Transcript Document

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 = “reporters”2 keeping
track of the body’s 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
messengers”1)
 Powerful chemicals
(stories) reverse flow
of ions and therefore
can stop signals
Rethinking the Brain’s 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
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 highthreshold and WDR neurons
 Expansion of receptive fields in central neurons
common
 As pain persists, neurons in brain that
induce pain become sensitized
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?
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 tissues…1
Neuromatrix Theory
The Brain Interprets the Messages
Received to Determine an Output
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
Change in the Brain:
Remember 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 brain”2
 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
SOOOO…How can we help our
patients with persistent pain?
 It’s time for lab…..
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References
GL. Reconceptualizing pain according to
modern pain science. Phys Ther Reviews. 2007;12:169178.
 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. 2005;5(2):85-94
 4Colapinto J. Brain games: The Marco Polo of
neuroscience. The New Yorker. May 3, 2009.

1Moseley
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