Neuropathic Pain, Pain Matrix Dysfunction, and Pain Syndromes Flashcards
What are the four types of chronic pain?
- Nociceptive (mechanical, cancer, burns)
- Neuropathic (nerve entrapment, central pain, neuropathy)
- Pain matrix dysfunction (fibromyalgia, chronic whiplash, headache)
- Pain syndromes (CRPS, chronic LBP syndrome)
pain arising as a direct consequence of a lesion or disease affecting the somatosensory system, which can be anywhere in the somatosensory system (mechanical LBP, cancer, arthritis, burns)
Neuropathic pain
Individuals with genetic codes that produce less of the enzyme that regulates the levels of _______ and ______ are twice as likely to develop neuropathic pain as those who produce more of the enzyme
catecholamine; encephalin
painless abnormal sensation in the absence of nociceptor stimulation (tingling sensations)
Paresthesia
unpleasant abnormal sensation, either evoked or spontaneous (painful)
Dysethesia
pain evoked by a stimulus that normally would not cause pain (usually light touch)
Allodynia
excessive sensitivity to stimuli that are normally mildly painful in uninjured tissue
Secondary hyperalgesia
What are the symptoms of neuropathic pain?
- Paresthesia
- Dysesthesia
- Allodynia
- Secondary hyperalgesia
What are the 5 mechanisms that produce neuropathic pain?
- Ectopic foci
- Ephaptic transmission
- Central sensitization
- Structural reorganization
- Altered top-down modulation
When myelin is damaged, signals from the exposed axon stimulate excessive production of mechanosensitive and chemosensitive ion channels; Channels are inserted into the demyelinated membrane, producing abnormal sensitivity to mechanical and chemical stimuli; Demyelinated regions take on the new, pathologic role of generating action potentials in addition to the normal role of conducting action potentials
Ectopic foci
Cross-talk between axons in regions of demyelination
Ephaptic Transmission
Test where you tap along a nerve, the point where a nerve is injured becomes more sensitive; region where schwann cells are damaged, so insulation between axons is lost and one axon may stimulate its neighbor
Tinel’s sign
Occurs in the CNS; greater peripheral nerve sensitization occurs, so also has greater sensitization in CNS, resulting in increased perception of pain; as intense pain is prolonged, the CNS changes and everything becomes painful, no matter what the peripheral input is; pain does not reverse back to normal input
Central sensitization
Loss of nociceptive neuron from the body; sprouting occurs where touch sensation neuron makes connections with neurons that carry nociceptive information to the brain; hard to get back to normal
Structural reorganization
Antinociceptive pathways are decreased/inhibited/lost, so pain stimulus is increased because pronociceptive signals are not inhibited
Pain matrix dysfunction
Neuropathic pain arise from abnormal activity in the
- Periphery (e.g., nerve compression in carpal tunnel syndrome)
- CNS in response to deafferentation
- Dorsal horn
__________ generation of neuropathic pain can occur as a result of:
- Injury or disease of the peripheral nerves often results in sensory abnormalities.
- Complete nerve resection results in a lack of sensation from that nerve’s receptive field.
- Partial damage can result in allodynia and sensations similar to an electric shock.
Peripheral
What are the peripheral abnormalities causing neuropathic pain?
- Development of ephaptic transmission that occurs in demyelinated regions
- Ectopic foci in an injured nerve that occurs at the nerve stump, in areas of myelin damage, or in dorsal root ganglion somas
Central response to _______:
Occurs when a nerve loses its input so the receiving neuron becomes more sensitive to any stimulus; Avulsion of dorsal roots from the spinal cord produces ___(same word)___ and causes an individual to feel burning pain in the area of sensory loss; Neurons in the CNS may become abnormally active when peripheral sensory information is completely absent
Deafferentation
refers to individuals who have had a limb amputated but experience sensations that seem to originate from the missing limb
Phantom limb sensation
Phantom sensation that is painful; reports of this are more rare
Phantom pain
- must be differentiated from residual limb pain; treatment for residual limb pain is different than for phantom limb pain
caused by a lesion of the CNS and is usually localized to the area of the body deafferented by the lesion; refers to burning, shooting, aching, freezing, or tingling pain
neuropathic central pain
the thalamus may be the site of pain generation because after a SCI, the neurons in the VPL thalamic nucleus are spontaneously active without input from the spinal cord
SCI central pain
Where does pain occur due to MS central pain?
Depends on the location of the lesion
Top-down regulation of pain is disturbed when this occurs; Antinociception is reduced and/or pronociception is intensified; the result is increased pain; Fibromyalgia, episodic tension-type headache, migraine, and chronic whiplash-associated disorder are all the rest of this
pain matrix dysfunction
What are the criteria for episodic tension-type headache?
- Mild-to-moderate pain, usually bilateral
- Lasting 30 minutes to 7 days
- Not aggravated by physical activity
- Not associated with nausea or vomiting
- Photophobia or phonophobia, but not both, may accompany the headache.
- Mechanism appears to be supersensitivity to nitric oxide
What are two pain syndromes that involve other systems in addition to the pain system?
- Complex regional pain syndrome - involves the somatosensory, autonomic, and motor systems
- Chronic low back pain syndrome - involves muscle guarding, disuse, and abnormal movements
Response to injured body part due to pt not using affected part; increased levels of inflammatory neurochemicals in the periphery, partial denervation of epidermis and upper dermis, impairment of sympathetic regulation of blood flow and sweating, sensitization, and cortical reorganization; early intervention has best outcome; intensive PT often required; some cases are intractable
Complex regional pain syndrome
decreased endurance of abdominal and back muscles
Chronic low back pain
What is the surgical treatment of chronic pain?
dorsal rhizotomy
-often fails in practice; only short term
Why does dorsal rhizotomy fail?
may be the result of CNS changes in response to the original maintained pain or to pain-mediating fibers traveling in the dorsal columns
Where does acetaminophen work?
peripheral nervous system
Where do selective norepinephrine reuptake inhibitors work?
- Dorsal horn of spinal cord
2. Cerebral cortex
Where do cannabinoids?
Raffe neuclei (Rostral ventromedial medulla)
Where do SSRIs work?
cerebral cortex
where do NSAIDs work?
- PNS
2. Periaqueductal gray
Where do opioids work?
- Dorsal horn
- Raffe nuclei (Rostral ventromedial medulla)
- Periaqueductal gray
- Cerebral cortex
What three Ds must therapists address for chronic pain?
- Distress
- Disuse
- Disability
What psychologic interventions may decrease activation of pain systems and improve coping skills?
- relaxation (breathing, m. relaxation)
- biofeedback
- imagery
- cognitive behavioral therapy
any genuine psychological or physiologic effect which is attributable to receiving a substance or undergoing a procedure, but is not due to the inherent powers of that substance or procedure
Placebo-associated improvement
Where do tricyclic antidepressants work?
- dorsal horn of SC
2. Cerebral cortex
Abnormal central processing of pain signals in both pain amplification and impaired defending inhibition; incr. levels of substance P and glutamate in SC; decreased pain inhibition from brainstem to dorsal horn
fibromyalgia
