Putting Pain in a New Perspective, Or…

1. Putting Pain in a New Perspective, Or… Mary Christenson, PT, PhD DPT 781 O

2. 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”

3. 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

4. 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.

5. 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?

6. 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

7. 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?

8. 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

9. 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 Rethinking the Brain’s Involvement

10. 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

11. 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

12. 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?

13. Multiple Sites within the Brain – Decision-Making Power • Brain has billions of neurons – each neuron can connect with up to 5000 other neurons

14. At first glance: Is the yellow panel in front or back? http://www.bing.com/images/search?q=3+d+box+optical+illusion&go=&form=QBIR&qs=n&sk=#focal=aa51b477d526faca84a9a39bfdf0456a&furl=http%3A%2F%2Fwww.at-bristol.org.uk%2Fassets%2Fimages%2Fillusions%2F11.%2520The%2520Necker%2520Cube.jpg

15. 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

16. 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

17. It is the perception of the threat that determines the output, not the tissue damage itself or threat to the tissues…1Neuromatrix TheoryThe Brain Interprets the Messages Received to Determine an Output

18. The Pain Experience • Somatic • Psychological • Attention • Anxiety • Expectation • Meaning of pain • Social • Provides context to the pain

19. Patient and Clinician Education • What effect will each of these (listed on previous slide) influences have on the perceived threat? • CRPS

20. Proprioceptive representation of pained part changes in primary somatosensory cortex1 Change in the Brain:Remember the Homunculus?

21. 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

22. How persistent pain develops • Tissue injury may not be present – pain continues • Continued input sensitizes central neurons • Pain can occur without tissue damage

23. Brain Imaging

24. SOOOO…How can we help our patients with persistent pain? • It’s time for lab…..

25. References • 1Moseley GL. Reconceptualizing pain according to modern pain science. Phys Ther Reviews. 2007;12:169-178. • 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. 2005;5(2):85-94 • 4Colapinto J. Brain games: The Marco Polo of neuroscience. The New Yorker. May 3, 2009.