Acute and Chronic Pain Flashcards
What are the different ways to classify pain?
- Length (Acute/Chronic)
- Physiology (Nocicpetic/Neuropathic)
- Etiology
- Affected Area
What is acute pain primarily due to?
Nociception
What is chronic pain primarily due to?
- Neuropathic
- Physiological and behavior factors
What are the four major processes of pain?
- Transduction
- Transmission
- Modulation
- Perception
What is transduction?
- Noxious stimuli are converted to nerve impulses by nociceptors.
Fibers that transmit “fast pain” that is sharp and well localized.
A-δ fibers
Fibers that transmit “slow pain” that is dull and poorly localized.
C fibers
How will inflammation contribute to the threshold of pain stimulus?
Reduce threshold to pain stimulus (allodynia)
How will inflammation contribute to the response to pain stimulus?
Increase response to pain stimulus (hyperalgesia)
What are the inflammatory mediators involved in Transduction?
- Prostaglandin
- Bradykinin
What are the excitatory mediators involved in Transduction?
- Glutamate
- CGRP
- NGF
- SP
What are the inhibitory mediators involved in Transduction?
- Opioids
- SST
- Cannabinoids
What is transmission?
Pain signals are relayed from the afferent pathway along the spinothalamic tract to the brain.
What is the first-order neuron?
- Pain signal from periphery to dorsal horn (cell body in dorsal root ganglion)
- Pain source to spine
What is the second-order neuron?
- Signal from dorsal horn to thalamus (cell body in dorsal horn)
- Spine to brain
What is the third-order neuron?
- Thalamus to the cerebral cortex (cell body in the thalamus)
- Brain to cerebral cortex
What is Modulation?
The process where the pain signal is amplified or dampened as it advances toward the cerebral cortex.
What is the most important site of modulation?
Substantia Gelatinosa in the Dorsal Horn (Lamina II and Lamina III)
Where does the descending inhibitory pathway begin before it is projected to the Substantial Gelatinosa?
- Periaqueductal Gray
- Rostroventral Medulla
How is pain inhibited?
- Spinal neurons release GABA and glycine (inhibitory NT)
- Descending pathway release NE, 5HT, and endorphins
How is pain augmented?
- Central sensitization
- Wind-up
Where does modulation occur?
- Nociceptor in the spinal cord
- Nociceptor in the supraspinal structures
How is peripheral modulation of pain facilitated?
Nociceptors and neurons display sensitization from repeated stimulation
How is peripheral modulation of pain inhibited?
Peripheral exogenous opioid release
How is central modulation of pain facilitated?
- Wind-up and sensitization of second-order neurons
- Receptive field expansion
- Hyperexcitability of flexion reflexes
How is central modulation of pain inhibited?
- Segmental inhibition (signal stops in second-order neuron and spinothalamic tract)
- Supraspinal inhibition (signal sent down the spinal cord to inhibit pain at the dorsal horn)
What is perception?
How we process afferent pain signals in the cerebral cortex and limbic system
What drugs can prevent pain Transduction?
- NSAIDs
- Antihistamine
- Opioids
- LA
What drugs can prevent pain Transmission?
- LA
- Opioids
What drugs can prevent pain Modulation?
- Opioids
- Alpha-2 agonist
- NMDA receptor antagonists
What drugs can prevent pain Perception?
- Opioids
- Alpha-2 agonist
- General Anesthesia
What are the two types of Neuropathic Pain?
- Central
- Peripheral
What are the two types of Nociceptive Pain?
- Visceral
- Somatic
What are the two types of Visceral Pain?
- True
- Parietal
What are the two types of Somatic Pain?
- Superficial
- Deep
What is the most common cause of acute pain?
Nociceptive Pain
What is the benefit of having acute pain?
Serves to detect, localize, and limit tissue damage (ie: hot stove)
How is somatic superficial pain characterized?
- Well localized
- Sharp
- Pricking, Throbbing, Burning
How is somatic deep pain characterized?
- Less well-localized
- Dull, aching
What is the cause of visceral pain?
D/t disease process or abnormal organ function
How is true visceral pain characterized?
- Can be localized or referred
- Dull, diffused, usually midline
How is parietal visceral pain characterized?
- Can be localized or referred
- Sharp, stabbing localized to the organ or distant site
How is chronic pain categorized?
- Malignant (R/t CA and its treatment)
- Nonmalignant (Neuropathic, musculoskeletal, inflammatory)
What are the different types of Chronic Pain Syndromes?
- Somatic (low back pain, degen. disc sx, failed back sx.)
- Visceral (abdominal CA, pancreatitis)
- Neuropathic (CRPS, trigem. neuralgia, phantom pain)
This type of pain is caused by injury to the Nervous System.
Neuropathic Pain
- Result of tumor compressing nerve or spinal cord
- Cancer actually infiltrating into nerves or spinal cord
- Diabetic neuropathy
How is chronic pain developed?
- Peripheral sensitization: Injury → chemical release → sensitizing area. ↓ Threshold and ↑ response to nociception.
- Central sensitization: Membrane excitability, synaptic recruitment, and ↓ inhibition. Uncoupling of pain from peripheral stimuli.
What is sensitization?
The process where repeated stimuli reduce the threshold of primary afferent nociceptors.
What is Complex Regional Pain Syndrome (CRPS)
Neuropathic pain disorder (chronic pain condition) usually affecting a limb after an injury or surgery,
What are the risk factors to developing CRPS?
- Previous trauma or surgery
- Nerve injury (Causalgia, Type II)
- Work-related injury
- Female
What are the two types of CRPS?
- Reflex sympathetic dystrophy (Type I)
- Causalgia (Type II) - documentation of a prior nerve injury
Signs and Symptoms of CRPS?
- Spontaneous pain
- Hyperalgesia
- Allodynia
- Active and passive movement disorders
What is Reflex sympathetic dystrophy (Type I)?
- Pain disproportionate to injury.
- Pain persists beyond the time the tissue-damaging process has ended.
How does the sympathetic nervous system play a major role in Reflex Sympathetic Dystrophy?
Sympathetic outflow can induce the discharge of primary afferent nociceptors
Selective blockade of the sympathetic outflow provides relief.
What will continuous sympathetic outflow cause to the muscle?
Nociceptor activity will cause muscle contractions (sometimes sustained)
Use of Skeletal Muscle Relaxants will provide relief
What is Causalgia (Type II)?
Causalgia arises after an injury or trauma to a peripheral nerve.
The most common site of CRPS II pain is the ____________.
Brachial Plexus
Where is CRPS Type II pain generally localized?
Around the injured nerve
What are the symptoms of Type II pain?
- Similar to Type I (burning, aching)
- Pain exceeds 6 months
Complex Post Surgical Pain (CPSP) affects what percentage of patients?
10%
- Begins as “difficult to control” acute postoperative pain
- Becomes persistent pain with neuropathic features and unresponsive to opioids
What is considered Complex Post Surgical Pain (CPSP)?
- Pain that persists longer than expected
- 3-6 months post-op
- D/t possible nerve damage during the procedure
Described as hyperalgesia, dysaesthesia, allodynia
What is the first-line treatment for neuropathic pain?
- TCA
- SNRI
- Gabapentanoids
- Topicals
4-6 week time line for drugs to reach therapeutic levels and assess effectiveness.
What is the third-line treatment for neuropathic pain?
- Referred to Pain Specialist
- SSRIs/ Anticonvulsants/ NMDA Antagonist
- Interventional Therapies
What is the fourth-line treatment for neuropathic pain?
Neuromodulation (Stimulator Trial)
Will need >50% pain relief w/ trial before implant
What is the fifth-line treatment for neuropathic pain?
Low Dose Opioids
4-6 week time line for drugs to reach therapeutic levels and assess effectiveness.
What is the sixth-line treatment for neuropathic pain?
Targeted Drug Therapy (Implantable Pain Pump Trial)
Will need >50% pain relief w/ trial before implant
When will Interdisciplinary Management of Chronic Pain be the most helpful?
Helpful in Chronic Non-malignant Pain
Psychologist, PT, OT, Anesthesia combo
What is the most studied antidepressant for tx of neuropathic pain?
- Tricyclic Antidepressant (TCA)
- First-line treatment of neuropathic pain
MOA of TCA
- Inhibition of serotonin and norepinephrine re-uptake
- Blocks histamine, adrenaline, ACh, and Na Channels
- Pain relief at 20-30% of effective antidepressant dose
What are the most commonly studied SNRIs for tx of neuropathic pain?
- Duloxetine (Cymbalta)
- Venlafaxine (Effexor)
MOA of SNRIs
Facilitate descending inhibition by blocking serotonin and noradrenaline (NE) reuptake.
SNRIs will be most helpful in these patients dealing with neuropathic pain.
- Peripheral diabetic neuropathy
- Peripheral neuropathy
- Osteoarthritis
- Chronic low back pain
- Fibromyalgia
- Depression
What anticonvulsant drugs are most commonly used to treat neuropathic pain?
- Gabapentin (Gralise, Neurotin, Horizant)
- Pregabalin (Lyrica)
- Carbamazepine
Dose of Gabapentin.
MAX dose.
- 600 mg TID
- MAX daily dose: 3600 mg
Dose of Pregabalin.
MAX dose.
- 150 mg BID or TID
- MAX daily dose: 600 mg
When will lidocaine patches be ineffective?
- Post-surgical neuropathic pain
- Diabetic neuropathy w/ allodynia or hyperalgesia
MOA of Topical Capsaicin
- Binds to TRPV1 receptor located on Aδ and C-nerve fibers
- Release Sub-P and depolarize the nerve
- Long term exposure → overstimulation, ↓ Sub-P = Desensitization of nerve and reversible nerve degeneration
What concentration of Topical Capsaicin is recommended for neuropathic pain?
8%
MOA of Tramadol
- Weak mu-opioid agonist
- Inhibitor of serotonin and NE reuptake
Effective in Tx of Neuropathy in Diabetics, postherpetic, and CA related pain
What are possible procedural therapies for neuropathic pain?
- Somatic blocks (Trigeminal nerve block)
- Sympathetic blocks (Celiac plexus block)
- Epidurals/ Radiofrequency ablation
- Implantable stimulators (Spinal orDeep Brain)
MOA of Ketamine
- NMDA Antagonist
- Astrocyte activation may stop the progression of neuropathic pain at its source
Cells involved in neuralgia at the central level
- Ependymal cells
- Oligodendrocytes
- Astrocytes
- Microglia
Cells involved in neuralgia at the peripheral level
- Satellite cells
- Schwann cells
What is the hallmark sign of neuropathic pain?
- Elevated extracellular levels of glutamate
- This results in the presynaptic release of more glutamate
- Impairs glutamate reuptake from glial cells
- Increase pain sensation and transmission
What β-lactam can be used to treat neuropathic pain?
Ceftriaxone
What β-lactamase inhibitor can be used to treat neuropathic pain?
Clavulanic Acid
What is Targeted Drug Delivery?
- Delivery of medication to the site of action at the dorsal horn
- Increases potency of medication
What does Targeted Drug Delivery bypass?
- First-pass metabolism
- Blood-brain barrier
What medications are usually used in Targeted Drug Delivery?
- Morphine
- Ziconotide (N-type calcium channel blocker)
Benefits of Physical Activity for Pain
- 30% improvement in low back pain
- Extremely effective for centralized pain conditions
- Cheap
What supplements can be used to aid sleep?
- Melatonin 3-10 mg qHS
- L-theanine 200 mg qHS
- Magnesium 200-600 mg (titrate to SE of loose stools)
What medications can be used to aid sleep?
- Cyclobenzaprine 5-10 mg (2 hr before bed)
- Amitriptyline 25-50 mg qHS
- Duloxetine 30-60 mg qHS
- Gabapentin 300-600 mg qHS
What lab is an accepted marker of chronic inflammation?
- CRP
- Obese patients are prone to chronic non-resolving inflammation
- Elevated CRP → increase rates of low back pain
What diets can decrease inflammation?
- Fruits
- Vegetables
- Omega 3 Fatty Acids
What diets are anti-inflammatory?
- Fruits
- Vegetables
- Legumes
- Healthy oils/ Omega
What items are involved in the Mediterranean diet?
- Vegetables
- Fish
- Olive oil as main fat
What are the two non-essential amino acids?
- Glutamate
- Asparate
- Both act as excitatory NT
What is the most common negative emotion with chronic pain?
Anxiety
Education surrounding the cause of pain found to reduce pain in patients with fibromyalgia
What is Tension Myositis Syndrome
A condition characterized by chronic muscle pain d/t psychological stress, emotional triggers, and tension rather than physical injury.
Integrated Chronic Pain Management
Integrated Chronic Pain Management
What is the second-line treatment for neuropathic pain?
- Tramadol
- Combo 1st line therapies
4-6 week time line for drugs to reach therapeutic levels and assess effectiveness.
