Lecture 18 chronic pain

Question 1

Describe chronic pain

Answer 1

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Question 2

Discuss the link between chronic pain and poor sleep and evidence regarding why this relationship may exist.

Answer 2

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Question 3

Describe Fibromyalgia

Answer 3

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Question 4

What is Chronic pain

Answer 4

Pain that outlasts the expected healing time (3-6mo).
Generally not due to residual injury/inflammation.
Poor correlation between signs of injury and pain
20-25% osteoarthritis patients who have knee/hip replacement don’t get improvement in pain.
10% -50% depending on type of pain.
Increased pain sensitivity a good indicator of future chronic pain.

Question 5

Predisposing factors to Chronic Pain

Answer 5

Women have 1.5-2x higher pain sensitivity and about double the rate of chronic pain.
Early life pain/stress and prior injury increase adult pain sensitivity/persistent pain.
Stress: rat pup separation from mum.
Psychological/Personality factors such as a fear of pain, catastrophising individuals etc.
Depression and Anxiety (reciprocal relationship)

Question 6

Chronic pain pathophysiology

Answer 6

Due to neuroplasticity both peripherally and centrally.
Peripheral changes in multiple receptors.
Pain neurons grow and increase synaptic connections to second order neurons in the medulla.
Glial cells in the spinal cord remodel to intensify pain transmission.
CNS changes resulting in central sensitisation.
Complex and incompletely understood but Pain becomes a disease in itself.

Question 7

Cost of Chronic Pain

Answer 7

The total economic cost of chronic pain in Australia in 2007 was estimated at $34 Billion ($11 Billion productivity costs, $7 Billion direct health care costs).
In USA: US$560–635 billion in 2010.

Question 8

Depression and Chronic Pain

Answer 8

~65% of patients presenting with depression have chronic pain.
50% of patients in pain clinics have depression.
Longitudinal studies have shown depressive symptoms predict future chronic pain.
Comorbid patients have more intense pain, greater disability from pain and poorer response to pain treatments/rehabilitation.
Treating the depression improves pain treatment

Question 9

Psychological interactions

Answer 9

Pain experience go either to no fear or catastrophizing and a vicious cycle - see slides for detail

Question 10

Meditation and Pain

Answer 10

Numerous studies shown pain is reduced following mindfulness meditation.
Following meditation:
Reduced pain related activation of the somatosensory cortex and insula
Increased (contrary to expectation) activation of anterior cingulate.
Reduced amygdala activation and negative emotions in response to pain.
Pain relief from meditation is not due to endorphins.

Question 11

Sleep and Pain

Answer 11

Chronic Pain: ~20% population.
Chronic Insomnia: ~10% of the population.
Pain and Insomnia Comorbid: 55-88%
Prospective studies show sleep disruption and insomnia in particular increase the risk of developing chronic pain.
Pain can inhibit sleep too.
Reciprocal relationship between sleep and pain.

Reduced SWS and REM cause hyperalgesia whereas warmth detection and other tactile stimuli are unchanged.
4 possible mechanisms
Descending pain inhibitory pathway
Inflammation
Attentional regulation
Central sensitisation

Question 12

Descending pain inhibitory pathway

Answer 12

Assess through conditioned pain modulation:

Increased pain threshold to a secondary stimulus
Due to release of endogenous opioids in PAG.

Question 13

Descending pain inhibitory pathway - icewater chalalnge, what the experiment was about and what was the findings

Answer 13

3 day of restricted sleep reduced conditioned pain modulation, surprisingly the bigegst reduction was not on the night of total sleep dep but the second night of partial sleep dep

Question 14

Attentional regulation

Answer 14

Sleep loss impairs neurocognitive function, maybe distraction is poor when tired.
28 Healthy subjects who naturally slept >6.5 hrs and <6.5 hrs/night were studied.
Pain alone (Capsaicin + hot probe)
Video game plus pain
Measured pain as well as redness (inflammation) and area of sensation alteration (central sensitisation)

Question 15

Sleep alters attentional regulation of pain

Answer 15

Distraction reduced pain rating in well slept individuals, but had no impact on individuals who sleep less than 6.5 h.
Also more redness and larger zone of altered sensation in low sleep group indicating inflammatory and spinal modifications.

Question 16

Summary: sleep loss → Pain

Answer 16

Sleep loss may increase pain by:
Reducing descending pain inhibition
Increasing inflammatory cytokines
Reducing inhibition from distraction
Modified central pain sensitisation

Question 17

Fibromyalgia

Answer 17

SYMPTOMS
Chronic widespread pain, with some of:
Unrefreshing sleep (90%), fatigue (70%)
Cognitive impairment, lifetime depression
GI symptoms
Allodynia (non pain 
stimulus becoming 
Painful)
2% prevalence

Central processing of pain altered.
Lower pressure pain threshold
Increased somatosensory activation for any level of pressure.
Ascending pathways abnormal.
Increased CSF Substance P and Nerve Growth Factor.
Descending pathways may be abnormal too
Increased CSF serotonin and norepinepherine
Reduced rostral anterior cingulate activity

Question 18

Sleep in Fibromyalgia

Answer 18

Complaints: No Insomnia but restless and or light sleep with frequent awakening.
Poor sleep associated with worsening of symptoms.
PSG show: Reduced SWS and spindles in N2 along with alpha intrusion.

Question 19

What is peculiar about the sleep of people with fibromyalgia

Answer 19

alpha-delta sleep

intrusion of alpha into dealta wave akin to those induced by alcohol

Question 20

Correlation or causation?

Answer 20

Study of >12k Norwegian women without musculoskeletal disorder followed up over 10yr.
Poor sleep quality predicted Fibromyalgia development.
Similar UK study showed non-restorative sleep strongest predictor of widespread pain

If you improve sleep does it improve fibromyalgia?
Sodium oxybate (GHB):
Yes for pain, sleep, fatigue and quality of life.
CBTI:
yes for sleep, fatigue and daily functioning, pain catastrophising
no for pain…

Question 21

Preventing Chronic Pain

Answer 21

Studies show best way to reduce chronic pain is to reduce acute pain (morphine before surgery reduces the incidence of chronic pain).
Prevention better than cure!
Can’t always prevent pain, but…
Get good sleep.