In the previous blogs, we have seen that pain is complex, and multiple systems work together to manage healing and pain responses. In this blog, we will briefly look at historical and contemporary ideas of pain theory. We will also look at how these ideas can be leveraged for treatment.
What does historical thought say?
Thoughts on pain have developed since antiquity.
- Plato foreshadowed the intensity theory when he labeled pain as an emotion that occurs when a stimulus is intense and lasting.
- Galen furthered thought by hypothesizing that perception requires an organ to receive stimulus, a connection from the organ to the brain, and a processing center to convert the sensation to a perception. While Galen recognized the importance of the brain, the specific structures and mechanisms were still a mystery.
- Descartes capitalized on available pain science in the 1600s to propose the Cartesian theory. This theory postulated that pain is the result of physical or psychological injury. He also established a connection between a stimulus, the nerves, and the brain. He compared sensation to a string attached to a bell. An individual can tug on a string to transmit force to the bell, and the bell will ring. For example, clothing brushes against the skin and activates a nerve. The nerve conducts the signal to the brain, and the stimulus is felt as touch.
Further, the following developments laid the groundwork for theories that still influence present day thought.
- Bell proposed the specificity theory in 1811. He argued that distinct sensory modalities exist such as touch, pressure, and heat which are carried by dedicated nerves. Eventually, pain was also recognized as a distinct sensation. He also believed that each modality had a unique sensory receptor.
- In contrast to Bell, Erb proposed the intensity theory in 1874. He argued against pain as a distinct sense. He believed that pain was caused when normal sensory stimulus reached a high intensity.
- In 1965 Melzack and Wall combined multiple theories with the proposal of gait control theory. They argued that distinct pain signals must be relayed through the spinal cord to reach the brain, and the spinal cord can “gate” the signals. The intensity of the signal must be strong enough to open the gate. They also argued that disease processes and emotional state can allow the gate to open more easily.
Where did it lead?
Currently, the biomedical model of injury and disease is commonly used to address painful conditions. This model is influenced by historical theories of pain as far back as the Cartesian theory, but it has not fully embraced contemporary theories on pain. It subscribes to a cause-and-effect relationship of tissue injury and pain, and it is focused on the effects of specific injury and specific pathology.
As it relates to pain, this model makes the following basic assumptions:
- A proportional relationship exists between the amount of pain experienced and tissue damage.
- A linear relationship exists between the magnitude of tissue damage and the amount of physical limitation that results.
- Treating the damaged tissue or pathology will resolve the pain and limitation.
This approach has significant limitations:
- It struggles to explain pain that persists past normal healing phases.
- It struggles to explain magnitudes of pain that differ from the extent of an injury.
- It fails to explain why similar injuries may respond differently to the same treatments.
- It also assumes that an injury or pathology still exists and that we can correctly identify an offending tissue.
The limitations with this model hint that pain is complex and multifactorial. Luckily, contemporary models of pain theory have expanded their scope from specific tissue injury. Most contemporary models recognize pain as its own disease process, acknowledge the whole person, and examine the influences of a social ecosystem.
Contemporary thought places greater emphasis on processing, social influences, and emotional influences.
- In 1968 Melzack and Casey described pain as multidimensional experience that is influenced by sensory, emotional, and cognitive components.
- In 1998 Gifford molded these domains into the mature organism model. This model places pain in the context of a stress response. It accounts for environmental factors, sensory inputs, processing, and output responses.
- Melzack further elaborated on processing with neuromatrix theory in which he recognizes that diverse networks of neurons within the brain are recruited with each sensory input to provide context to what we feel.
- The biopsychosocial model continued to build on pain theory by recognizing the influence that relationships, family structure, social background, and economic standing can have on an individual’s pain.
Pain as a disease and pain mechanisms
Contemporary theories of pain position pain as its own complex disease process. To better understand and treat pain as a disease, we can examine pain mechanisms. Pain mechanisms are the nuts and bolts that generate, magnify, and maintain painful conditions; and they can be used to contextualize symptoms and guide treatment. Three broad categories of pain mechanisms are described.
Nociceptive pain is what we typically think of during the normal course of injury healing. An area is irritated with the initial injury. It progresses through phases of inflammation, tissue mending, and refinement. Most of the perceived pain is directly related to nerve signaling from the irritated area, and symptoms are relatively limited to the area of injury.
To continue Julie’s story from the last blog, she felt nociceptive pain when she initially strained her calf. This pain presentation generally follows a pattern. Her calf was irritated when it was stressed during runs. To a lesser extent, it was bothered with walking. She felt relief when she sat or slept when she did not stress her calf. Her symptoms were local to the site of the injury and the muscle’s attachment, and she felt either a dull ache or sharpness depending on her activity level. Her symptoms rarely spread, and she did not have strange sensations like burning, tingling, or numbness. With this presentation, she would normally recover with a short period of rest (1-2 days), direct exercise to address the injured area, and a controlled ramp up to her prior mileage. Though, in her case, she continued to push forward with her training without respecting her symptoms.
This is what nociceptive presentations look like:
- Pain is provoked and relieved with a consistent set of movements and behaves with an on/off pattern
- Pain is in a localized area
- Pain is proportionate to the intensity of irritating activities
- Pain is described as achy, sharp, or dull rather than burning, shooting, or electric
- Pain does not coincide with numbness and tingling
Neuropathic pain is a presentation that we typically associate with nerve injury and irritation. Nerves are long structures that send signals throughout the body, and they are electric in nature. When a nerve is irritated, it can cause symptoms along its entire path, and the symptoms can mimic electric sensations like an electric shock, static, tingling, and numbness.
Julie is fortunate that she does not have a neuropathic pain presentation. She is struggling with local calf pain that she directly associates with a running related injury. A neuropathic presentation would be a consideration if she had prior history of nerve involvement in her lower back or lower leg. Similarly, she primarily complains of sharp pains or aches. She does not have the electric sensations that are typically associated with nerve irritation. If she had neuropathic pain, we would expect it to respond to a combination of gentle nerve movement and movement curation to reduce the stress on irritated neural tissue.
This is what a neuropathic presentation looks like:
- Nerve injury or pathology can be identified in a person’s history
- Pain radiates in the path of an affected nerve
- Pain is primarily present with movements that stress the affected neural tissue
Nociplastic pain is a complex presentation of symptoms that reflects increased involvement from areas that help relay and process nerve signals. In this presentation, these processing centers act to amplify nerve signals which magnify and perpetuate symptoms. Further, the increased activity in these areas opens the door for other inputs to affect pain presentations such as emotion, memory, and seemingly unrelated sensory signals.
Julie is on the cusp of developing a nociplastic pain presentation. Her symptoms are becoming less predictable. Previously, her symptoms were only irritated with running and walking. Now, her symptoms are present constantly. She even feels symptoms when she is off her feet, and she is noticing increased sensitivity in her heel and calf to light touch. Her symptoms have spread to her foot and knee. She is also noticing other areas of pain in her lumbar spine and opposite foot. Further, she is feeling exhausted from her running training, and she feels stressed and unsure about her foot pain that is worsening.
At this point, a standard treatment program would be marginally helpful, but she would benefit from more specific management. She needs strategies to manage an overworked stress system. She needs another pair of eyes to identify and explain why her symptoms are progressing and how each piece is interrelated. Finally, she needs supervised and gradual exposure to exercise to fully return to running without exacerbating her symptoms.
This is what nociplastic presentations look like:
- Pain seems disproportionate to the nature of the injury or pathology
- An unpredictable pattern of pain is present, and it is aggravated by diverse activities that do not form a consistent pattern
- Strong individual and social influences are present such as negative emotions, feelings of helplessness, fears associated with pain, and altered social dynamics
- Widespread areas are sensitive and reactive to light pressure and touch.
Why does this matter?
As you can see, the pathways of pain are complex in nature. Correctly evaluating pain mechanisms can be the difference in a successful and unsuccessful treatment. Awareness of pain mechanisms can:
- mitigate common points of failure in treatment programs
- explain seemingly odd symptom presentations
- allow for appropriate adjustments in treatment intensity
- hone treatment selection
At STAT, our physical therapists understand how to manage painful conditions so that you can return to the activities that you love. In addition to assessing nagging injuries, movement limitations, and overall fitness, we use contemporary pain theory to maximize the pace of your recovery.
We use hands on approaches such as dry needling, cupping, and joint mobilization to address local roots of pain. We use neural mobilization and curated movements to address neural elements of pain. We use graded exploration of movement patterns, cues for mindfulness, and stress management techniques to address changes in relay and processing centers that magnify pain. Further, we also offer functional medicine, health coaching, and nutrition counseling to comprehensively address all the complexities that pain presents. If one of these presentations seems too familiar to you, book a visit or FREE consultation with one of our amazing providers HERE!