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Putting Pain in Perspective: Pain Matters

Putting Pain in Perspective: Pain Matters. Mary Christenson, PT, PhD DPT 781 O Fall 2010. American Pain Foundation. Virtual March on Washington Launches September 1, 2010 September Pain Awareness Month is rapidly approaching!. A Story.

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Putting Pain in Perspective: Pain Matters

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  1. Putting Pain in Perspective: Pain Matters Mary Christenson, PT, PhD DPT 781 O Fall 2010

  2. American Pain Foundation Virtual March on Washington Launches September 1, 2010 September Pain Awareness Month is rapidly approaching!

  3. A Story • Mailis-Gagnon A, Israelson D. Beyond Pain: Making the Mind-Body Connection. University of Michigan Press; 2005:98. • What do you want to learn in this course? http://www.cvshealthresources.com/Imagebank/Articles_images/chronic-pain.jpg

  4. Who/What Is Affected by Persistent Pain? • Individual • ADLs • Self-esteem • Confidence, other? • Family • Friends • Work environment • Society • How will this present in the clinic?

  5. Reflection • Who treats persistent pain? • Why is the study of pain important? • What do you currently know about the treatment of persistent pain?

  6. Pain Defined • “An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” 2

  7. Statistics • One out of six Americans, minimally, live with chronic pain (American Chronic Pain Association) • 20% globally have pain longer than 3 months 3 • ~$100 billions/year costs of persistent pain (AACPI - American Alliance of Cancer Pain Initiatives ) • $61.2 billion/year lost business income due to employees pain – only included musculoskeletal problems6

  8. Statistics (continued) • ~50 million Americans have persistent pain (American Pain Foundation) • Headaches are the most common type of pain (National Headache Foundation) • Elderly : • Community-dwelling – up to 50% c/o pain • Institutionalized – 71-83% c/o of at least one source of pain4

  9. Terminology • Acute Pain • Occurs with tissue damage or potential damage = a symptom • Protects from tissue damage and or until healing has occurred • Persistent Pain (Chronic Pain) • Extends beyond normal tissue healing time, and/or • Causes challenges greater than expected from tissue injury or medical findings, and/or • Occurs without known tissue damage

  10. Terminology • Hyperalgesia • Hyperpathia • Allodynia • Neurogenic pain • Neuropathic pain • Nociceptor • Nociception • Nociceptive pain • Sensitization • Peripheral • Central http://static.disaboom.com/content/images/articles/thumbnail/chronic-pain-with-nmd-is-und_thumbnail1.jpg

  11. http://www.painfoundation.org/

  12. Models of Pain • Historical • Specificity Theory • Separate nerve endings for each type of sensation (temperature, touch, pain) • Challenged: Phantom limb pain? Blockage of pain pathways? • Pattern Theory • Pain recognized by “sense organs” in skin • Consists of signals in the CNS • Sensation is a learned event – no specific pathways for each sensation

  13. Models (continued) • Gate Control Theory (Melzack and Wall, 1965) • Physiological and psychological components of pain • Nerve ending signals are modulated in the spinal cord • Large (non-nociceptor) and small (nociceptor) diameter afferent signals to the substantia gelatinosa (SG) and T cell • T cell initiates consequences of pain • SG cells are inhibitory to the T cell • Nociceptor signals inhibit the SG neurons, therefore allowing pain signals to continue • Increased signals from large diameter fibers results in increased firing of SG neurons, which ultimately decreases firing of T-cells (Result?) (Clinical application?) • System under control of supraspinal sites that affect outcomes • Challenges

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

  15. Gate Control Theory (continued) • This theory resulted in recognition that “pain is a CNS phenomenon, that treatments for pain must be aimed not only at the peripheral nervous system but also at modulating the CNS, and that pain is multidimensional.” 2

  16. Models (continued) • Biomedical Model • Biopsychosocial Model (conceptual model by the American College of Physicians) • Nociception • Pain • Pain Appraisal • Pain Behaviors • Social Roles for Pain and Illness

  17. Biopsychosocial Models of Pain http://www.continuingedcourses.net/active/courses/images/course033-image002.jpg

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

  19. Peripheral Primary Afferent • Nociceptors fire in response to a noxious stimulus • Mechanical • Thermal • Chemical

  20. Peripheral Nerve Fiber Types Letter System http://www.unmc.edu/physiology/Mann/mann12.html

  21. Peripheral Nerve Fiber Types Roman Numeral System II = Aβ ; III = Aδ ; IV = C http://www.unmc.edu/physiology/Mann/mann12.html

  22. Peripheral Receptors • Ia: muscle spindle • Ib: Golgi tendon organ • II: Meissner corpuscle, Merkel’s cell, Pacinian corpuscle, Ruffini ending, hair follicle, Paciniform endings, muscle spindle • III: Free nerve endings (noxious stim) • IV: Free nerve endings (noxious stim)

  23. Free Nerve Ending

  24. Silent Nociceptors • ~1/3 of nociceptors in skin, joints or viscera do not respond to stimulus until inflammation = “silent nociceptors” • May be activated by mediators such as prostaglandins that are released during inflammation • Increases pain response

  25. 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

  26. Neuronal Activators of Pain • Neuropeptides • Opioids • Glutamate • Ion Channels

  27. Non-neuronal Activators of Pain • Inflammatory processes cause the release of factors that can result in activating afferent nerves • Serotonin released from platelets • Bradykinin released plasma • Prostaglandins released from arachidonic acid cascade • Cytokines released by macrophages • Others: mast cells, neutrophils, T and B cells

  28. Structures of Pain http://journals.prous.com/journals/dnp/20041703/html/dn170172/images/Block_f1.jpg

  29. Physiology of Pain

  30. Central Mechanisms • Spinal Cord • Laminae I-VI make up the dorsal horn • Sensory afferents terminate (majority) on “2nd neuron” • Noxious information from skin: I, II, V (primarily) • Noxious information from muscles/joints: I (primarily) • Interneurons • Afferents from skin, joints, muscles, viscera may terminate on one neuron – referred pain?

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

  32. 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 – referred pain?

  33. 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?

  34. Potential Influences: Hyperalgesia(found in spinal cord) • Can produce hyperalgesia • Glial cells • Neurotransmitters – Spinal Cord • Glutamate • Substance P • Can reduce hyperalgesia • Adenosine • GABA

  35. Pain Sensory Pathways: Spinal Cord to Brain • Spinothalamic Tract • Transmits nociceptive pain up through the thalamus (VPL nucleus and medial thalamic nuclei) to higher centers • VPL to 1o and 2o somatosensory cortex: location, duration quality, and intensity of pain • Medial thalamic to anterior cinglate, etc.: “unpleasantness” of pain • Spinomesencephalic and Spinoreticular Tracts • Transmits to midbrain/brainstem respectively • Integrates information with areas involved in descending inhibition, facilitation, and autonomic pain responses

  36. Thalamus and Cortex • Thalamus • Integrate information from peripheral noxious stimulation • Cortex • S1 and S2: increased blood flow noted to these areas with painful stimuli • Homunculus (more to come) • Anterior cingulate cortex • Many other centers (to be continued)

  37. Brainstem Centers • Contains centers that contribute facilitation and or inhibition signals • A balance between all brain/brainstem signals determines pain perception • Other brain influences? • PAIN IS AN OUTPUT

  38. Measures of Pain

  39. Measures of Pain

  40. Associations • American Academy of Pain Management • American Pain Foundation • American Pain Society • American Chronic Pain Association • International Association for the Study of Pain (IASP)

  41. References • 1 Mailis-Gagnon A, Israelson D. Beyond Pain: Making the Mind-Body Connection. University of Michigan Press; 2005:98. • 2 Sluka KA, ed. Mechanisms and Management of Pain for the Physical Therapist. Seattle, WA: IASP Press; 2009. • 3 Butler DB, Moseley L. Explain Pain. Adelaide, Australia: Notgroup Publications; 2003. • 4 Galieze L. Chronic Pain in Elderly People. Pain. 1997;70(1):3-14. • 5 Marchand F, Perretti M, McMahon SB. Role of the immune system in chronic pain. Nature Reviews/Neuroscience. 2005;6:521-532. • 6 JAMA. 2003;290:2443-2454.

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