Neuropathic Pain, Pain Matrix Dysfunction, and Pain Syndromes Flashcards
In neuropathic pain, pain matrix dysfunction, and pain syndromes pain is not a warning of tissue injury, rather it is a _____
disease
What is neuropathic pain?
Pain arising as a direct consequence of a lesion or disease affecting the somatosensory system
What genetic code predisposes someone to develop neuropathic pain?
Individuals with genetic codes that produce less of the enzyme that regulates the levels of catecholamine and encephalin are twice as likely to develop neuropathic pain as those who produce more of the enzyme
What are the 4 symptoms of neuropathic pain?
- Paresthesia
- Dysesthesia
- Allodynia
- Secondary Hyperalgesia
What is parasthesia?
a painless abnormal sensation (tingling or prickling) in the absence of nociceptor stimulation
What is dysesthesia?
unpleasant abnormal sensation (buring pain or shooting electrical sensations), either evoked or spontaneous
What is allodynia?
pain evoked by a stimulus that normally would not cause pain
What is secondary hyperalgesia?
excessive sensitivity to stimuli that are normally mildly painful in uninjured tissue
What are the 4 Mechanisms for Neuropathic Pain?
- Ectopic foci
- Ephaptic transmission
- Central sensitization
- Structural reorganization
Describe the mechanism of ectopic foci
When myelin is damaged, signals from the exposed axon stimulate excessive production of mechanosensitive and chemosensitive ion channels. These channels are inserted into the demyelinated membrane, producing abnormal sensitivity to mechanical and chemical stimuli. The demyelinated regions take on a new, pathologic role of generating action potentials in addition to the normal role of conducting action potentials.
How may ectopic foci contribute to the development of pain syndromes?
The sensitivity of ectopic foci to circulating catecholamines may contribute to the development of pain syndromes
Where and why does ephaptic transmission occur?
It occurs in demyelinated regions due to a lack of insulation between neurons
What is central sensitization?
Excessive responsiveness of central neurons
What does central sensitization develop in response to?
Ongoing nociceptive input, but it even persists after the peripheral injury has healed
Central sensitization is created by what?
An increased availability of excitatory transmitters and an increased number of excitatory receptors
What are 4 cellular changes that reflect central sensitization?
- increased spontaneous activity
- increased responsiveness to afferent inputs
- prolonged afterdischarge in response to repeated stimuli
- expansion of receptive fields
What does prolonged central sensitization lead to?
rewiring of connections in the CNS
What structural changes occur in the dorsal horn?
Withdrawal of C-fiber axon terminals from the dorsal horn and growth of A(beta)-fiber axons into regions of the spinal cord that normally receives only C-fiber terminals
What are the 3 sites in which neuropathic pain can arise from abnormal neural activity?
- Periphery (e.g., nerve compression in carpal tunnel syndrome)
- CNS in response to deafferentation
- Dorsal horn
What does injury or disease of the peripheral nerves often result in?
sensory abnormalities
What do complete nerve resections result in?
a lack of sensation from that nerve’s receptive field
What do partially damaged nerve resections result in?
allodynia and sensations similar to an electric shock
What does avulsion of dorsal roots from the spinal cord produce?
Deafferentation and causes people to feel burning pain in the area of sensory loss