensory, motor, and autonomic features, and is characterized by the presence of local and referred pain, limited range of motion, in addition to muscle weakness.
- MPS predisposing factors fall under one of 4 categories (psychological, ergonomic, structural, and systemic). Some examples are emotional stress, nutritional deficiencies, scoliosis, poor posture, parafunctional habits, muscular tension, a history of a whiplash injury, and poor sleep quality.
- Comorbid conditions that may accompany and/or trigger MPS include TTHA and TMDs.
Myofascial Trigger Points (MTrP)
MTrP is a hyperirritable spot in a taut band of a skeletal muscle, which is painful on compression, stretch, overload, or contraction of the muscle and usually has a distinct referred pain pattern.
Pathophysiology of MTrPs
The integrated hypothesis is the most accepted theory for explaining the pathophysiology of MTrP. It proposes that MTrPs occur as a result of an abnormal acetylcholine release at the level of a dysfunctional motor endplate resulting in sustained contractile activity of skeletal muscle fibers. The continued contractions, in turn, lead to the depletion of ATP, the release of pro-inflammatory substances, ischemia, and the localized hypoxic energy crisis which is associated with sensory and autonomic reflex arcs that are maintained by complex sensitization mechanisms.
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Classification of MTrPs
Active TrP produces 2 types of pain:
- Spontaneous pain
- Elicited pain: compression of an active TrP produces local pain or referred pain to a predictable reference zone, accompanied by motor and autonomic symptoms. The elicited pain reproduces the patient’s familiar pain complaint.
Latent TrP: may have all the other clinical characteristics of an active TrP with the main difference being painful only if palpated or compressed.
Mechanical stimulation of MTrPs can elicit different responses
- A jump sign refers to the movement or jumping of the patient when a TrP is pressed, and this indicates a high sensitivity of the palpated spot.
- A local twitch response (LTR) can be elicited by needle insertion or snapping palpation of TrP. The LTR is a contraction reflex that is unique to TrPs.
- Pain referral: is simply a mislocalization of pain; continuous pressure on a TrP results in pain sensation in a region that is located remotely from it. The most famous theory that explains this phenomenon is the conversion-projection theory.
Features of MPS
- Regional pain – It can be persistent, paroxysmal, or burning. (Associated with sensory changes and numbness. Aggravated by muscle function and cold.)
- Muscle stiffness/ weakness
- Restricted range of motion
- Dysautonomia: lacrimation, diaphoresis, flushing, dermatographia, temperature changes, and pilomotor activity.
- Psychological symptoms: anxiety and depression
Diagnosis of MPS
MPS is diagnosed by muscle palpation and identification of the presence of myofascial trigger points and associated familiar pain. The manual palpation force can be established and performed efficiently by using a pressure algometry (usually between 2-4 kg/cm²).
When a trigger point in a taut band is suspected and located, the pressure of palpation over the TrP should be maintained for 10-20 seconds to determine if a pattern of pain referral is elicited.
When the source of pain is difficult to identify, a diagnostic anesthetic injection delivered to the trigger point can be very helpful to confirm the diagnosis. (Okeson et al, 2013).
Differential diagnosis of MPS
- Chronic fatigue syndrome
- Polymyalgia rheumatica
The main goal of MPS management is to decrease or eliminate pain symptoms, increase mouth opening to normal and improve the quality of life.
- Manual therapy (includes spray and stretch which entails the application of a cooling spray containing fluoromethane or ethyl chloride while simultaneously passively stretching the involved muscle, myofascial release, and deep massage). Stretching and physical therapy are the mainstays of MPS management.
- Ultrasound stimulation
- Behavioral treatment
- Thermal treatment
- Occlusal splint
- Sleep hygiene
- Dry needling
- Muscle relaxants
- Trigger point injection with lidocaine
- Trigger point injection with botulinum toxin A
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