Pathophysiology+of+somatic+pain+conditions

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=** Introduction **= It is a musculoskeletal pain condition characterized by **local** and **referred** pain perceived as deep and aching, and by the presence of myofascial **trigger points** in any part of the body.

The pain in MPS most commonly occurs in the head, neck, shoulders, arms, legs and lower back. However, it can occur in any muscle group.

=** What are trigger points? **= Trigger points are areas of tight, sore muscle. The pain in MPS comes from the development of trigger points in the linings of the muscles, called // myofascia //. The myofascia is a film that wraps around the muscle fibers to give them shape and support. Trigger points can develop on myofascia throughout the body.

=** Pathophysiology **=

The pathophysiology of myofascial trigger points is incompletely understood, and a number of morphologicalchanges, neurotransmitters, neurosensory features, electrophysiological features, and motor impairments havebeen implicated on its pathogenesis:

**// Morphological changes //**** : **
A significant increase in stiffness has been found within the taut band of myofascial trigger points.

**// Neurotransmitters //**** : **
Higher levels of neuropeptides (e.g., substance P or calcitonin gene-related peptide), catecholamines (e.g., norepinephrine), and proinflammatory cytokines (e.g., tumor necrosis factor alpha, interleukin 1-beta, interleukin 6, and interleukin 8) have been found in active trigger points.

**// Neurosensory features: //**
Spreading referred pain, hypersensitivity to nociceptive stimuli (hyperalgesia) and non-nociceptive stimuli (allodynia), mechanical pain sensitivity, sympathetic facilitation of mechanical sensitization, facilitation of local and referred pains, and attenuated cutaneous blood flow responses.

**// Electrophysiology: //**
Some studies have found spontaneous electrical activity, attributed to an increase in miniature endplate potentials and excessive acetylcholine release in myofascial trigger points, although future studies are needed to confirm these findings.

**// Motor impairments: //**
Myofascial trigger points can induce changes in normal muscle activation patterns and result in motor dysfunction.

** Clinical Features **
 Trigger points characteristically elicit referred pain when stimulated.  The duration of the referred pain is variable (second, hours, or days).  The referred pain is perceived as a deep, aching, and burning pain, although sometimes it may be perceived as superficial pain.  The referred pain may spread caudally or cranially.  The intensity and expanded area of referred pain are positively correlated with the degree of trigger point activity (irritability).

=** Diagnostic Criteria **= The diagnostic criteria for trigger points are under debate, but there are three minimum clinical diagnostic criteria(1–3) 1) Presence of a palpable taut band within a skeletal muscle 2) Presence of a hypersensitive spot within the taut band 3) Reproduction of a referred pain sensation with stimulation of the spot 4) Presence of a local twitch response with snapping palpation of the taut band 5) Muscle weakness or muscle tightness 6) Pain with stretching or contraction of the affected muscle

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