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Pain classifications part 2: nociception

By Elliott Perkins


This is part 2 of a multipart series on classifying pain. Read part 1 here.


A patient presents to the clinic with low back pain. The pain remains localized to the low back, with no radiating pain into the legs. The pain is reported as intermittent, absent when lying down and when walking, aggravated with prolonged sitting, bending forward and twisting. Lumbar extension is reported as relieving. The pain is present at night, but only with position changes, and is absent when in a comfortable position. No red flags are present, neurological exam is within normal limits, and their health history is otherwise unremarkable.


Does this sound familiar? This is a common presentation for many patients who come into my office, and is an example of the ‘Nociceptive” classification of pain. Through pattern recognition in patient symptoms and coping strategies, we can determine the dominant pain phenotype, which can better help us identify our patients needs, and guide our management. This is especially important when we are dealing with patients suffering from persistent pain. The nociceptive classification is by far the most common we come across in clinic , and typically has the most positive outcomes to conservative treatment (Smart et al., 2012).


As we have discussed earlier, pain is a complicated animal. Pain is an experience between a person and their environment (Stillwell et al., 2019). As mentioned in part one; emotions, stress and past experiences can play a role in the pain experience and must all be individually addressed. One of these stimuli is called nociception, and it is happening all the time.


What is nociception?


Imagine there is an army gathering for battle. Their scouting party is attacked by a rival band of soldiers, but they manage to send a messenger back to the base. After arriving at the base and informing his commanders of the threat, the decision is made to muster the army to respond. If the ‘commander’ is the brain, the messenger is ‘nociception’.


Remember, pain is the perception, not the input. The input is nociception. Nociception is happening all the time but does not always cause a pain response (Smart et al., 2012).


Nociceptive pain occurs from actual or the potential threat of damage to non-neural tissue (neuropathic pain is a different beast that we will get into later). Nociceptive pain has a high threshold, meaning it requires a certain amount of stimulation of nociceptors (“free nerve endings”, C and A-delta fibres). Therefore a light touch doesn’t typically cause pain, but deep pressure or a sharp poke may. Activation of these nociceptors of a sufficient magnitude may cause a response – aka pain. Pain is not proportional to the amount of tissue ‘damage’, as we can often experience pain with no actual tissue damage present! Note that this is not limited to acute pain, as patients can experience chronic nociceptive pain.


In the case of actual tissue damage, nociceptive inputs can also cause an inflammatory reaction. An acute inflammatory response typically lasts anywhere from 0-3 weeks. Remember, Inflammation is good! It aids in the healing of injuries, and we need it to survive. Only when inflammation runs rampant and gets excessive (e.g. inflammatory conditions like rheumatoid arthritis) do we want to try to actively reduce the inflammatory process.


Why does inflammation hurt?


Inflammation plays a big role in nociceptive pain. The presence of inflammation decreases the threshold of the nearby peripheral nociceptors (those “free nerve endings” mentioned earlier), causing them to send a signal to the brain with much less stimulation. This explains why when you roll your ankle and it swells up, simple movements such as walking can be painful when they would typically be perfectly benign and natural.


What do we do when there is an acute inflammatory reaction?


We baby it to let it heal. The body is just doing its thing, repairing damage and restoring the natural order of things. Its short lived, naturally improves, and as it improves, we can gradually return back to normal activities, no harm no foul.


I say again, Nociception/inflammation =/= pain. Prof. Moseley says, “pain is now considered a conscious experience that can be, and often is associated with nociception, but is always modulated by a myriad of other neurobiological, environmental and cognitive factors” (Moseley, 2015). Simply put, that old diagram of “foot in fire = pain in brain” does not accurately encompass our modern understanding of the complexities of pain. Pain is an experience that nociception can influence.



How can we identify a patient with a nociceptive pain classification?


Looking back to the example case of low back pain at the start of the article, we can see a clear, proportionate, mechanical nature to aggravating and relieving factors. Certain things hurt, other things don’t. The pain typically remains well localized and is usually intermittent. Often described as ‘sharp’ (but not always, pain is a personal thing). It can be provoked with movement/provocation (be it orthopaedic provocative testing, or certain physical tasks). If an inflammatory reaction is ongoing, the pain can be constant, however it is typically a dull ache at rest. Typically, we are looking at a patient that has no dysesthesias or nerve related sensory changes, and no disturbed sleep. If the patient has pain at night, it is typically present with movement or certain sleeping postures. Sometimes the patient will present with an antalgic posture or movement patterns. This is the patient’s way of naturally adapting to the mechanical nature of the pain, adopting a more relieving posture. Sometimes referred pain is present, but it is typically transient/modifiable, and a sharp shooting pain that remains localized to a certain area rather than diffuse and spreading.


Patients with nociceptive pain typically respond well to traditional conservative therapies like exercise and manual therapy. Certain individuals are more ‘pain adaptive’ and respond better to these interventions than others, and they also respond better to self-management strategies as well.


(Check out this podcast with Dr. Chad Cook all about manual therapy and pain adaptive patients https://www.clinicaledge.co/podcast/physio-edge-podcast/093)


How do we best manage a patient with nociceptive pain?


1. Educate! It is very important to make sure the patient knows exactly what is going on. They need to know that what they are experiencing is common, will get better, and isn’t necessarily caused by actual tissue damage. Describing the pain as a “tissue sensitivity” is useful, because there is often no actual tissue damage, and this narrative helps to promote a proper understanding of hurt vs harm.


2. Educate the patient on the nature of inflammatory pain as described above. The PEACE & LOVE (the graphic is below) mnemonic is a useful self-management strategy. In cases of inflammation, mid-range movements can help to decrease pain. Whether you are a coach, Chiropractor, Physiotherapist or Trainer, remember to stay within your scope! Sometimes anti-inflammatory medications are useful and referral to the patient's GP is warranted.



3. Teach the patient how to modify their symptoms. My preferred way to do this is to identify and have the patient adopt a preferred loading strategy. Can we change how the patient performs tasks so that we don’t aggravate their symptoms? Does movement in any certain direction help to reduce their symptoms?


4. Promote active participation in their recovery.

Step 1: if something aggravates your pain, avoid doing that thing for a little while, so you can desensitize the sensitive structures. Stop “picking the scab” if you will.

Step 2: find what movements feel good and do those movements A LOT. No pain with walking? Get some mileage under your belt! Do repeated prone extensions (a la McKenzie sloppy pushups) help to centralize your pain and reduce symptoms? Do them regularly throughout the day.


Step 3. Once symptoms have reduced to a tolerable level, start re-introducing those movements that were previously painful in a gradual, controlled manner. No movement in inherently bad, but we don’t want to do too much too quick.


5. General exercise – exercise will make you less sensitive to loading the tissue. This can take time, so stick with it! The secondary benefits of exercise cannot be understated. Not only is it powerfully analgesic, we have increases in cardiac output, muscle mass, bone density, and increased blood flow to areas undergoing tissue healing. It also teaches patients that movement is safe, not painful, and they don’t have to fear activity. Win-win-win-win!


6. Manual therapy: use as an adjunct to active therapy. Manual therapy and passive modalities do have their use in pain conditions like this, for temporary relief. It is important for your patients to understand that passive therapies are not fixing anything, and that they are able to control their own pain without needing hands on therapy. Build your patients up! Teach them to be independent, and self-efficacious!

What about radiculopathies?


Good question, Elliott. Radiculopathies can potentially be classified as neuropathic pain, since neural tissue is involved. However, radiculopathies can and frequently are nociceptive dominant (the question of radiculopathy vs. radicular pain vs. somatic referred pain is one we will have to get into later. Much later.) We see this with how it responds to mechanical therapies to the spine. Directional preferences (e.g. extension) can centralize (reduce leg pain) and modify the symptoms, and manual therapy to the spine can have a reduction in symptoms as well. It is imperative to assess your patient as an individual and treat them as an individual based on their own pain experience/needs, rather than just treating the condition.


I am personally a fan of using “directional preference” or “preferred loading strategies” for managing nociceptive pain, as it teaches the patient how to modify their symptoms on their own through exercise. I’ll write another article sometime about how I use directional preferences as a tool to guide my rehab, but it’ll be a little while yet. I’m just getting started here.


I will once again shamelessly promote the course “Chronic Pain Diagnosis and Mangement for Healthcare Providers” instructed by our own podcast guest Dr. Demetry Assimakopulous. I’m just scraping the tip of the iceberg here. Check out our interview with him here.



References:


Hollmann, L., et al. “Does Muscle Guarding Play a Role in Range of Motion Loss in Patients with Frozen Shoulder?” Musculoskeletal Science and Practice, vol. 37, Oct. 2018, pp. 64–68. DOI.org (Crossref), doi:10.1016/j.msksp.2018.07.001.


Smart KM, Blake C, Staines A, Thacker M, et al. “Mechanisms-Based Classifications of Musculoskeletal Pain: Part 1 of 3: Symptoms and Signs of Central Sensitisation in Patients With Low Back (± Leg) Pain.” Manual Therapy, Aug. 2012, doi:10.1016/j.math.2012.03.013.


---. “Mechanisms-Based Classifications of Musculoskeletal Pain: Part 2 of 3: Symptoms and Signs of Peripheral Neuropathic Pain in Patients With Low Back (± Leg) Pain.” Manual Therapy, Aug. 2012, doi:10.1016/j.math.2012.03.003.


---. “Mechanisms-Based Classifications of Musculoskeletal Pain: Part 3 of 3: Symptoms and Signs of Nociceptive Pain in Patients With Low Back (± Leg) Pain.” Manual Therapy, Aug. 2012, doi:10.1016/j.math.2012.03.002.


Smart KM, Blake C, Staines A, and Doody C. “The Discriminative Validity of ‘Nociceptive,’ ‘Peripheral Neuropathic,’ and ‘Central Sensitization’ as Mechanisms-Based Classifications of Musculoskeletal Pain.” The Clinical Journal of Pain, Oct. 2011, doi:10.1097/AJP.0b013e318215f16a.


Stilwell P, Harman K. An enactive approach to pain: beyond the biopsychosocial model. Phenomenol Cogn Sci. 2019;8(4):637-665.


Kolski, Melissa C., and Annie O’Connor. A World of Hurt: A Guide to Classifying Pain. Thomas Land Publishers Incorporated, 2015.


Lin I, Wiles L, Waller R, et al . What does best practice care for musculoskeletal pain look like? Eleven consistent recommendations from high-quality clinical practice guidelines: systematic review.British Journal of Sports Medicine 2020;54:79-86.

McKenzie, Robin, and Stephen May. The Lumbar Spine, Volume One: Mechanical Diagnosis and Therapy. Spinal Publications, 2003.


Moseley, Lorimer & Vlaeyen, Johannes. (2015). Beyond nociception: the imprecision hypothesis chronic pain. Pain. 156. 10.1016/j.pain.0000000000000014.

Moseley, Lorimer G., and Arnoud Arntz. “The Context of a Noxious Stimulus Affects the Pain It Evokes:” Pain, vol. 133, no. 1, Dec. 2007, pp. 64–71. DOI.org (Crossref), doi:10.1016/j.pain.2007.03.002.


Walton, David M., and James M. Elliott. “A New Clinical Model for Facilitating the Development of Pattern Recognition Skills in Clinical Pain Assessment.” Musculoskeletal Science & Practice, vol. 36, Aug. 2018, pp. 17–24. www.mskscienceandpractice.com, doi:10.1016/j.msksp.2018.03.006.