Lecture 19 - Chronic Pain

Question 1

What is the definition of chronic pain?

Answer 1

Pain that outlasts the expected healing time (generally over 3 months).

Question 2

In general, is chronic pain due to residual injury or inflammation?

Answer 2

No.
There is a poor correlation between signs of injury and pain in those with chronic pain.

Question 3

Is it true that 20-25% of osteoarthritis patients who have a hip/knee replacement continue to have chronic pain?

Answer 3

Yes. Indicating that chronic pain is not just due to injury.

Question 4

What types of chronic pain are there?

Answer 4

Nociceptive/inflammatory pain.

Neuropathic pain.

Dysfunctional pain.

Question 5

Why do those who experience chronic pain become more sensitised to pain?

Answer 5

Repeated activation increases nociceptor sensitivity to pain (hyperalgesia).
This is peripheral sensitization.

Question 6

What is centralised sensitization?

Answer 6

Persistent signals from the peripheral nervous system can also sensitise pain signals in the CNS, such as an increased sensitivity of second-order neurons involved in pain signals.

Question 7

In healthy individuals, how does the body respond to prolonged pain?

Answer 7

Pain is our body’s alarm system to signal to the body that we are in danger of tissue damage or our survival is being threatened (as in emotional pain). Prolonging the pain is unnecessary and potentially inhibiting and so once pain has been going for a bit our brain releases endorphins, which bind to opioid receptors in the PAG area, in turn sending down-stream signals to the peripheral nervous system to dampen response from nociceptors.

Question 8

How does pain sensitivity increase in those with chronic pain?

Answer 8

The nociceptor become more easily activated. Their threshold for activation decreases.
Synaptic connections to second-order neurons in the medulla also increase, increasing their sensitivity to pain.
Descending pain modulation pathways also alter, such that they do not dampen pain as much, and/or increase signal of pain from nociceptors.

Question 9

What are some of the risk factors that increase risk of chronic pain?

Answer 9

Nerve damage during surgery.
Open surgery, as opposed to laproscopy.
Surgery lasting over 3 hours.
Being a woman.
Mood disorders.

Question 10

What is opioid-induced hyperalgesia?

Answer 10

Increased pain sensitivity due to prolonged or excessive/high-dose use of opioids.

Question 11

What are some of the factors that predict lower levels of pain in those suffering with chronic pain?

Answer 11

Good social relationships.
Good psychological wellbeing.
Pain acceptance.

Question 12

What are some of the factors that predict higher levels of pain in those with chronic pain?

Answer 12

Anxiety.
Catastrophising.

Question 13

Being a woman is a risk factor of developing chronic pain.
What is the difference in rates of chronic pain between women and men?

Answer 13

Women experience chronic pain at twice the rate of men.

Question 14

Do prior injuries increase risk of developing chronic pain?

Answer 14

Yes.

Question 15

Does our perception of pain involve only the processes involved in nociception?

Answer 15

No. Many other areas of the brain are activated in response to pain beyond those involved in the sensory perception of pain.

Question 16

Are the areas of the brain involved in the ascending pathway of pain signals, such as the thalamus, the areas that become dysfunctional in chronic pain?

Answer 16

No.
It is the areas involved in the descending pathway, such as the dlPFC and PAG, as well as the emotional/reward areas, such as the hippocampus, that become dysregulated or dysfunctional in chronic pain.

Question 17

When we look at MRIs of healthy patients and those with chronic pain, what can be seen in regards to their ‘pain profiles’ in response to spontaneous pain or the ‘pain profile’ for those with chronic pain?

Answer 17

The pain profiles for spontaneous and chronic pain are different. Different areas of the brain are activated, suggesting that the experience of chronic pain is differentiated from spontaneous pain. There is something more going on than what is experienced in spontaneous, finite pain.

Question 18

Do those who have recovered from chronic pain show the same pain signature as those who continue to have chronic pain?

Answer 18

No.
The pain signature seen in the brain goes away for those who have recovered from chronic pain.

Question 19

Has the nucleus accumbens been found to have decreased volume in those with sub-acute and acute chronic pain?

Answer 19

Yes.

Question 20

What percentage of those with depression also have chronic pain?

Answer 20

About 65%

Question 21

What percentage of those who present to pain clinics also have depression?

Answer 21

About 50%

Question 22

Do depressive symptoms predict future chronic pain?

Answer 22

Yes.

Question 23

It has been found that those with depression have more tolerance (lower sensitivity) to certain noxious stimuli than non-depressed individuals, whereas they have lower tolerance (more sensitivity) to other noxious stimuli.

Which stimuli do those with depression have higher tolerance for?
Which do they have lower tolerance for?

Answer 23

Those with depression appear to have more pain tolerance for thermal and electrical pain.

Those with depression appear to have lower pain tolerance for pressure pain.

Question 24

Is the DLPFC involved in depression?

Answer 24

Yes.
This could be one of the areas that give rise to the link/association between chronic pain and depression.