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
What is deafferentation?
the interruption or destruction of the afferent connections of nerve cells
What is phantom pain?
Pain that seems to originate from the missing limb of amputees
What causes phantom pain?
The absence of sensory information from the amputated limb causes neurons in the central nociceptive pathways to become overactive
What is neuropathic central pain?
Pain that is described as a burning, shooting, aching, freezing, or tingling pain caused by a lesion of the CNS that is usually localized to the area of the body deafferented by the lesion
What is the site of pain after a spinal cord lesion? Why?
The thalamus, because the neurons in the VPL thalamic nucleus are spontaneously active without input from the spinal cord
Central pain occurs in 30% of people who have what pathology?
multiple sclerosis
What does small fiber neuropathy produce?
partial deafferentation and central sensitization
What 3 pathologies cause deafferentation pain?
- Postherpectic neurolgia
- Diabetic neuropathy
- Guillian-Barre syndrome
What happens when the pain matrix malfunctions?
Top-down regulation of pain is disturbed, antinociception is reduced, and pronociception is intensified. All of which result in increased pain
What are some examples of pathologies in which there is a disturbance of top-down regulation of pain?
- fibromyalgia
- episodic tension-type headache
- migraine
- chronic whiplash-associated disorder
What is the fundamental problem behind fibromyalgia?
Abnormal processing of pain information, resulting in perception of pain without any painful stimulus external to the nervous system
What is the primary symptom of fibromyalgia?
chronic widespread pain
How should you treat fibromyalgia?
- Aquatic therapy (with or without exercise)
- Individualized aerobic exercise and strength training
- A combination of OT/PT/cognitive therapy
What are the 4 criteria for episodic tension-type headache (ETTH)?
- Mild-to-moderate pain, usually bilateral
- Lasting 30 minutes to 7 days
- Not aggravated by physical activity
- Not associated with nausea or vomiting
What is the mechanism behind ETTH?
Supersensitivity to nitric oxide, a molecule used in transmission of nerve impuses
_____ factors appear to be much more important that genetic factors in ETTH
Environmental (fumes, mold, light, noise, etc.)
Migraine is a ______ disorder
neurogenic
In migraine a disorder of sensory processing produces what?
a pain matrix malfunction that amplifies nociceptive signals in the trigemino-thalamo-cortical pathway
List the 4 characteristics of migraine headaches, 2 of which someone must have in order to be diagnosed.
- Unilateral location
- Pulsating quality
- Severity interfering with daily activities
- Aggravation from routine physical activity
During a migraine headache, what other symptoms that a patient may experience?
- nausea, vomiting, photophobia, and photophobia
What are the 4 signs that a headache may be caused by excessive pressure, hydrocephalus, or tumor?
- Headache present at waking
- Pain triggered by coughing, sneezing, or straining
- Vomiting
- Symptoms worsen when lying down
What are the 4 signs that a headache is caused by serious intracranial disease, tumor, encephalitis, or meningitis?
- Progressive, worsening over days or weeks
- Neck stiffness, vomiting (irritation of meninges)
- Rash, fever (bacterial meningitis, Lyme disease)
- History of cancer, HIV, or infection
What are the 3 signs that a headache may be caused by hemorrhage?
- Headache after a head injury
- Abrupt onset
- Headache associated with onset of paralysis or reduced level of consciousness
What is whiplash?
an injury to the neck resulting from rapid acceleration or deceleration
What are the 2 syndromes that involve other systems in addition to the pain system?
- Complex regional pain syndrome
- Chronic low back pain syndrome
What does complex regional pain syndrome involve?
The somatosensory, autonomic, and motor systems
What are the symptoms of complex regional pain syndrome?
- intense pain in a limb
- swelling
- changes in skin color and temperature
- sweating
- atrophy
What does chronic low back pain syndrome involve?
muscle guarding, disuse, and abnormal movements
Although cutting selected dorsal roots or the spinothalamic tract should eliminate pain sensation, it often fails in practice, why?
The CNS changes in response to the original maintained pain or to pain-mediating fibers traveling in the dorsal columns
What 3 things affect the experience of pain?
- expectations
- cognition
- emotions
What does the amount of pain an individual expects influence?
Processing in both the medial and lateral pain systems
What are the 3 D’s of chronic pain?
Distress
Disuse
Disability
What types of psychological interventions may decrease activation of the pain system and also improve coping skills?
- Relaxation
- Biofeedback
- Cognitive behavioral therapy
- Imagery
What is placebo-associated improvement is defined as?
Any genuine psychological or physiologic effect that is attributable to receiving a substance or undergoing a procedure, but is not due to the inherent powers of that substance or procedure
What should therapeutic approaches that want to mobilize placebo-associated improvement include?
- positive (yet honest) communication about the therapy
- providing encouragement and education
- developing trust, compassion, and empathy
- understanding the person as an individual
- creating rituals that provide meaning and expectancy for the person
What is the most conflict between people with chronic pain and HCPs?
Most patients with pain fell misunderstood and stigmatized by health care professionals. They wanted HCPs to acknowledge their pain as biologically based, whereas HCPs are frequently more concerned with the diagnosis and treatment than with providing biological explanations for chronic pain.
