Neuropathic pain

PH3113 Unit

What is neuropathic pain?

Abnormal pain signalling that responds poorly to normal analgesics

How is neuropathic pain different to nociceptive pain?

Caused by nervous system dysfunction rather than tissue injury

What are the common examples of neuropathic pain?

Chronic back pain

Nerve entrapment

Post traumatic pain

Neuralgia

Post herpetic neuralgia

Cancer related neuropathic pain

Causalgia

what is trigeminal neuralgia?

Severe facial pain caused by abnormal firing of trigeminal nerve

What is central sensitisation?

Hyperresponsiveness of dorsal horn neurones after repeated nociceptor activation

Why are opioids less effective in neuropathic pain?

Do not easily reverse the sensitisation changes caused by hyperresponsiveness

What is the function of the periaqueductal grey (PAG)?

Integrates signals from high centres and modulates pain transmission

What neurotransmitters are involved in the descending pathway?

serotonin and noradrenaline

How does the descending pathway reduce pain?

Inhibit ascending pain transmission in the dorsal horn

How do antidepressants help neuropathic pain?

By increasing serotonin and noradrenaline in descending inhibitory pathways that inhibit ascending pathways

What antidepressant classes are used in neuropathic pain?

TCAs and SNRIs

What is nefopam?

Non opioid analgesic

What neurotransmitters does nefopam affect?

Serotonin, dopamine, NA

What is the opioid sparing effect of nefopam?

Reduces opioid dose needed for analgesia

What additional benefit does nefopam have after surgery?

Prevents shivering

Why is serotonin described as bidirectional in pain?

Because it can inhibit or facilitate pain depending on pathway and receptor subtype

What is the role of serotonin in the descending pathway?

Suppresses ascending pathway transmission

Which brainstem structure is linked to serotonergic descending pathways?

Nucleus raphe magnus

Which serotonergic receptor is linked to analgesic actions?

5HT3

Which serotonergic receptor is involved in opioid analgesia?

5HT7

What two mechanisms contribute to tramadol’s analgesic effect?

Weak opioid activity and serotonin/ NA reuptake inhibition

What is Tramacet?

Combination of paracetamol and tramadol

What is multimodal analgesia?

Combining drugs with different mechanisms to improve pain relief

What property of Tramadol’s formulation means it has two MOA?

Racemic mixture

What opioid receptors does Tramadol act on?

All

Why is tramadol a danger in epilepsy?

Lowers seizure threshold

What are the common opioid side effects of Tramadol?

Nausea, dizziness, constipation and drowsiness

What antidepressants act dangerously with Tramadol?

SSRI, SNRI, TCAs MAOIs

What are the two broad categories of neuropathic pain?

Central and peripheral neuropathic pain

What are the NICE first line drugs for neuropathic pain?

Amitriptyline, Duloxetine, Pregabalin and Gabapentin

What drug is commonly used for post herpetic neuralgia?

Gabapentin

What conditions is pregabalin licensed for?

Diabetic neuropathy and fibromyalgia

What is the first line treatment for trigeminal neuralgia?

Carbamazepine

What receptors do cannabinoids act on?

CB1 and CB2

What effects will CB1 reduce?

Hyperalgesia and Allodynia