Myofascial Pain
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Definition[edit | edit source]
The myofascial pain syndrome is a common clinical problem of muscle pain involving sensory, motor and autonomic symptoms caused by myofascial trigger points.
A myofascial trigger point is defined as a hyperirritable spot, usually within a taut band of skeletal muscle wich is painful on compression and can give rise to characteristic referred pain, motor dysfunction and autonomic phenomena.
Classification and Clinical Presentation[edit | edit source]
Myofascial trigger points are classified into active and latent trigger points.
- An active trigger point is one with spontaneous pain or pain in response to movement that can trigger local or referred pain.
- A latent trigger point is a sensitive spot with pain or discomfort only elicited in response to compression.
The myofascial trigger points (active or latent) follow commom clinical characteristics such as:
- Pain on compression. Thit may elicit local pain and/or referred pain that is similar to a patient's usual clinical complaint or may aggravate the existing pain.
- Local twitch response. Snapping palpation (compression across the muscle fibers rapidly) may elicit a local twitch response, which is a quick contraction of the muscle fibers in or around the taut band.
- Muscle tightness. Restricted range of stretch, and increased sensitivity to stretch, of muscle fibers in a taut band may cause tightness of the involved muscle.
- Local myasthenia. The muscle with a trigger point may be weak, but usually no atrophy can be noticed.
- Patients with trigger points may have associated localized autonomic phenomena, including vasoconstriction, pilomotor response and hypersecretion.
Spontaneous electrical activity (SEA) has also been recorded in myofascial trigger point sites. The site of this electrical activity is called "active locus". SEA consists of continuous, noise-like action potentials that can range from 5 to 50 µV, with intermittent large amplitude spikes up to 600 µV. This abnormal endplate potential is caused by an excessive release of acetylcholine at the motor endplate. The magnitude of SEA is related to the pain intensity in patients with myofascial trigger points.
Etiology[edit | edit source]
Several possible mechanisms can lead to the development of trigger points, including :
- Prolonged muscle contractures: Initially the taut band formation can reflect a muscle contracture. Prolonged contractures are likely to lead to the formation of latent trigger points, which can eventually evolve into active trigger points.
- Low-level muscle contractions or Cinderella hypothesis: Myofascial trigger point pain can be caused by selective overloading of the earliest recruited and last derecruited motor units ("Henneman's size principle"). Smaller motor units are recruited before and de-recruited after larger ones; as a result, the smaller type I fibers are continuously activated during prolonged motor tasks, wich in turn it can result in metabolically overloaded motor units with a subsequent activation of autogenic destructive processes and muscle pain.
- Direct trauma
- Eccentric contractions in unconditioned or unaccustomed muscle, and maximal or submaximal concentric contractions.
References[edit | edit source]
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