Myofascial pain syndrome is a common cause of musculoskeletal pain that arises from trigger points in muscles. Trigger points are hyperirritable spots within a muscle that can generate pain locally and in other areas through referred pain patterns. Myofascial pain is estimated to affect up to 93% of people during their lifetime. This type of pain can occur in any muscle group, though it most often affects muscles of the neck, shoulders, low back, and hips.
Myofascial pain was originally thought to be caused by muscle injury or strain. However, research now shows that while muscle overload or injury can precipitate myofascial pain, it is actually caused by a sensory nervous system disorder. Myofascial trigger points irritate nerves, setting off localized pain and referred pain patterns. This has led to debate around whether myofascial pain syndrome should be classified as a true “nerve pain” disorder.
What is myofascial pain syndrome?
Myofascial pain syndrome refers to pain that originates from trigger points within muscles or surrounding fascia. The features of myofascial pain syndrome include:
- Local pain directly in a muscle containing trigger points
- Referred pain that radiates from a trigger point to other areas of the body along nerve pathways
- Pain and tenderness when trigger points are touched (palpated)
- Muscle tightness and stiffness
- Restricted range of motion
- Weakness without atrophy
Trigger points differ from tender points found in fibromyalgia. Trigger points cause pain locally as well as referred pain, while tender points only cause pain when palpated directly.
Myofascial trigger points are classified as being active or latent:
- Active trigger points – Cause constant pain symptoms both locally and through referred pain patterns. Active trigger points produce symptoms even without provocation.
- Latent trigger points – Only produce pain when stimulated. Latent trigger points may cause tightness and stiffness without generating spontaneous pain.
Active trigger points are considered the main source of symptoms in myofascial pain syndrome. Latent trigger points may develop into active ones if the underlying causes are not addressed.
What causes trigger points?
The exact mechanisms behind the development of myofascial trigger points are not fully understood. However, several factors are thought to contribute to their formation:
- Muscle overload – Excessive muscular work, fatigue, or eccentric exercises can overload muscle fibers.
- Muscle injury – Direct trauma to a muscle or injury through overstretching.
- Repetitive strain – Repeated muscle contractions through occupational or sports activities.
- Poor posture – Abnormal postures like forward head position stress muscles.
- Nutritional deficiencies – Low levels of vitamins and minerals needed for muscle function.
- Sleep disturbances – Lack of sleep interrupts muscle recovery processes.
- Psychological stress – Stress causes sustained muscle tension and spasms.
Once trigger points develop, they can self-perpetuate due to a vicious cycle called the pain-spasm-pain cycle:
- Trigger points cause pain and muscle spasms.
- Muscle spasms compress blood vessels, limiting oxygen and nutrient supply to the muscle.
- Reduced blood flow creates hypoxia, inflammation, and release of sensitizing substances like bradykinin, prostaglandins, and substance P.
- This chemical irritation and hypoxia generate more pain signals and spasms, reactivating the trigger point.
Breaking this cycle requires treatments that inactivate the trigger point and alleviate the contributing perpetuating factors.
What is the role of the nervous system in myofascial pain?
Though myofascial pain was originally conceptualized as a muscle disorder, research now implicates the peripheral and central nervous systems as major contributors to the pain.
Peripheral sensitization
Trigger points cause localized pain due to peripheral sensitization of muscle nociceptors (pain receptors):
- Chemical irritants released during the pain-spasm cycle sensitize muscle free nerve endings.
- Sensitized nociceptors fire more readily, lowering their activation threshold and amplifying pain signals.
- Nociceptors release neuropeptides like substance P that enhance sensitivity.
- Ongoing peripheral nociceptor input leads to central sensitization in the spinal cord.
Central sensitization
Trigger points also generate referred pain through central sensitization mechanisms:
- Prolonged nociceptive input from trigger points causes hyperexcitability of dorsal horn neurons in the spinal cord.
- With central sensitization, neurons fire more readily due to synaptic facilitation and disrupted inhibition.
- Afferent pain signals amplify and spread, creating expanded pain perception.
- Referred pain occurs when heightened spinal neuron responses project to uninjured areas.
Dysfunctional endplates
Another factor in myofascial pain is abnormal functioning of motor endplates. Motor endplates are the neuromuscular junctions where motor neurons activate muscles. Dysfunctional endplates exhibit hyperexcitability that causes taut muscle bands characteristic of myofascial trigger points.
Is myofascial pain a neuropathic pain?
The International Association for the Study of Pain (IASP) defines neuropathic pain as “pain caused by a lesion or disease of the somatosensory nervous system”. Based on this definition, there is debate around classifying myofascial pain syndrome as a true neuropathic disorder.
Arguments for myofascial pain as a neuropathic disorder:
- Trigger points cause peripheral and central nervous system abnormalities like nociceptor sensitization and central sensitization.
- Dysfunctional motor endplates represent a disorder of the neuromuscular junction.
- Myofascial pain shares overlapping features with other neuropathic conditions like complex regional pain syndrome.
- Treatment approaches that target neural mechanisms can be effective for myofascial pain.
Arguments against classifying myofascial pain as neuropathic:
- No structural pathology in neural tissue has been identified as the clear cause of myofascial pain.
- Muscle pathology like ischemia and contracture are still potentially important contributors.
- Myofascial trigger points are not fully equivalent to the neuropathic concept of “irritable foci”.
- Terms like “sensitization” do not necessarily equal a pathological neural lesion or disease.
There are also differing viewpoints around whether central sensitization represents a reversible neurological dysfunction vs. an actual lesion or disease process. Overall there is no consensus on whether myofascial pain definitively meets the criteria for neuropathic pain. Some experts recommend using the term “neurosensory” rather than neuropathic to describe nerve-related myofascial pain.
How is myofascial pain diagnosed?
Diagnosing myofascial pain syndrome involves:
- History of localized muscle pain and possible referred pain patterns.
- Physical exam locating tender trigger points that reproduce pain.
- Palpating taut muscle bands containing trigger points.
- Checking for reduced range of motion.
- Muscle strength testing to rule out atrophy.
- Imaging or laboratory testing to exclude other conditions.
Characteristic pain patterns can help identify which muscles contain trigger points. Common patterns include:
| Muscle | Referred Pain Pattern |
|---|---|
| Sternocleidomastoid | Head, face, ear, eye (front of head) |
| Upper trapezius | Neck, back of head, behind eye |
| Levator scapulae | Side of neck, behind ear, top of shoulder |
| Splenius capitis | Back of head, behind ear, base of skull |
| Scalene muscles | Side of neck, upper chest, shoulder, arm |
| Piriformis | Buttocks, hip, back of leg |
Differential diagnosis
Other conditions that can mimic myofascial pain include:
- Nerve compression or radiculopathy
- Arthritis
- Bone fractures
- Spinal disc pathology
- Complex regional pain syndrome
- Polymyalgia rheumatica
- Hypermobility syndromes
- Hypothyroidism
- Fibromyalgia
- Chronic fatigue syndrome
Careful history, physical exam, and testing help distinguish myofascial pain from other diagnoses.
How is myofascial pain treated?
Myofascial pain treatment aims to inactivate trigger points and prevent their reformation by addressing perpetuating factors. Common treatments include:
Trigger point inactivation
- Stretching and massage – Apply sustained pressure to trigger points to relieve muscle spasm.
- Dry needling – Insert fine needles into trigger points to cause a local twitch response that inactivates them.
- Injections – Local anesthetics or steroids injected into trigger points provide analgesia.
- Heat and cold – Heat packs and ice massage help relieve spasm and pain.
- TENS – Transcutaneous electrical nerve stimulation reduces muscle spasm and blocks pain signals.
- Ultrasound – Therapeutic ultrasound delivers deep heating to trigger points.
Perpetuating factor correction
- Ergonomic modifications – Change activities or work duties straining muscles.
- Posture correction – Improve posture through education, stretching, and strengthening.
- Muscle relaxation techniques – Apply relaxation training to reduce muscle tension.
- Stress management – Teach coping techniques like meditation to lessen stress.
- Exercise – Low-impact aerobic activity and strengthening helps normalize muscle mechanics.
- Nutritional support – Oral magnesium, vitamin D, B vitamins, and correction of deficiencies.
- Sleep hygiene – Implement proper sleep habits to ensure restorative rest.
Treatment plans are tailored to each patient and target perpetuating factors unique to their condition. Multidisciplinary rehabilitation may be needed for severe, widespread, or long-standing myofascial pain.
Conclusion
Myofascial pain syndrome involves sensory disturbances driven by peripheral and central neural mechanisms, though whether it meets criteria for a true neuropathic pain disorder remains debated. Regardless of terminology, it is clear the nervous system plays a primary role in generating myofascial trigger points and associated pain. Successful management requires normalizing neurological dysfunction through techniques that inactivate trigger points combined with correction of factors that maintain them. Further research on the neurophysiology of myofascial pain will help refine diagnostic and treatment approaches.
