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Putting Pain in Putting Pain in Perspective: Perspective: Pain MattersPain Matters

Mary Christenson, PT, PhDMary Christenson, PT, PhD

DPT 781 ODPT 781 O

Fall 2010Fall 2010

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Virtual March on Washington Launches September 1, 2010

                                      September Pain Awareness Month is rapidly

approaching!

American Pain Foundation

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A StoryA Story

Mailis-Gagnon A, Mailis-Gagnon A, Israelson D. Israelson D. Beyond Beyond Pain: Making the Mind-Pain: Making the Mind-Body ConnectionBody Connection. . University of Michigan University of Michigan Press; 2005:98.Press; 2005:98.

What do you want to What do you want to learn in this course?learn in this course?

http://www.cvshealthresources.com/Imagebank/Articles_images/chronic-pain.jpg

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Who/What Is Affected Who/What Is Affected by Persistent Pain?by Persistent Pain?

IndividualIndividual ADLsADLs Self-esteemSelf-esteem Confidence, other?Confidence, other?

FamilyFamily FriendsFriends Work environmentWork environment SocietySociety

How will this present in the clinic?How will this present in the clinic?

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ReflectionReflection

Who treats persistent pain?Who treats persistent pain?

Why is the study of pain important?Why is the study of pain important?

What do you currently know about What do you currently know about the treatment of persistent pain?the treatment of persistent pain?

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Pain DefinedPain Defined

““An unpleasant sensory and An unpleasant sensory and emotional experience associated emotional experience associated with actual or potential tissue with actual or potential tissue damage, or described in terms of damage, or described in terms of such damage.” such damage.” 22

StatisticsStatistics

One out of six Americans, minimally, live One out of six Americans, minimally, live with chronic pain (American Chronic Pain with chronic pain (American Chronic Pain Association)Association)

20% globally have pain longer than 3 20% globally have pain longer than 3 months months 33

~$100 billions/year costs of persistent ~$100 billions/year costs of persistent pain (AACPI - American Alliance of Cancer pain (AACPI - American Alliance of Cancer Pain Initiatives )Pain Initiatives )

$61.2 billion/year lost business income $61.2 billion/year lost business income due to employees pain – only included due to employees pain – only included musculoskeletal problemsmusculoskeletal problems66

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Statistics (continued)Statistics (continued)

~50 million Americans have persistent ~50 million Americans have persistent pain (American Pain Foundation)pain (American Pain Foundation)

Headaches are the most common type Headaches are the most common type of pain (National Headache Foundation)of pain (National Headache Foundation)

Elderly :Elderly : Community-dwelling – up to 50% c/o painCommunity-dwelling – up to 50% c/o pain Institutionalized – 71-83% c/o of at least one Institutionalized – 71-83% c/o of at least one

source of painsource of pain44

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TerminologyTerminology

Acute PainAcute Pain Occurs with tissue damage or potential damage Occurs with tissue damage or potential damage

= a symptom= a symptom Protects from tissue damage and or until healing Protects from tissue damage and or until healing

has occurredhas occurred Persistent Pain (Chronic Pain)Persistent Pain (Chronic Pain)

Extends beyond normal tissue healing time, Extends beyond normal tissue healing time, and/orand/or

Causes challenges greater than expected from Causes challenges greater than expected from tissue injury or medical findings, and/ortissue injury or medical findings, and/or

Occurs without known tissue damageOccurs without known tissue damage

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TerminologyTerminology

HyperalgesiaHyperalgesia HyperpathiaHyperpathia AllodyniaAllodynia Neurogenic painNeurogenic pain Neuropathic painNeuropathic pain NociceptorNociceptor NociceptionNociception Nociceptive painNociceptive pain SensitizationSensitization

PeripheralPeripheral CentralCentral

http://static.disaboom.com/content/images/articles/thumbnail/chronic-pain-with-nmd-is-und_thumbnail1.jpg

1111http://www.painfoundation.org/

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Models of PainModels of Pain

HistoricalHistorical Specificity TheorySpecificity Theory

Separate nerve endings for each type of sensation Separate nerve endings for each type of sensation (temperature, touch, pain)(temperature, touch, pain)

Challenged: Phantom limb pain? Blockage of pain Challenged: Phantom limb pain? Blockage of pain pathways?pathways?

Pattern TheoryPattern Theory Pain recognized by “sense organs” in skinPain recognized by “sense organs” in skin Consists of signals in the CNSConsists of signals in the CNS Sensation is a learned event – no specific pathways Sensation is a learned event – no specific pathways

for each sensationfor each sensation

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Models (continued)Models (continued)

Gate Control Theory (Melzack and Wall, 1965)Gate Control Theory (Melzack and Wall, 1965) Physiological and psychological components of pain Physiological and psychological components of pain Nerve ending signals are modulated in the spinal cordNerve ending signals are modulated in the spinal cord

Large (non-nociceptor) and small (nociceptor) diameter Large (non-nociceptor) and small (nociceptor) diameter afferent signals to the substantia gelatinosa (SG) and T afferent signals to the substantia gelatinosa (SG) and T cell cell

T cell initiates consequences of painT cell initiates consequences of pain SG cells are inhibitory to the T cellSG cells are inhibitory to the T cell Nociceptor signals inhibit the SG neurons, therefore Nociceptor signals inhibit the SG neurons, therefore

allowing pain signals to continueallowing pain signals to continue Increased signals from large diameter fibers results in Increased signals from large diameter fibers results in

increased firing of SG neurons, which ultimately increased firing of SG neurons, which ultimately decreases firing of T-cells (Result?) (Clinical application?)decreases firing of T-cells (Result?) (Clinical application?)

System under control of supraspinal sites that affect System under control of supraspinal sites that affect outcomesoutcomes

ChallengesChallenges

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http://www.lupusuk.org.uk/images/latestnews/lwcpfig1.gif

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Gate Control Theory Gate Control Theory (continued)(continued)

This theory resulted in recognition This theory resulted in recognition that “pain is a CNS phenomenon, that “pain is a CNS phenomenon, that treatments for pain must be that treatments for pain must be aimed not only at the peripheral aimed not only at the peripheral nervous system but also at nervous system but also at modulating the CNS, and that pain is modulating the CNS, and that pain is multidimensional.” multidimensional.” 22

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Models (continued)Models (continued)

Biomedical ModelBiomedical Model Biopsychosocial Model (conceptual Biopsychosocial Model (conceptual

model by the American College of model by the American College of Physicians)Physicians) Nociception Nociception PainPain Pain AppraisalPain Appraisal Pain BehaviorsPain Behaviors Social Roles for Pain and IllnessSocial Roles for Pain and Illness

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http://www.continuingedcourses.net/active/courses/images/course033-image002.jpg

Biopsychosocial Models of Pain

1818http://www.painxchange.com.au/images/BiopsychosocialPain.png

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Peripheral Primary AfferentPeripheral Primary Afferent

Nociceptors fire in response to a Nociceptors fire in response to a noxious stimulusnoxious stimulus MechanicalMechanical ThermalThermal ChemicalChemical

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Letter System

Type of fiber

Diameter, micrometers

Conduction velocity, m/sec

General Function

A-alpha 13-22 70-120 alpha-motoneurons, muscle spindle primary endings, Golgi tendon organs, touch

A-beta 8-13 40-70 touch, kinesthesia, muscle spindle secondary endings

A-gamma 4-8 15-40 touch, pressure, gamma-motoneurons

A-delta 1-4 5-15 pain, crude touch, pressure, temperature

B 1-3 3-14 preganglionic autonomic

C 0.1-1 0.2-2 pain, touch, pressure, temperature, postganglionic autonomic

Peripheral Nerve Fiber Types

http://www.unmc.edu/physiology/Mann/mann12.html

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Roman Numeral System

Type of fiber

Diameter, micrometers

Conduction velocity, m/sec

General Function

Ia 12-20 70-120 muscle spindle primary endings

Ib 11-19 66-114 Golgi tendon organs

II 5-12 20-50 touch, kinesthesia, muscle spindle secondary endings

III 1-5 4-20 pain, crude touch, pressure, temperature

IV 0.1-2 0.2-3 pain, touch, pressure, temperature

Peripheral Nerve Fiber Types

http://www.unmc.edu/physiology/Mann/mann12.html

II = Aβ ; III = Aδ ; IV = C

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Peripheral ReceptorsPeripheral Receptors

Ia: muscle spindleIa: muscle spindle Ib: Golgi tendon organIb: Golgi tendon organ II: Meissner corpuscle, Merkel’s cell, II: Meissner corpuscle, Merkel’s cell,

Pacinian corpuscle, Ruffini ending, hair Pacinian corpuscle, Ruffini ending, hair follicle, Paciniform endings, muscle follicle, Paciniform endings, muscle spindlespindle

III: Free nerve endings (noxious stim)III: Free nerve endings (noxious stim) IV: Free nerve endings (noxious stim)IV: Free nerve endings (noxious stim)

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Free Nerve EndingFree Nerve Ending

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Silent NociceptorsSilent Nociceptors

~1/3 of nociceptors in skin, joints or ~1/3 of nociceptors in skin, joints or viscera do not respond to stimulus viscera do not respond to stimulus until inflammation = “silent until inflammation = “silent nociceptors”nociceptors”

May be activated by mediators such May be activated by mediators such as prostaglandins that are released as prostaglandins that are released during inflammationduring inflammation

Increases pain responseIncreases pain response

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Peripheral SensitizationPeripheral Sensitization

Increased responsiveness to stimuli Increased responsiveness to stimuli after initial injuryafter initial injury

Potential mechanisms:Potential mechanisms: Lower threshold to stimulusLower threshold to stimulus Increase in neuron activityIncrease in neuron activity Increase in area of receptor fieldsIncrease in area of receptor fields Increase in response to the same Increase in response to the same

stimulusstimulus

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Neuronal Activators of PainNeuronal Activators of Pain

NeuropeptidesNeuropeptides OpioidsOpioids GlutamateGlutamate Ion ChannelsIon Channels

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Non-neuronal Activators of Non-neuronal Activators of PainPain

Inflammatory processes cause the release Inflammatory processes cause the release of factors that can result in activating of factors that can result in activating afferent nervesafferent nerves Serotonin released from plateletsSerotonin released from platelets Bradykinin released plasmaBradykinin released plasma Prostaglandins released from arachidonic acid Prostaglandins released from arachidonic acid

cascadecascade Cytokines released by macrophagesCytokines released by macrophages Others: mast cells, neutrophils, T and B cellsOthers: mast cells, neutrophils, T and B cells

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Structures of PainStructures of Pain

http://journals.prous.com/journals/dnp/20041703/html/dn170172/images/Block_f1.jpg

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Physiology of Pain

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Central MechanismsCentral Mechanisms

Spinal CordSpinal Cord Laminae I-VI make up the dorsal hornLaminae I-VI make up the dorsal horn

Sensory afferents terminate (majority) on “2Sensory afferents terminate (majority) on “2ndnd neuron”neuron”

Noxious information from skin: I, II, V (primarily)Noxious information from skin: I, II, V (primarily) Noxious information from muscles/joints: I (primarily)Noxious information from muscles/joints: I (primarily)

InterneuronsInterneurons Afferents from skin, joints, muscles, viscera Afferents from skin, joints, muscles, viscera

may terminate on one neuron – referred pain?may terminate on one neuron – referred pain?

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Dorsal HornDorsal Horn

http://www.wdv.com/Cancer/Pain/Images/Anatomy1.gif

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Central SensitizationCentral Sensitization

Neurons in dorsal hornNeurons in dorsal horn High-threshold – respond to noxious stimHigh-threshold – respond to noxious stim Low-threshold – respond to innocuous stimLow-threshold – respond to innocuous stim Wide-dynamic-range (WDR) – respond to bothWide-dynamic-range (WDR) – respond to both

Tissue injury: increased sensitivity of high-Tissue injury: increased sensitivity of high-threshold and WDR neuronsthreshold and WDR neurons Expansion of receptive fields in central neurons Expansion of receptive fields in central neurons

common – referred pain?common – referred pain?

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SensitizationSensitization

Continued input from sensitized Continued input from sensitized nociceptors can maintain nociceptors can maintain sensitization of dorsal horn neuronssensitization of dorsal horn neurons Need to reduce peripheral input?Need to reduce peripheral input?

Sensitization of dorsal horn neurons Sensitization of dorsal horn neurons can also be maintained in absence of can also be maintained in absence of peripheral inputperipheral input Need to reduce central sensitization?Need to reduce central sensitization?

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Potential Influences: Potential Influences: HyperalgesiaHyperalgesia

(found in spinal cord)(found in spinal cord) Can produce hyperalgesiaCan produce hyperalgesia

Glial cellsGlial cells Neurotransmitters – Spinal CordNeurotransmitters – Spinal Cord

GlutamateGlutamate Substance PSubstance P

Can reduce hyperalgesiaCan reduce hyperalgesia AdenosineAdenosine GABAGABA

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Pain Sensory Pathways: Pain Sensory Pathways: Spinal Cord to BrainSpinal Cord to Brain

Spinothalamic TractSpinothalamic Tract Transmits nociceptive pain up through the thalamus Transmits nociceptive pain up through the thalamus

(VPL nucleus and medial thalamic nuclei) to higher (VPL nucleus and medial thalamic nuclei) to higher centerscenters

VPL to 1VPL to 1oo and 2 and 2oo somatosensory cortex: location, duration somatosensory cortex: location, duration quality, and intensity of painquality, and intensity of pain

Medial thalamic to anterior cinglate, etc.: “unpleasantness” Medial thalamic to anterior cinglate, etc.: “unpleasantness” of painof pain

Spinomesencephalic and Spinoreticular TractsSpinomesencephalic and Spinoreticular Tracts Transmits to midbrain/brainstem respectivelyTransmits to midbrain/brainstem respectively Integrates information with areas involved in descending Integrates information with areas involved in descending

inhibition, facilitation, and autonomic pain responsesinhibition, facilitation, and autonomic pain responses

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Thalamus and CortexThalamus and Cortex

ThalamusThalamus Integrate information from peripheral Integrate information from peripheral

noxious stimulationnoxious stimulation CortexCortex

S1 and S2: increased blood flow noted S1 and S2: increased blood flow noted to these areas with painful stimulito these areas with painful stimuli

Homunculus (more to come)Homunculus (more to come) Anterior cingulate cortexAnterior cingulate cortex Many other centers (to be continued)Many other centers (to be continued)

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Brainstem CentersBrainstem Centers

Contains centers that contribute Contains centers that contribute facilitation and or inhibition signalsfacilitation and or inhibition signals

A balance between all brain/brainstem A balance between all brain/brainstem signals determines pain perceptionsignals determines pain perception

Other brain influences?Other brain influences?

PAIN IS AN OUTPUTPAIN IS AN OUTPUT

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Measures of PainMeasures of Pain

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Measures of Pain Measures of Pain

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AssociationsAssociations

American Academy of Pain American Academy of Pain ManagementManagement

American Pain FoundationAmerican Pain Foundation American Pain SocietyAmerican Pain Society American Chronic Pain AssociationAmerican Chronic Pain Association International Association for the International Association for the

Study of Pain (IASP)Study of Pain (IASP)

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ReferencesReferences

1 Mailis-Gagnon A, Israelson D. 1 Mailis-Gagnon A, Israelson D. Beyond Pain: Making Beyond Pain: Making the Mind-Body Connectionthe Mind-Body Connection. University of Michigan . University of Michigan Press; 2005:98.Press; 2005:98.

2 Sluka KA, ed. 2 Sluka KA, ed. Mechanisms and Management of Pain Mechanisms and Management of Pain for the Physical Therapistfor the Physical Therapist. Seattle, WA: IASP Press; . Seattle, WA: IASP Press; 2009.2009.

3 Butler DB, Moseley L. 3 Butler DB, Moseley L. Explain PainExplain Pain. Adelaide, . Adelaide, Australia: Notgroup Publications; 2003.Australia: Notgroup Publications; 2003.

4 Galieze L. Chronic Pain in Elderly People. 4 Galieze L. Chronic Pain in Elderly People. Pain.Pain. 1997;70(1):3-14.1997;70(1):3-14.

5 Marchand F, Perretti M, McMahon SB. Role of the 5 Marchand F, Perretti M, McMahon SB. Role of the immune system in chronic pain. immune system in chronic pain. Nature Nature Reviews/NeuroscienceReviews/Neuroscience. 2005;6:521-532.. 2005;6:521-532.

6 6 JAMA.JAMA. 2003;290:2443-2454. 2003;290:2443-2454.