Putting Pain in a New Perspective, Or

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Putting Pain in a New Perspective, Or

• Mary Christenson, PT, PhD
• DPT 781 O

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What Makes Pain Matter?

• Traditional Model
• Papercut stimulates free nerve endings of
  mechanical nociceptors
• Travels via A delta and C fibers to the dorsal
  horn of the spinal cord
• Synapse on second neuron in substantia gelatinosa
  / T cell, crosses midline and joins the
  anterolateral spinothalamic system
• Travels to ventral posterior lateral nucleus of
  thalamus where synapses on third neuron
• Information carried to area of the primary
  somatosensory cortex which interprets papercut -
  pain

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Personal Stories Need for a New Model?

• Phantom Limb Pain
• CRPS
• Traumatic injuries where a greater threat is
  perceived
• Life more important than pain
• Step on a Tack
• Basic
• Up a notch

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Pain versus Tissue Injury

• Pain does not provide a measure of the state of
  the tissues. 1
• people with bad OA and no pain?
• people with bad disc protrusion and no pain?
• Etc.

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Questions

• Have you ever had no pain with damage to your
  body?
• Have you ever experienced pain when no damage has
  occurred to your body?

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The Threat

• Get pain when brain perceives there is a
  potential for danger to tissues and action is
  needed
• The brain is managing countless messages in very
  short time intervals determines priorities

Brain Orchestra per Butler and Moseley2
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Rethinking Sensors

• Sensors receptors reporters2 keeping track
  of the bodys business
• Located in walls and at the free nerve endings of
  neurons
• Stimulation can open receptors, ions exchanged,
  action potential
• Rapid turnover of sensors? Importance?
• Can increase/decrease in number Result?

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Spinal Cord Involvement

• Messages can come from the brain to shut down
  neurotransmission of signals from 2nd order
  neurons (danger messengers1)
• Powerful chemicals (stories) reverse flow of ions
  and therefore can stop signals

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Rethinking the Brains Involvement

• Many centers in the brain involved in pain to
  interpret and respond
• Pre-motor/motor cortex
• Cingulate cortex
• Pre-frontal
• Amygdala
• Sensory cortex
• Hypothalamus/ thalamus

• Cerebellum
• Hippocampus2

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Peripheral Sensitization

• Increased responsiveness to stimuli after initial
  injury
• Potential mechanisms
• Lower threshold to stimulus
• Increase in neuron activity
• Increase in area of receptor fields
• Increase in response to the same stimulus

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Central Sensitization

• Neurons in dorsal horn
• High-threshold respond to noxious stim
• Low-threshold respond to innocuous stim
• Wide-dynamic-range (WDR) respond to both
• Tissue injury increased sensitivity of
  high-threshold and WDR neurons
• Expansion of receptive fields in central neurons
  common
• As pain persists, neurons in brain that induce
  pain become sensitized

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Sensitization

• Continued input from sensitized nociceptors can
  maintain sensitization of dorsal horn neurons
• Need to reduce peripheral input?
• Sensitization of dorsal horn neurons can also be
  maintained in absence of peripheral input
• Need to reduce central sensitization?

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Multiple Sites within the Brain Decision-Making
Power

• Brain has billions of neurons each neuron can
  connect with up to 5000 other neurons

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At first glance Is the yellow panel in front or
back?
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The Neuromatrix Model

• Pain is Complex
• The Neuromatrix Theory2
• Neuromatrix distributed throughout brain
• Wide network of neurons that generate patterns
• Processes information flowing through it
• Produces a pattern felt as whole body
• Pain is an event that takes up part of this space
• Event space neurosignature

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The Threat Danger

• Body Perceives a Threat
• Many systems engage
• Endocrine/hormones down and up regulate
• Motor Mobilizes
• ANS
• SNS increase HR, metabolism, awareness
• PNS will act in healing processes
• Immune fight invasion, heal, sensitize
• Pain motivator get help, prompt to move
• Pain may be the conscious response to threat

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It is the perception of the threat that
determines the output, not the tissue damage
itself or threat to the tissues1Neuromatrix
TheoryThe Brain Interprets the Messages
Received to Determine an Output
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The Pain Experience

• Somatic
• Psychological
• Attention
• Anxiety
• Expectation
• Meaning of pain
• Social
• Provides context to the pain

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Patient and Clinician Education

• What effect will each of these (listed on
  previous slide) influences have on the perceived
  threat?
• CRPS

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Change in the BrainRemember the Homunculus?

• Proprioceptive representation of pained part
  changes in primary somatosensory cortex1

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Homunculus

• Skin and soft tissue representation
• Change in representation of parts of the brain
• Example phantom limb pain4
• Use-dependent brain2
• Demand more of a part, representation in the
  brain will be bigger ex. musicians

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How persistent pain develops

• Tissue injury may not be present pain continues
• Continued input sensitizes central neurons
• Pain can occur without tissue damage

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Brain Imaging
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SOOOOHow can we help our patients with
persistent pain?

• Its time for lab..

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References

• 1Moseley GL. Reconceptualizing pain according to
  modern pain science. Phys Ther Reviews.
  200712169-178.
• 2Butler D, Moseley GL. Explain Pain. Adelaide
  NOI Group Publishing, 2003.
• 3Melzack R. Evolution of the neuromatrix theory
  of pain. The Prithvi Raj Lecture Presented at
  the Third World Congress of World Institutes of
  Pain, Barcelona 2004. Pain Practice.
  20055(2)85-94
• 4Colapinto J. Brain games The Marco Polo of
  neuroscience. The New Yorker. May 3, 2009.