Mechanisms of pain Disclaimer: This presentation contains information on the general principles of pain management. This presentation cannot account for individual variation among patients and cannot be considered inclusive of all proper methods of care or exclusive of other treatments. It is the responsibility of the treating physician, or health care provider, to determine the best course of treatment for the patient. Treat the Pain and its partners assume no responsibility for any injury or damage to persons or property arising out of or related to any use of these materials, or for any errors or omissions. Last updated on January 12, 2015

Objectives for this module Discuss the ways pain can be characterised Duration Mechanism Origin Situation

Characterisations of pain Pain can be described by its: Duration – acute or chronic Mechanism – nociceptive or neuropathic Origin – somatic or visceral Situation – incidental pain, breakthrough pain, procedural pain Beating Pain, 2nd Ed. APCA (2012)

Different mechanisms of pain Why are they important? Pathophysiology is different Presentation is different Management is different

Duration: acute vs. chronic pain Acute pain Presentation: characterized by help-seeking behavior such as crying and moving about in a very obvious manner Cause: definite injury or illness Signs/symptoms: Definite onset with limited and predictable duration Clinical signs of sympathetic over-activity: tachycardia, pallor, hypertension, sweating, grimacing, crying, anxious, pupillary dilation Example: trauma, surgery, or inflammation Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013)

Duration: acute vs. chronic pain Presentation: Patients may not show signs of distress seen in acute pain Cause: chronic pathological process Under-treatment of acute pain can lead to changes in the central nervous system that result in chronic pain Signs/symptoms: Gradual or vague onset Continues and may become progressively more severe Patient may appear depressed and withdrawn Usually no signs of sympathetic over-activity Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013)

Mechanism: nociceptive pain Nociceptive pain: caused when nerve receptors called nociceptors are irritated. Nociceptors exist both internally (visceral) and externally (somatic) Indicates that nerve pathways are intact Beating Pain, 2nd Ed. APCA (2012); Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013).

Nociceptive pain: somatic pain Somatic pain: stimulation of nociceptors in the skin, soft tissues, muscle, or bone Pain usually is in a particular location Aching, throbbing, or persistent pain Causes: bone or soft tissue infiltration Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013)

Nociceptive pain: visceral pain Visceral pain: stimulation of nociceptors in internal organs and hollow viscera organs Pain is often not in a single location Described as pressure, cramping, or squeezing pain Causes: blockage, swelling, stretching, or inflammation of the organs from any cause Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013)

Mechanism: neuropathic pain Neuropathic pain: caused by damage to nerve pathways Described as burning, prickling, stinging, pins and needles, insects crawling under skin, numbness, hypersensitivity, shooting, or electric shock Causes: infiltration by cancer, HIV infection, or herpes zoster, drug-related peripheral neuropathy, central nervous system injury, or surgery Introductory Palliative Care Course for Health Care Professionals (Uganda). PCAU/MOH

Situation Incident pain – occurs only in certain circumstances (e.g. after a particular movement) Breakthrough pain – a sudden, temporary flare of severe pain that occurs on a background of otherwise controlled pain Procedural pain – related to procedures or interventions Beating Pain, 2nd Ed. APCA (2012)

Assessment Jane has come to your clinic with pain she’s describing as constant shooting pain in her feet for the past four days. How would you classify her pain? A. Procedural pain B. Chronic, visceral pain C. Acute, neuropathic pain D. Acute, incident pain Answer C: Beating Pain, 2nd Ed. APCA (2012)

Take home message Knowing the differences in the mechanisms of pain is important to adequately and appropriately treat the pain

References African Palliative Care Association. Beating Pain: a pocketguide for pain management in Africa, 2nd Ed. [Internet]. 2012. Available from: http://www.africanpalliativecare.org/images/stories/pdf/beating_pain.pdf African Palliative Care Association. Using opioids to manage pain: a pocket guide for health professionals in Africa [Internet]. 2010. Available from: http://www.africanpalliativecare.org/images/stories/pdf/using_opiods.pdf Amery J, editor. Children’s Palliative Care in Africa [Internet]. 2009. Available from: http://www.icpcn.org/wp-content/uploads/2013/08/Childrens-Palliative-Care-in- Africa-Full-Text.pdf Kopf A, Patel N, editors. Guide to Pain Management in Low-Resource Settings [Internet]. 2010. Available from: http://www.iasp- pain.org/files/Content/ContentFolders/Publications2/FreeBooks/Guide_to_Pain_ Management_in_Low-Resource_Settings.pdf The Palliative Care Association of Uganda and the Uganda Ministry of Health. Introductory Palliative Care Course for Healthcare Professionals. 2013.