An important dichotomy in the current literature is whether the myofascial trigger point is a cause or effect of chronic myofascial pain. The Integrated Hypothesis is the current prevailing theory characterizing the enigmatic pathophysiology of chronic myofascial pain and posits that the myofascial trigger point (MTrP) is the primary pathologic focus (cause) mediating the clinical manifestations of chronic myofascial pain. According to this hypothesis, myofascial pain is triggered by an injury of the muscle, either acute or chronic, leading to local contracture as a result of spontaneous release of acetylcholine at a dysfunctional motor endplate.

Emerging research suggests, however, that neurogenic mechanisms may play a foundational role. Apropos, the Neurogenic Hypothesis proposes that the dynamic clinical manifestations of chronic myofascial pain are initiated, amplified and facilitated by central sensitization, in the absence of overload injury to the muscle. Central sensitization is caused by the persistent bombardment of nociceptive impulses from a primary pathologic source, either somatic (e.g., discopathy, degenerative joint, MTrPs, etc.) or visceral.

An important sequela to central sensitization is neurogenic inflammation - a neuro-inflammatory response caused by retrograde (anti-dromic) release of vasoactive and pro-inflammatory neuropeptides, predominantly Substance P, into peripheral tissues (either somatic and/or visceral) via sensory nerves.

The Neurogenic Hypothesis suggests that the MTrP is a secondary manifestation (effect) of neurogenic inflammatory mechanisms expressed peripherally within skeletal muscle. Through interneuronal pathways, spinal sensitization may also influence sympathetic activity via pre-ganglionic sympathetic fibers located within the intermediate horn, as well as enhancing motorunit pool excitability within the neurosegmentally linked ventral horn. Once this process is initiated, activation of muscle spindles may facilitate persistent muscle fiber contractures commonly observed with chronic myofascial pain.

The presenters:

Jay P. Shah, MD, Physiatrist, National Institutes of Health

Jay P. Shah is a physiatrist and clinical investigator in the Rehabilitation Medicine Department at the National Institutes of Health in Bethesda, Maryland USA. His interests include the pathophysiology of myofascial pain and the integration of physical medicine techniques with promising complementary approaches in the management of neuro-musculoskeletal pain and dysfunction.

John Z Srbely DC PhD, Associate Professor, University of Guelph

John Srbely is a full-time Associate Professor in the Department of Human Health and Nutritional Science, University of Guelph (Guelph, Ontario, Canada). He previously held a Canadian Chiropractic Research Foundation (CCRF) Research Chair in Spine Mechanics and Neurophysiology (2008-2013).

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