Neuropathic Pain Flashcards
What causes neuropathic pain?
Pain initiated or caused by a primary lesion or disease of the somatosensory system
What are the types of neuropathic pain?
Peripheral neuropathic pain (Pain initiated or caused by primary lesion or disease in peripheral somatosensory system) Central neuropathic pain (Pain initiated or caused by a primary lesion or disease in the central somatosensory system)
What causes peripheral neuropathies most commonly?
Metabolic conditions such as diabetes Toxic conditions: Alcohol, chemotherapy, etc Postinfectious (PostHepaticNeuralgia, HIV, CMV)
What are the 3 most common causes of central neuropathic pain?
Spinal cord injury Post-stroke pain Multiple sclerosis
What causes postraumatic neuropathic pain?
Sciatica Postoperative pain Neuroma/nerve entrapment Phantom limb pain Complex Regional Pain Syndrome (CRPS)
How common is neuropathic pain?
20 - 24% of diabetics = peripheral neuropathy 25 - 50% of patients >50 with herpes zoster develop PostHepaticNeuralgia Up to 20% develop post mastectomy pain 1/3rd of cancer patients have neuropathic pain >50% of low back pain patients have associated neuropathic pain
What are the physiological mechanisms of peripheral neuropathic pain?
Membrane hyperexcitability (ectopic discharges) Peripheral sensitisation
What are the physiological mechanisms of central neuropathic pain?
Membrane hyperexcitability Wind up Central sensitisation Denervation supersensitivity Loss of inhibitory controls
How do peripheral pain receptors become hyperexcitable?
Damage to nerves results in overexpression of adrenoreceptors and sodium channels resulting in faster and more frequent action potentials
How is central neuropathic pain controlled?
Upregulation of calcium channels. Block is possible by opioid receptors and noradrenaline/serotonin receptors
What is homosynaptic sensitization What is the result? What is heterosynaptic sensitization what is the result?
Increased feeling of pain from touch due to convergence with a hyperalgesic interneuron that is also connected to a nociceptor. (hyperalgesia is the result) This is as opposed to allodynia seen in heterosynaptic sensitization where normal touch triggers a pain response.
What do glia do to create neuropathic pain?
They produce chemokines and cytokines which desensitize C-fibers to pain
What are the symptoms of CRPS?
Hyperalgesia and allodynia
How is neuropathic pain diagnosed?
LOOK LISTEN LOCATE Listen to patient history Look for sensory discrepancy. Locate (Think about if pain is neuroanatomically plausable.)
What kind of pain is neuropathic pain?
Pins and needles, shock - like, and burning
What are the positive and negative signs and symptoms of neuropathic pain?
Positive: Dysesthesias Paresthesias Spontaneous pain Stimulus-evoked pain Negative: Loss/impairment of sensory quality Numbness and reduced sensation
Conclusions neuropathic pain:
Result of lesion or disease of somatosensory system Very common but underdiagnosed and undertreated Diagnosed by Look Listen Locate Common presentation consists of positive and negative signs Range of validated tools help with diagnosis Neuropathic pain is terrible for quality of life.
What approaches are taken to manage neuropathic pain?
Pharmacotherapy Neurostimulatory therapy Interventional regional anaesthesia Lifestyle Psychological Physical rehabilitation
What concepts must be understood for treating neuropathic pain?
“dampen down” peripheral sensitization in damaged axon (sodium channel blockade) “dampen down” central sensitization (NMDA agonists and calcium channel blockers) “enhancing” descending inhibitory pathways (tricyclics/SNRIs, tramadol)
Read paper in literature called:
Pharmacotherapy for neuropathic pain in adults: a systematic review and meta-analysis Results show tricyclic antidepressants, serotonin-noradrenaline reuptake inhibitors (SNRIs), pregabalin, and gabapentin are great for first-line therapy for neuropathic pain.
What are the issues with taking antidepressants as analgesics?
Low doses increase compliance Often lots of adverse effects Effect needs time
What SNRIs are used for neuropathic pain?
Venlafaxine or duloxetine (more data on duloxetine)
Which drug types are being investigated for neuropathic pain?
Antidepressants (TCAs, SNRIs) Anticonvulsants (particularly the ones bound to α2-δ subunit of voltage gated calcium channels eg pregabalin) Opioids such as tramadol and tapentadol Lidocaine plaster
Which antidepressants have been shown to help with neuropathic pain?
TCAs and SNRIs
What does pregablin do to hyperexcited neuron?
It inhibits the calcium channel’s hyperexcitability
What is the NNT for pregabalin?
7.7
What does NNT mean?
Number needed to treat before 1 person experiences more than 50% pain relief. Low number is a good drug and high number is bad. This is compared to placebo. and does not mean only every 7th patient.
Does pregabalin help neuropathic pain patients sleep?
Yes, in fact it does not suppress REM sleep like many other drugs.
Do other anticonvulsants besides pregabalin work for neuropathic pain?
No evidence that they do and they are very dangerous. Carbamazepine is only proven to be effective in trigeminal neuralgia and facial pain.
Is carbamazepine effective in treating neuropathic pain?
Only in the case of trigeminal neuralgia and facial pain. Carbamazepine has lots of side effects though so it is better to use pregabalin.
Are opioids effective in treating neuropathic pain?
Yes, however not always and no necessarily completely.
What is the NNT50 of opioids?
4.3
What are the most effective opioids for neuropathic pain?
tramadol (noradrenergic and serotoninergic effect) tapentadol (noradrenergic effect) These drugs are weak opioids
Why are strong opioids recommended only as second/third line despite established efficacy?
Potential risk for long-term abuse
What is the efficacy of lidocaine plaster like?
Regional suppression of ectopic activity and antiallodynic device effect.
When is lidocaine commonly used?
First-line treatment for PHN in elderly patients and second line in other localized neuropathic pain (diabetic polyneuropathy and neuroma).
How effective are cannabinoids on neuropathic pain?
0 evidence for effectiveness of cannabinoids on neuropathic pain
Conclusions regarding neuropathic pain treatment:
Neuropathic pain is unresponsive to analgesics effective in nociceptive pain In neuropathic pain TCAs, SNRIs, and alpha-2-delta modulators are first-line treatments. Topical treatments offer new options with limited systemic effects Opioids are effective but risk profile limits use Combination therapy is promising but not always the best option.
Treatments of neuropathic pain: