Neuropathic pain Flashcards
what is neuropathic pain?
abnormal functioning of the sensory nerves delivering abnormal and painful signals to the brain.
examples and symptoms of neuropathic pain
causes:
1. Postherpetic neuralgia from shingles is in the distribution of a dermatome and usually on the trunk (after shingles/chicken pox)
2. Nerve damage from surgery
3. Multiple sclerosis
4. Diabetic neuralgia typically affects the feet
5. Trigeminal neuralgia
6. Complex Regional Pain Syndrome (CRPS)
7. lumbosacral radicular pain
8. brachial plexus injury
symptoms:
burning, tingling, pins and needles, electric shock, loss of sensation to touch in that affected area
what is the DN4 questionairre?
used to asesss the characteristics of hte pain and examinatoin of the affected area
score pain /10
>4/10 indicated neuropathic pain
how do we manage neuropathic pain
Amitriptyline is a tricyclic antidepressant
Duloxetine is an SNRI antidepressant
Gabapentin is an anticonvulsant
Pregabalin is an anticonvulsant
other options
Tramadol ONLY as a rescue for short term control of flares
Capsaicin cream (chilli pepper cream) for localised areas of pain
Physiotherapy to maintain strength
Psychological input to help with understanding and coping
trigeminal neuralgia
ophthalmic (v1)
maxillary (v2)
mandibular (v3)
unilateral lancinating pain that affects the V nerve.
(rare to get bilateral)
V2 and V3 are the most common. increaes with incidence.
triggering factors
causes- unclear or compression of the nerve. 5-10% of people have MS (think!V1)
symptoms: intense and spontaneous facial pain, electric-like shooting pain that can worsen over time. cold weather, spicy food, caffeine and citrus fruit makes it worse. can last a few seconds to one hour.
diffs: MS, tumor, AV malformation
mx: carbamazepine is 1st line
what is a complex regional pain syndrome
abnormal nerve functioning that causes neuropathic pain and abnormal sensations
usually just isolated to one limb and is often triggered by injury
can become painful, hypersensitivity (e.g. even to clothing) swell, change colour, temperature, flush with blood, abnormal sweating, abnormal hair growth
*treatment guided by pain specialist.
acute vs chronic pain
pain- “Pain is an unpleasant sensory and emotional experience arising from actual or potential tissue damage, or described in terms of such damage. Pain is always subjective.”
acute pain- warning signal for actual or potential tissue damage. associated with trauma, surgery, illness
chronic pain is pain that lasts beyond the normal tissue healing time. three-six months. no protective role in preventing further damage. can be considered a disease entity in its own right.
pain management
multimodal approach
analgesic drugs, physical therapy, behavioural therapy, interventional and surgical methods
WHO analgesic ladder
3-step algorithm for managing acute and chronic pain
principles are regular analgesia by mouth and clock with appropriate PRN meds. if PRN is needed >3x/d then inadequate analgesia is likely.
step 1: mild pain= non-opioid analgesics and adjuvant drugs
step 2: moderate pain= non-opioid analgesics, mild opioid and adjuvant drugs (codeine)
step 3: severe pain= non-opioid analgesics, strong opioid, adjuvant drug (tramadol)
types of pain
1. nociceptive
- nociceptive: triggered by a chemical, mechanical or thermal stimuli. the inflamamtion, tissue damage, IL-cytokines activates the nociceptor pathway (sponothalamic…)
1a: somatic pain (MSK). pain caused by abnormal neural activity that arises secondary to injury and quality (alpha fibres)
1b: visceral pain: diffuse, dull and deep pain (c fibres)
types of pain
2. neuropathic
neuropathic pain: an abnormal neural activity that arises secondary to an injury, disease or dysfunction of the nervous system
examples: burning, shooting, dyaesthesia. occurs spontaenously/with non painful stimuli/greater than expected response.
2a) central pain: caused by CNS dysfunction (lesions produced by an ischaemic stroke, phantom limb pain)
2b) peripheral pain: damage to the peripheral nerves. diabetic neuropathy, postherpetic neuralgia
2c) sympathetically mediated pain: caused by damage to autonomic nerves
what is the physiology of pain?
nociceptors detect a chemical, mechanical or thermal noxious stimulus (tissue injury)
this is converted to an electrical signal (an action potential)
the c fibres or alpha fibres carry the afferent input to the dorsal horn of the spinal cord.
the secondary nociceptive neurons in the spinothalamic tract carry the afferent input to the thalamus in the CNS
pain perception and response is sent along the efferent pathways
painmodulateion
reaction
withdrawal reflex
a polysynaptic reflex that causes the body to move away from a painful stimulus via contraction of flexor muscles and relaxation of extensor muscles.
what is sensitization
abnormal pain perception due to increased neuronal sensitivity to a noxious stimulus (hyperalgesia) and or reduced neuronal threshold to otherwise a normal stimuli in response to injury, inflammation or repetitive stimulation
*role in chronic pain, neuropathic pain
physiology of sensitization
two mechanisms- periheral sensitisation and central sensitations
peripheral sensitiations
peripheral sensitations
injuy, inflammmation or repetiive stimulation of the peripheral nociceptive neurions causes al local release of chemical mediators (cytokines, nerve growth factors, histamine). repeated/prlonged exposure uregulates the ion channels so it increases sensitivty of the receptors or reduces their threshold. this causes increased action potential and therefore abnoramal pain perception
*suuall ceases once the itssue heals
central sensitization
injury/inflammation of the CNS (dorsal horn of spinal cord, brain). this causes increased excitability and reduced inhbition of the CNS and recuiremnt of non-nociceptive fibres (alpha fibers) into the nociceptive pathway
what is referred pain
pain that is percieved as a location rather than that of the causative stimulus. projectin of pain onto a specific dermatome/myotome of the corresponding segment of the pspinal cord
exampels of referred pain
Right shoulder pain in patients with cholecystitis or perforated PUD
Kehr’s sign: left shoulder pain associated with diaphragmatic irritation due to splenic rupture
Left-sided chest and arm pain: myocardial infarction
Periumbilical pain in the early stages of appendicitis
referred pain overveiw
Diaphragm, C4= Shoulders
Heart, Th3–4= Left chest
Esophagus, Th4–5 = Retrosternal
Stomach Th6–9= Epigastrium,
Liver, gallbladder, Th10–L1= Right upper quadrant
Small bowel, Th10–L1= Periumbilical
Colon, Th11–L1= Lower abdomen
Bladder, Th11–L1= Suprapubic
Kidneys, testicles, Th10–L1 = Groin
what is phantom limb pain
the sensation that the amputated limb is still patially or totally existent. can cause sensation of pain. intermitttent (burning, tingling, shooting, itching, squeezing)
treatment: mirror therapy transcutaenous electrical nerve stimulation NMDA receptor antagonist adjuvant therapy (TCA, anticonvulsant)
prophylaxis: peri op regional anaesthesia
ICD-11 defined 8 major categories of chronic pain
chronic primary pain chronic cancer-related pain chronic postsurgical or post-traumatic pain chronic secondary visceral pain chronic secondary musculoskeletal pain chronic neuropathic pain chronic secondary headache or orofacial pain other specified chronic pain
a consequence of chronic pain
physical- sensitisation, sleep abnormalities, disuse/posture abnormalities
psychological: frustration, low self-esteem
social / occupational
post herpetic neuralgia
pain >3 months after herpes zoster eruption (chicken pox / shingles)
symptoms of unilateral neuropathic pain: hyperalgesia, allodynia (pain from a stimulus that normally isn’t painful e.g my hair hurts, itching
central sensitivity syndromes
FMS- fibromyalgia syndrome CFS- chronic fatigue syndrome IBS POTS- Postural tachycardia syndrome hypermobile EDS type
what is the difference between nociceptive pain and neuropathic pain
nociceptive pain is also known as physiological or inflammatory pain. there is an obvious tissue injury or illness and protective function. can be sharp or dull and well localised
nociception is how signals get from the site of injury to the brain but pain perception is ho we ‘feel’ pain and that can be influenced by beliefs, psychological factors, culutral issues, social factors, personality or other illnesses.
neuropathic pain is when there is nervous system damage or abnormality. there may not be an obvious tissue injury and is not a protective functoin. burning, shooting, numbness, pins and needles. not well localised.
what is the physiology of pain
- tissue injury
- release of chemicals which stimulates pain receptors (nociceptors) and signals travel in alpha or c nerve to the spinal cord.
- dorsal horn is the first relay station. synapse with second-order neurone which travels up the opposite side of the spinal cord
- thalamus is the second relay station. connects cortex, limbic system and brainstem this is where pain perception occurs.
- descending pathway from the brain to the dorsal horn. usually inhibits pain signals from the periphery.
what is the physiology of neuropathic pain
abnormality of peripheral nerves, spinal cord or brain
abnormal nerve tissue- amputation neuroma
the abnormal firing of pain nerves
changes in chemical signalling in the dorsal horn
abnormal nerve connections in the dorsal horn
loss of normal inhibitory functino
drug classification (again)
Simple analgesics
- Paracetamol (acetaminophen)
- Anti-inflammatory medicines
eg. Diclofenac, ibuprofen
Opioids
Mild: Codeine
Strong: Morphine, pethidine, oxycodone
others: tramadol, TCA, anticonvulsant, ketamine, local anaesthetic, clonidine
periphery tx: non-drug treatments (rest, ice, compression, elevation), anti-inflammatories and local anaesthetics
spinal cord tx: non-drug treatment like acupuncture, massage, local anaesthetics, opioids and ketamine
brain: psychological, paracetamol, opioids, amitryptiline, clonidine.
“RAT” approach
recognise:
assess: severity, type, other factors
- severity:
pain score at restand on movement (verbal, numerical, visual VAS or faces)
how is it affecting the patient- moving, coughing, working - type:
acute / chronic
cancer/ non cancer
nociceptive / neuropathic - other factors
physical, psychological, social, anger, anxiety, depression, lack of social support
treat- nondrug/drug RICE (Rest, Ice, Compression, Elevation) nursing care surgery, acupuncture, massage psychological
drug: mild, mod, severe
then reasses- is this working?
alpha and c fibres pain condution
fast resopnse: alpha fibres, large myelinated. up to 10m/sec. sharp and stabbing pain
slow repsonse: c fibres, small unmyelinated. 1.2m/sec, aching burning pain
what is trigeminal neuralgia
condition characterised by attacks of facial paining one area or more of the branches of the trigeminal nerve
v1 opthalic
v2 maxillary
v3 mandibular
clinical features of trigeminal neuralgia
unilateral facial pain. severe, intense pain with sharp and stabbing quality that can last for several seconds. can occur up to 100 times per day. shoots from mouth to the angle of the jaw.
can be unprovoked or triggered by an innocuous stimuli like chewing, talking, touch, brushing teeth, washing face.
facial spasms can occur
psychological distress
causes of trigeminal neuraligia
classical trigeminal neuralgia (CTN) is caused by neruvoascualr compression of the trigeminal nerve root usually by an aberrant loop of a neighbouring artery (e.g. the superior cerebellar artery) dislocation or atrophy of the trigeminal nerve root.
secondary trigeminal neuralgia (STN) is caused by an underlying condition (MS), tutor, cerebellopontine angle, AVM
no identifiable cause is referred to as idiopathic trigeminal nerualgia. unremarkable findings onen RI and electrophysiological tests
management options for trigeminal neuralgia
anticonvulsants (carbamazepine)
(oxcarbazepine)
other anticonvulsants- lamotrigine, baclofen, phenytoin, gabapentin
in acute exacerbation consider lidocaine infusion, oral or nasal lidocaine, sumatriptan
microvascular decompression (MVD) a piece of sponge like material is placed between the blood vessel and nerve.
transcutaenous procedures
radiofrquency ablation
diagnostic criteria for trigeminal neuralgia
MRI at least once in lifetime to evaluate structural etiology (CT if contraindicated)
- recurring unilateral facial pain in the area innervated by one or more divisions of the trigeminal nerve
- pain characteristic
- severe
- lasting no more than 2 mins
- quality is sharp, shooting, stabbing, electric shock
additional investigations:
electrophysiological trigeminal reflex measurement
