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Flashcards in Pain Mechanisms Deck (22)
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1
Q

What is hyoeralgesia?

A

Increased pain at a normal threshold resulting from peripheral or central sensitisation

2
Q

What is allodynia?

A

Pain from stimuli which are not normally painful or pain which occurs in an area not stimulated

3
Q

Give an example of allodynia

A

Arthritis in the knee - receptive field for pain is expanded to the thigh so that if the thigh is touched, causes pain

4
Q

How do hyperalgesia and allodynia occur?

A

Process of wind-up

  • occurs in persistent activation of pain afferents
  • get persistent activation and resultant upregulation of NMDA receptors
  • get increased glutamate release
  • causes excessive second order neurone firing
  • results in nociceptive fibres becoming hyper excitable
5
Q

What are the classifications of chronic pain?

A

Nociceptive pain
Neuropathic pain
Mixed

6
Q

What happens in chronic nociceptive pain?

A

Activation of nociceptors stimulating nociceptive signalling along Aδ and C fibres

7
Q

How is chronic nociceptive pain commonly described?

A

A sharp, stabbing pain

8
Q

What is an example of chronic nociceptive pain?

A

Arthritis
Long term activation of those fibres will result in wind-up, so many patients will eventually complain of hyperalgesia and allodynia

9
Q

What happens in chronic neuropathic pain?

A

Pain of a neuronal origin
No classic stimulation of nociceptors, therefore difficult to treat
No single disease process

10
Q

What can cause neuropathic pain?

A

Diabetic neuropathies
Cancer compressing nerves
Trigeminal neuralgia

11
Q

Where does neuropathic pain commonly occur?

A

Brain
Spinal cord
Peripheral nerves

12
Q

How is neuropathic pain commonly described?

A

Burning
Tingling
Shooting

Hyperalgesia and allodynia common

13
Q

What are the two main mechanism of neuropathic pain?

A

Ectopic activity - upregulation of VG Na channels distal to damage, causing increased excitability of the nerve and ectopic action potentials to occur along the pain fibre

Ephatic activity - ectopic beats cause action potentials to be sent to activate adjacent nerve fibre bundles, causing receptor field expansion

14
Q

What is phantom limb pain and how does it develop?

A

The painful neuropathy resulting from neuroplastic changes in the CNS

15
Q

What happens in complex regional pain syndrome?

A

An injury initiates a pain impulse carried by sensory nerves to the CNS

The pain impulse triggers and impulse in the SNS which returns to the original site of injury

This triggers an inflammatory response causing the vessels to spasm, swelling and increased pain

Pain triggers another response, establishing a cycle of pain and swelling

Results in burning extremity pain and oedema

16
Q

Mechanism of action of opiates to reduce pain?

A

Bind to MOP/KOP/DOP which are GPCRs
Close VG Ca channels
Open K+ channels to hyperpolarise the membrane and inhibit cAMP formation

Overall, this inhibits neurotransmitter release

17
Q

ADRs of opiates?

A
Respiratory depression
Nausea and vomiting 
Antitussive 
Constipation 
Itching 
Euphoria
18
Q

Which endogenously-released opiates act on which receptors?

A

Endorphins - MOP

Enkephalins - DOP

Dynorphins - KOP

19
Q

What are the different steps in the management of pain?

A

Step 1: non-opioid use

Step 2: incorporate weak opioids

Step 3: strong opioids

20
Q

What type of pain are opioids bad at managing?

A

Neuropathic pain - eg in nerve compression or destruction, will respond poorly

21
Q

What are some adjuvant analgesics that can be used with opioids?

A
NSAIDs
Paracetamol
Local anaesthetics
Cannabinoids
Capsaicin
Ketamine
Tricyclics
Anticonvulsants
22
Q

What is chronic pain?

A

Pain or discomfort persisting continuously or intermittently for greater than 6 months