Pain Pathophys and Pharm

Question 1

What is the definition of Nociception?

Answer 1

Sensory detection of tissue damage or stimuli that can potentially damage tissue

Question 2

What are the 3 Nociceptor Afferent Fibers? Describe each.

Answer 2

• C fibers:
  
  • respond to thermal, mechanical, and chemical = polymodal; dull pain
  • smallest unmyelinated, transmit at slowest speed
• A-delta:
  
  • respond to intense mechanical and thermal, first sharp pain
  • thinkly myelinated, transmit at fastest
• A-beta:
  
  • respond maximally to light touch and may modulate pain

Question 3

Pain modulation by Periaqueductal Gray (PAG) is stimulated by input from what 3 sources?

Answer 3

1) thalamus
2) hypothalamus
3) amygdala

Question 4

What 2 sites does the Periaqueductal Gray activate? What do these do activated sites do?

Answer 4

Raphe nuclei:

• sends inhibitory enkephalinergic and serotonergic axons to dorsal horn (via dosrolateral funiculus) to inhibit pain transmission

Locus coeruleus:

• sends separate noradrenergic inhibitory axons

Question 5

What usually causes visceral pain? How is it often described?

Answer 5

Usually caused by stretching of unmyelinated fibers that innervate the walls of organs

“crampy, dull or achy”

Question 6

Where is visceral pain usually felt? Why is it poorly localized?

Answer 6

Intraperitoneal organs are bilaterally innervated, so visceral pain is independent of right or left anatomic origin.

Question 7

What is parietal (somatic) pain?

Answer 7

Inflammation of parietal peritoneium; localized to dermatone superficial to the site of the painful stimulus

Question 8

What is the definition of referred pain?

Answer 8

Pain localized in part of body that is remote from its source

Question 9

What is the mechanism of referred pain?

Answer 9

Visceral afferent nerve fibers enter the spinal cord very close to input from sensory nerve fibers from skin or underlying muscle. Since there are more sensory nerve fibers and they are more strongly stimulated, the pain is perceived as coming from the skin or muscle.

Question 10

3 common examples of referred pain (location and pain location)

Answer 10

location, pain location:

diaphragm, shoulder (but when you press on shoulder, you feel no pain)

heart, precordium and inner side of arm

ureter, testis

Question 11

endogenous opioid peptides and their preferred receptor

• B endorphin
• Enkephalin
• Dynorphin

Answer 11

• B endorphin: mu
• Enkephalin: delta
• Dynorphin: **kappa **

Question 12

opiates effect on decreasing pain [1(3), 1]

Answer 12

• inhibits ascending pathways of pain
  
  • inhibits the presynaptic release and postsynaptic response to excitatory neurotransmitters (e.g. substance P)
  • inhibits spinal cord transmission neurons
  • inhibits activity in the thalamus
• activate descending inhibitory pathways

Question 13

Toxicity of NSAIDs (4 areas)

Answer 13

KIDNEY:

• decreased kidney function in patients with decreased ECV or underlying kidney disease
• NA retention (prostaglandins natriuretic)

HEART:

• increased BP (average 5 mmHg) // Hypertension

PLATELET:

• nonselective reversible effect (COX2 no effect)

GI:

• ulceration (less with COX2)
• dyspepsia without ulceration

Question 14

Opioids cause constipation which does not go away while on drug. What is the mechanisms?

Answer 14

mechanism: CNS effect, but mainly due to binding to mu2 opioid receptors in intestine

Question 15

what is the treatment for constipation as a side effect of opioids? (3)

Answer 15

• prophylaxis with stimulant laxative (Senna) - do NOT wait for them to get constipated. start right away
• injectable methylnaltrexone for severe constipation
• oral alvimopan (mu antagonist)

Question 16

Uses for SNRI (2 drugs) as adjuvant analgesis

Answer 16

Duloxetine:

• post herpetic neuralgia
• diabetic neuropathy
• fibromyalgia

Venlafaxine:

• post herpetic neuralgia
• diabetic neuropathy

*recall that SNRIs block serotonin and NE reuptake*

Question 17

Side effects of low dose tricyclics

Answer 17

used for any persistent pain, especially neuropathic

Amitriptyline

• Antihistamine: tired AF
• Anticholinergic: dry mouth, urinary retention, constipation
• Alpha blocker: orthostatic hypotension

Despiramine and Nortriptyline - less of these effects

Question 18

Description of neuropathic pain

Answer 18

burning, shooting, stabbing paresthesias

Question 19

definition of allodynia

definition of paresthesia

Answer 19

allodynia: pain resulting in a stimulus (such as light touch) that does not normally elicit pain
paresthesia: spontaneous intermittent painless abnormal sensation

Question 20

what are the symptoms of painful diabetic neuropathy?

Answer 20

paresthesias (tingling uncomfortable feeling)

allodynia

hyperalgesia

Question 21

Treatment for painful Diabetic Neuropathy (legs first i.e. longer axons) (6)

Answer 21

• Notriptyline or Desipramine (low dose TCA) - many feel drug of choice
• Duloxetine or Venlaxafine (SNRI)
• Gabapentin/Pregabalin (anticonvulsants)
• Topical lidocaine
• Tramadol (mild mu agonist, mild SNRI, not a first line drug)
• Oxycodone (opioids not 1st line)

often need mroe than one med

Question 22

symptoms of post-herpetic neuralgia

Answer 22

steady burning pain

electric shock

allodynia

Question 23

treatment for Post Herpetic Neuralgia (4)

Answer 23

1) antivirals within first 72 hours may decrease acute pain but not PHN
2) Gabapentin or Pregabalin (initial therapy)
3) Tricyclics or desipramine (if not depressed)
4) Lidocaine patch (some benefit from this)

VACCINATE patients older or equal to 60 years