Neuropathic pain

Question 1

what is neuropathic pain?

Answer 1

abnormal functioning of the sensory nerves delivering abnormal and painful signals to the brain.

Question 2

examples and symptoms of neuropathic pain

Answer 2

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

Question 3

what is the DN4 questionairre?

Answer 3

used to asesss the characteristics of hte pain and examinatoin of the affected area

score pain /10
>4/10 indicated neuropathic pain

Question 4

how do we manage neuropathic pain

Answer 4

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

Question 5

trigeminal neuralgia

Answer 5

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

Question 6

what is a complex regional pain syndrome

Answer 6

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.

Question 7

acute vs chronic pain

Answer 7

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.

Question 8

pain management

Answer 8

multimodal approach

analgesic drugs, physical therapy, behavioural therapy, interventional and surgical methods

Question 9

WHO analgesic ladder

Answer 9

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)

Question 10

types of pain

1. nociceptive

Answer 10

1. 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)

Question 11

types of pain

2. neuropathic

Answer 11

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

Question 12

what is the physiology of pain?

Answer 12

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

Question 13

withdrawal reflex

Answer 13

a polysynaptic reflex that causes the body to move away from a painful stimulus via contraction of flexor muscles and relaxation of extensor muscles.

Question 14

what is sensitization

Answer 14

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

Question 15

physiology of sensitization

Answer 15

two mechanisms- periheral sensitisation and central sensitations

Question 16

peripheral sensitiations

Answer 16

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

Question 17

central sensitization

Answer 17

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

Question 18

what is referred pain

Answer 18

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

Question 19

exampels of referred pain

Answer 19

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

Question 20

referred pain overveiw

Answer 20

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

Question 21

what is phantom limb pain

Answer 21

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

Question 22

ICD-11 defined 8 major categories of chronic pain

Answer 22

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

Question 23

a consequence of chronic pain

Answer 23

physical- sensitisation, sleep abnormalities, disuse/posture abnormalities

psychological: frustration, low self-esteem

social / occupational

Question 24

post herpetic neuralgia

Answer 24

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

Question 25

central sensitivity syndromes

Answer 25

FMS- fibromyalgia syndrome
CFS- chronic fatigue syndrome
IBS
POTS- Postural tachycardia syndrome
hypermobile EDS type

Question 26

what is the difference between nociceptive pain and neuropathic pain

Answer 26

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.

Question 27

what is the physiology of pain

Answer 27

1. tissue injury
2. release of chemicals which stimulates pain receptors (nociceptors) and signals travel in alpha or c nerve to the spinal cord.
3. dorsal horn is the first relay station. synapse with second-order neurone which travels up the opposite side of the spinal cord
4. thalamus is the second relay station. connects cortex, limbic system and brainstem this is where pain perception occurs.
5. descending pathway from the brain to the dorsal horn. usually inhibits pain signals from the periphery.

Question 28

what is the physiology of neuropathic pain

Answer 28

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

Question 29

drug classification (again)

Answer 29

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.

Question 30

“RAT” approach

Answer 30

recognise:

assess: severity, type, other factors

1. severity:
   pain score at restand on movement (verbal, numerical, visual VAS or faces)
   how is it affecting the patient- moving, coughing, working
2. type:
   acute / chronic
   cancer/ non cancer
   nociceptive / neuropathic
3. 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?

Question 31

alpha and c fibres pain condution

Answer 31

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

Question 32

what is trigeminal neuralgia

Answer 32

condition characterised by attacks of facial paining one area or more of the branches of the trigeminal nerve

v1 opthalic
v2 maxillary
v3 mandibular

Question 33

clinical features of trigeminal neuralgia

Answer 33

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

Question 34

causes of trigeminal neuraligia

Answer 34

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

Question 35

management options for trigeminal neuralgia

Answer 35

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

Question 36

diagnostic criteria for trigeminal neuralgia

Answer 36

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