Exploring Advancements in Pain Mechanisms-Based Classifications

The 2018 Align Conference was packed with great presentations, but my favorite was “Pain Mechanisms: The Key to Unlocking Better Pain Solutions” by ISPI’s Steve Schmidt. This fantastic talk explored subgroups of pain mechanisms; how sensory profiling can point toward understanding an individual’s unique pain phenotype; and examined how a biopsychosocial phenotype might look.  It is said that great teachers introduce new ways of thinking, and Steve’s talk has certainly sharpened my thinking, clinical reasoning, and diagnostic understanding of pain.  Without getting too deep into the details, I wanted to share a brief summary of these topics to pass along some of my excitement and spark your interest in some really fascinating areas of pain.

The pain mechanisms-based classification work of Keith Smart (here) provided the foundation of the talk. For those unfamiliar with Smart’s work, it emphasizes the importance of recognizing and identifying a discriminatory cluster of signs and symptoms to help diagnose pain as “nociceptive”, “peripheral neuropathic”, and “central sensitization” (now referred to as nociplastic). Using a pain mechanisms-based classification to guide a diagnosis can help efficiently choose interventions and education strategies to effectively treat pain. If this is new to you, take some time to dive into the research, it is robust and well worth a deeper look (here).

With pain mechanism-based classification as the framework, here are four highlights that excited me and expanded my clinical thinking.

Take Home 1: All pain mechanisms are involved, to some degree, in all pain states; and can evolve over time.

Think pie chart percentages here. In all bouts of pain, each mechanism-based classification is represented by a certain percent. At initial evaluation you may estimate there to be 40% central sensitization, 40% peripheral neuropathic, and 20% nociceptive. Though by visit 5, the percentages may have shifted to be primarily peripheral neuropathic and nociceptive.  Thinking about classifications this way certainly shifts one’s mindset away from a linear, either/or diagnosis classification. It allows for an open and free mindset that expects pain to change and makes it ok that pain rarely fits into a single tidy category. Overall this reminded me of the evolving nature of pain and shined some light into one of the many reasons pain is so complex.

 

Take Home 2: In all cases of pain, especially in cases that do not respond as expected, it is important to consider the many subgroups that live under the top three pain mechanisms-based classifications.

  • For instance, under the nociceptive classification you will find pain that can be classified as mechanical, inflammatory, and ischemic (here).
  • There is a lot of evidence to suggest there are many different kinds of peripheral neurogenic pain. (here) (here) (here)
  • -Further considering variables that differentiate and distinguish peripheral neuropathic pain from central neuropathic pain. (here)
  • To cap off the brilliance and madness of these sub-groups, an important question was posed, “where do peripheral issues end, and central sensitization begin”. Remembering Key Point 1, this can begin to feel like a mind bender as we know peripheral nervous system changes often drive central changes and central changes often drive peripheral changes. (here)

 

Take Home 3: Sensory Profiling can point to unique and individual pain phenotypes.

Sensory profiling examines the quality of sensory information present (burning, numbness, prickling, allodynia, shooting, thermal, and light pressure). The differences between various neuropathic pain states (ie radiculopathy, painful diabetic neuropathy, and post-shingles neuralgia) (here) show how there are unique classifications for the specific pain that may inform treatment.  In another study, knee osteoarthritis sensory profiling revealed five different pain phenotypes (here). This is important as different pain phenotype likely respond better to one treatment than another. The role of pain phenotypes is a fast growing area of interest and is being studied for many neuropathic pain states. (here)  These are cool topics and will be interesting to follow in the coming years.

 

Take Home 4: Biopsychosocial Phenotypes may be an important tool for healthcare providers to learn and engage.

Think pie chart percentage once again here. Except here attempt to assign percentages for socioeconomic variables, cognitions/beliefs, emotional affective, sensorimotor, nociceptive, peripheral neuropathic, and central nociplastic. (here) This may be a more complete method to create a pain profile for optimal treatment and a more detailed pain mechanism-based classification scale. This was particularly interesting end of the presentation and has been useful to me in the clinic lately to stimulate my clinical reasoning.

Presentations like this always humble me as they highlight the complexity of pain. The more I learn, the more I appreciate how little I know.  It reminds me how much room there is to learn and grow as a PT. It excites me that better diagnosing hard-to-treat pain has the potential to help those living with it to restore function and live fuller lives.  It keeps me hungry to know more and to get better.  Has there ever been a better time to be a PT?

 

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