Chapter 19 - Pain

Questions

Define the following terms:

Nociceptive pain, neuropathic pain, postherepetic neuralgia, allodynia, dysesthesia, deafferentation pain , causalgia, substance P, hyperalgesia, fibromyalgia syndrome.
Nociceptive pain is pain due to direct activation of pain nerve fibers. This is they type of pain that results from tissue damage or inflammation.
Neuropathic pain is pain that is generated or sustained by activity in the nervous system. This can be peripheral, with excessive sensitivity of the pain nerve fibers or loss of large diameter sensory nerve fibers. It can also be central, related to changes in the excitability of pain neurons or decrease in normal inhibitory mechanisms.
Postherpetic neuralgia is continued pain and dysesthesias after resolution of an active Herpes zoster infection (shingles). This can be due to sensitized nerve fibers but also to loss of normal sensory fibers in the region.
Allodynia is a condition in which innocuous stimuli are perceived as painful.
Dysesthesia is a painful paresthesia.
Deafferentation pain refers to pain resulting from loss of normal large-fiber (touch and pressure) sensory input.
Causalgia is sustained pain and autonomic changes due to damage to nerve trunks.
Substance P, along with calcitonin gene-related peptide and neurokinin A, are peptide neurotransmitters for small-diameter nociceptive afferent fibers.
Hyperalgesia is the magnified perception of pain from a normally painful stimulus.
Fibromyalgia syndrome is an idiopathic condition of diffuse, chronic pain characterized by sensitivity of many muscles to normally innocuous stimulation.

19-1. What tissue components interact with nociceptive nerve fibers to produce pain?

19-1. Many tissue components interact with nociceptive fibers. These include: acid; potassium; ATP; bradykinin; histamine; prostaglandins; leukotrines; cytokines; Substance P; catecholamines, serotonin, and nerve growth factors. Some of these act by directly stimulating the axons and others sensitize the axon or trigger release of other algetic substances.

19-2. What are mechanisms of generation of neuropathic pain?

19-2. Neuropathic pain is pain that is generated or sustained by activity in the nervous system. This can be peripheral, with excessive sensitivity of the pain nerve fibers or loss of large diameter sensory nerve fibers. It can also be central, related to changes in the excitability of pain neurons or decrease in normal inhibitory mechanisms.

19-3. What is projected pain?

19-3. Projected pain is the perception of pain at more distal sites due to damage to a nerve along its course.

19-4. What is the mechanism of deafferentation pain?

19-4. Deafferentation pain refers to pain in a region lacking normal sensitivity. This probably occurs due to lack of normal modulation by normal sensory inputs but there is also evidence that damage to normal sensory pathways can decrease the activity of inhibitory systems of the brain and spinal cord.

19-5. How is sympathetically maintained pain recognized ?

19-5. Sympathetically-maintained pain is recognized by persistent changes in regional autonomic function (sweating, blood flow, temperature) along with signs of neurogenic inflammation and sustained pain. This may follow relatively minor injury.

19-6. What is "long-term potentiation"?

19-6. Long-term potentiation is the change that occurs in neuronal excitability due to high-intensity activation of convergent sensory pathways. This is associated with activation of certain glutamate channels (NMDA receptors) which permit calcium entry to the neuron with resultant sustained changes in the receptors expressed at the synapse (i.e., "pain memory").

19-7. What is the character of neuropathic pain?

19-7. Neuropathic pain is commonly described a shooting, stabbing, burning, or searing pain and it is often associated with allodynia. Pain is also commonly worse at night.

19-8. What are the theories for the etiology of fibromyalgia syndrome?

19-8. The various theories for the etiology of fibromyalgis have include: a primary sleep disorder; a subtle endocrine dysfunction; a subtle immune dysfunction; a mood disorder; a disorder of serotonin metabolism; a disorder of muscle metabolism; an unrecognized infectious condition; or a neurologic disorder. There is evidence of some genetic predilection, but the specific gene(s) are not known.

19-9. What kinds of treatments are available for fibromyalgia syndrome?

19-9. Education, certain medications, exercise, and cognitive/behavioral therapy form the cornerstone of treatment. The medications that have some value in this condition tend to be those employed in neuropathic pain and very slowly advancing levels of cardiovascular conditioning exercises are quite effective if the patient persists with the program.

19-10. Who is most likely to develop fibromyalgia syndrome?

19-10. This condition is about ten times more common in women and usually develops in middle ages.

19-11. What is the most important brain region with regard to suffering?

19-11. The medial part of the prefrontal cortex appears to be the primary site adding affective coloring to the noxious simulus (i.e., is the area that is mainly responsible for suffering).