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Speaking of pain: syndromes and terminology (Proceedings)

Why Pain Terminology?

You can never become good at pain management without understanding basic pain pathways. You will have trouble understanding pain pathways without understanding the terminology used to describe them.

Nerves, Receptors, and Neurons

     • A-Alpha are proprioceptors that detect muscle tension and joint position
     • A-Beta Soft touch fibers
     • A-Delta Mechanoreceptors for hard touch, lancing pain
     • C Mechanoreceptors and transmit cold, heat and capsican.
     • Afferent Fibers carry signals toward the brain
     • Efferent Fibers carry signals toward the periphery
     • Inhibitory Neurons live in the dorsal horn of the spinal cord and are excited by antinociceptive periaquaductal grey stimulation
     • Mechanoreceptors Nociceptors that respond to pressure
     • Chemonociception is the response to chemical stimuli such as acid or capsaicin
     • Nociceptive Neurons are located within the CNS and receive input from nerve fibers

Pain Syndromes and Conditions causing increased sensitivity

     • Allodynia When normally non-painful stimuli causes pain
     • Hyperalgesia When painful stimuli causes more pain than it should
     • Hypersensitivity Refers to both allodynia and hyperalgesia
     • Hyperpathia When painful stimuli causes pain of longer duration than it should
     • Hyperkinesis Pin-prick induced itching sensations
     • Microglia A macrophage located within the CNS that plays an important role in hyperalgesia and allodynia
     • Central Sensitization is the increased sensitization of second order neurons (the second neuron to carry a signal) in the dorsal horn leading to increased sensitivity to pain.
     • Wind-up is a progressive increase in action-potential output from dorsal horn neurons elicited during the course of repeated nociceptor stimuli. This leads to an increase in pain during each successive stimulus even though the stimulus intensity does not change.
     • Peripheral sensitization is often found as a result of chronic atopy which causes and increase in nerve fiber density and hence, painful perceptions.
     • Radiculopathy/Polyradiculopathy is pain caused by the
     • compression of nerve root(s). Usually seen with intervertebral disc disease

Syndromes and Conditions Causing Decreased Sensitivity

     • Dysathesia is an unpleasant but non-painful sensation
     • Hypoalgesia is when the sensation evoked by a stimulus is weaker than normal
     • Parasthesia is an abnormal non-painful sensation

Spinal Cord Structures

     • Dorsal Horn The dorsal area of gray matter in the spinal cord that receives sensory information
     • Dorsal Root Ganglion is a nodule on a dorsal root that contains cell bodies of neurons in afferent spinal nerves.
     • Lamina are subdivisions of the dorsal horn, laminae I, II, III, and IV are of special interest in the conduction of pain signals
     • Epidural/Intrathecal Space The outermost layer of the spinal cord, outside the dura mater
     • Spinothalamic Tract A sensory tract starting in the spinal cord and going to the thalamus

Brain Structures

     • Don't try to remember them
     • Complex interaction of parts of brain
     • The Amygdala is part of the Limbic System which also involves emotions such as stress and anxiety. The shared responsibilities of the amygdala often results in emotional responses secondary to painful events.
     • Anterior and Posterior Cingulate Cortex
     • Amygdala
     • Basal Ganglia
     • Hypothalamus
     • Primary and Secondary Motor Cortex
     • Periaqueductal Gray
     • Dorsolateral Pons
     • Prefrontal Cortex
     • Posterior Parietal Cortex

Mechanisms of Acute Pain

     • Transduction is the transformation of energy from the surgical injury into neural impulses
     • Peripheral Sensitization is a decrease in the nociceptor threshold due to changes in the transducers or due to an increase in the excitability of the terminal membrane, initiated by sensitizing agents
     • Conduction is the propagation of electrical impulses in primary afferent nerves to the spinal cord
     • Transmission is the transmission of pain signals from primary afferents to secondary nociceptive neurons in the dorsal horn via release and uptake of neurotransmitters
     • Inhibition is the regulation or focusing of central neuronal excitation through activation of segmental and descending inhibitory neurons.
     • Central Sensitization is the enhanced responsiveness of central pain transmission neurons due to wind-up, facilitated synaptic responses and depressed inhibition.
     • Modification is the long term or permanent alterations in both primary sensory neurons and and central pathways, due to altered gene regulation, altered connectivity and cell death.
     • Perception is the recognition of the final pain signal in the somatosensory cortex and other areas of the brain.

Inflammatory Mediators "The Bad Guys"

     • ATP When released from damaged cells causes pain and inflammation
     • Bradykinin Released from damaged cells and plays role in acute and chronic pain
     • Low pH/Acidic Conditions have direct effect on sensory nerves, causing pain
     • Nitric Oxide Plays role in inflammatory hyperalgesia and pain. Has possible NMDA effect
     • Norepinephrine Causes inflammation mostly through increased release of prostaglandins
     • Serotonin is a neurotransmitter that causes hyperalgesia
     • Substance P is a neurotransmitter associated with inflammation and pain
     • Prostaglandins/Prostanoids Inflammatory agents that act on the CNS and periphery
     • Glutamate a neurotransmitter closely associated with the NMDA pathway
     • Cytokines are secreted by glial cells and cause chronic inflammation
     • Tumor Necrosis Factor is a type of Cytokine

Endogenous Opioid Peptides "The Good Guys"

All work on Mu Delta and Kappa receptors, depending on the peptide

     • Enkephalin
     • Endorphin
     • Dynorphin
     • Endomorphin
     • Nociceptin

Pain Treatments

     • Medical Acupuncture is the process of placing a needle near a nerve, blood vessel, muscle junction or fascial plane in order to cause a known neurophysiological effect
     • Dry Needling is the process of placing a needle into the myofascial trigger point in the taut band of an effected muscle
     • TENS Transcutaneous Electric Nerve Stimulation is the use of specific frequencies and amplitudes of electricity to decrease pain
     • PENS Percutaneous Electric Nerve Stimulation is like TENS but the current is applied to an acupuncture needle that is penetrating the skin
     • Transcutaneous Electrophoresis The movement of medication through the skin using electrical current
     • Stem Cell Therapy The harvesting of stem cells for transplantation into joints for the purpose of causing new cartilage growth
     • Platelet Rich Plasma Injections The injection of platelet rich plasma into damaged tendons and ligaments for its ant-inflammatory and healing properties

Types of Pain

     • Arthritis/Osteoarthritis Joint pain
     • Rheumatoid Arthritis Joint pain secondary to immune issues
     • Neuralgia Nerve pain without stimulation of the associated nociceptor
     • Neuropathic Pain is secondary to a disease affecting the somatosensory system. e.g. diabetic neuropathy
     • Neuritis Damage to nerves of the peripheral nervous system, usually a compression neuritis from trauma. An example is carpal tunnel syndrome in humans
     • Polyneuropathies when peripheral neuropathies occur throughout the body simultaneously. Examples are demyelination or vincristine toxicity
     • Radiculopathy/Radicular pain Nerve pain secondary to compression or impingement of a spinal nerve root.

Acute Pain Assessment

     • Numeric Analog Scale
     • Numeric Rating Scale
     • Visual Analog Scale
     • University of Melbourne Pain Scale
     • Glasgow Short-Form Composite Scale
     • Colorado State University Acute Pain Scale - The one i like best
     • Canine and Feline scales
     • Many others out there. not a single one is validated

Chronic Pain Scale

     • Even worse. Problems:
          o Correlating clinical observations with owner observations
          o Ability to even know pain is present
     • Colorado State University Chronic Pain Scale
          o Good for clinical observations. Not so good for owner observations