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Writer's pictureDaniel Selin

Pain mechanisms

Pain, pain perception, chronic pain, neuropathic pain, nociceptive pain, nociplastic pain, central pain, burning pain, inflammation, acute pain, ischemic pain, mechanical pain, inflammatory pain, mechanism, treatment, symptoms.

At a physiotherapist's office, pain is often the primary reason for seeking treatment. However, pain can take many forms, and not all pain is treated in the same way. The underlying pain mechanisms influence the rehabilitation process, treatment prognosis, and schedule. Therefore, it is important to differentiate between pain mechanisms and select treatment based on the mechanism of pain.


In this text, we will delve deeper into pain mechanisms, their typical characteristics, symptoms, and recommended treatments. However, let's start with the definition of pain.


Definition of Pain:

The International Association for the Study of Pain (IASP) defines pain as follows:


"Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage."


Furthermore, the following statements elaborate on the definition of pain:

  • Pain is always a personal experience influenced by biological, psychological, and social factors to varying degrees.

  • Pain and nociception are separate phenomena. Pain cannot be inferred solely from activity in sensory neurons.

  • A person's culture and individual life experiences can influence pain perception.

  • A person's report of an experience as pain should be respected.

  • Although pain usually serves an adaptive role, it can have adverse effects on functioning and social and psychological well-being.

  • Verbal description is only one of many behaviors used to communicate pain; inability to communicate does not negate the possibility that a human or a nonhuman animal experiences pain.

 

Pain mechanisms

Pain mechanisms are important in the clinical assessment and planning of a patient's treatment. It is crucial to identify the underlying pain mechanism because it strongly affects the pain experience and treatment principles.


Pain mechanisms can be divided into three main groups: nociceptive pain, neuropathic pain, and nociplastic pain. It is also important to remember that there may be multiple mechanisms behind a patient's pain experience at the same time.


Psychological and social factors can also affect the pain experience and should be considered in treatment.

  • Treatment should be adapted to the dominant pain mechanism and any psychological and social factors that may limit recovery.

  • Pain mechanisms and these contributing factors can change over time.

  • The experience of pain is based on the perceived threat to the patient, which can be real or not, but the pain experience is still valid in either case. Understanding pain mechanisms can help determine how to proceed with treatment.

In the following chapter I will describe the three main groups of pain mechanisms, their characteristics and treatment principles.

 

Nociceptive pain

Nociceptive pain is pain that arises from activation of pain-sensing nerve endings due to actual or potential damage to non-nerve tissue. Nociceptive pain is typically sharp, stabbing, dull, aching, or throbbing in nature. Nonsteroidal anti-inflammatory drugs (NSAIDs) or paracetamol are usually used for nociceptive pain management, but if the pain is severe, opioids may also be considered.

Examples of nociceptive pain include:

  • Osteoarthritis

  • Pain after sprains

  • Acute inflammatory reaction

  • Strain

  • Bruise

  • Tear

  • Contusion

Nociceptive pain typically responds well to manual therapy, and at least partial pain relief is often immediate. This is known as an intra-treatment change, which is an important factor in prognosticating and developing a treatment plan. If the pain relief obtained from the treatment persists until the next appointment, the prognosis for recovery is excellent, and the chosen therapy should be continued as part of the rehabilitation process.

Nociceptive pain itself can also be further categorized as either mechanical, inflammatory, or ischemic in origin. Each type of pain has its own characteristics and treatment principles.

Mechanical pain

Mechanical pain refers to pain that is caused by mechanical stress or damage to

the body's tissues or structures, such as joints or muscles. This type of pain is often

localized, well-defined, and aggravated by specific movements or positions. It

usually subsides when the aggravating movement is avoided or the underlying

issue is treated.


Mechanical pain is typically short-lived and has a good prognosis.

Painkillers are usually not necessary as the discomfort is often mild. Manual

therapy such as joint mobilization, manipulation, soft tissue therapy, acupuncture,

and stretching exercises are effective in managing mechanical pain. Common

examples of mechanical pain include facet joint dysfunction, rib dysfunction, and

other joint or muscle injuries.


Inflammatory pain

Inflammatory pain is often experienced as a localized throbbing or pulsating pain,

and is often accompanied by a rise in temperature and swelling in the affected

area. Resting pain is also often associated with this type of pain, which is why

movement or elevating the area can help relieve it. There is often a clear cause for

the pain, which explains the underlying condition.


If the pain is severe, anti-inflammatory pain medication usually provides relief. The

prognosis is good and spontaneous recovery is typical. Pain can be treated with

light mobilization and movement. Typical inflammatory pain conditions include

post-strain or sprain pain, as well as tendon and joint pain.


Ischemic pain

Ischemic pain is often experienced as exhausting, numb, and may be

accompanied by a feeling of tension or the sensation of being about to snap.

Ischemic pain is worsened by monotonous active postures such as prolonged

standing, sitting, or static work. Moving, physical activity, muscle activation, soft

tissue treatment, and other activities that increase blood flow to the area can help

alleviate ischemic pain. The pain is often related to daily activities, and pain-

promoting activities have often been continued for a long time before the onset of

symptoms.


Pain medication is rarely necessary, and the pain is often not worrisome. The

prognosis is theoretically good, but recovery often requires a change in one's own

behavior. The background often involves hypermobility, muscle weakness, and

ergonomic challenges.

 

Neuropathic pain

Neuropathic pain is caused by damage or disease in the nervous system. It is characterized by a burning, stabbing or shooting pain, and often includes changes in sensation or numbness that follow the neuroanatomical distribution of the damaged nerve. Certain positions or movements may worsen neuropathic pain, but it can also be provoked without any external cause.


Support, taping, light manual therapies, or the use of assistive devices can help alleviate the pain. However, pain is usually more unpredictable than in nociceptive pain. In the treatment of neuropathic pain, stronger medications are typically used than in the treatment of nociceptive pain. Typical medications include amitriptyline, gabapentin, opioids, pregabalin, duloxetine, or venlafaxine.


Examples of neuropathic pain:

  • Diabetic neuropathy

  • Cervical radiculopathy

  • Pain related to myelopathy

  • Pain related to multiple sclerosis (MS)

  • Thoracic outlet syndrome (TOS)

  • Trigeminal neuralgia

Manual therapy is often effective in the treatment of neuropathic pain, but the techniques used are different from those used in the treatment of nociceptive pain. In neuropathic pain, the aim is to reduce pressure on the nerve tissue or improve its sliding properties. Treatment is often considerably lighter than the treatment used in nociceptive pain.


The prognosis varies and is somewhat unpredictable, but symptoms are often more long-lasting than in nociceptive pain.

 

Nosiplastic pain

Nosiplastic pain, also known as central pain, is pain that is felt even though there is no clear evidence of real or impending tissue damage or disease or damage to the somatosensory system. In chronic pain, there is often nosiplastic pain mechanisms involved.


Nosiplastic pain is characterized by sharp or dull pain that is felt over a wide area and often accompanied by tingling, numbness, or a pins-and-needles sensation. It is much more vague than nociceptive or neuropathic pain and there may not be any provoking or relieving positions or movements. Often it feels like the pain is doing whatever it wants and cannot be controlled in any way.


The medications used to treat nosiplastic pain are generally the same as those used for neuropathic pain, such as amitriptyline, gabapentin, pregabalin, duloxetine, or venlafaxine. Opioids are also used, but their long-term effects appear to be limited.


Examples of nosiplastic pain include:

  • Fibromyalgia

  • Migraine

  • Irritable bowel syndrome (IBS)

  • Chronic headache

  • Chronic neck pain

  • Complex regional pain syndrome (CRPS)

  • Temporomandibular joint disorders (TMD)

  • Chronic back pain

Manual therapy is not typically very effective for nosiplastic pain, and other approaches are usually focused on instead. Manual therapy that is too forceful or done too close to the painful area can actually increase pain, which often worsens over time. However, manual therapy can be used as part of a comprehensive treatment plan as long as gentle techniques are used and areas that are not particularly painful are targeted.


The goal is often to modulate descending pain pathways, promote muscle relaxation, reduce cortisol secretion, or decrease inflammation. The aim of treatment is more focused on pain relief than on biomechanical changes.


However, it is important to approach the problem in a multidisciplinary manner and increase the pain sufferer's understanding of pain. Often, a pain team is created, consisting of a physiotherapist, a specialist in physical medicine, pain and rehabilitation, and a pain psychologist. Biopsychosocial factors appear to be a contributing factor in the prolongation of pain, so addressing these factors can also help alleviate pain.

 

Summary

In summary, it's important to distinguish between different types of pain and tailor treatment accordingly. The mechanisms of pain describe how pain is perceived and by utilizing this knowledge, an accurate and effective treatment plan can be created for pain relief.





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