21 - Neuropathic Pain

Question 1

Presentation and diagnosis of neuropathic pain

Answer 1

• Pain reported often not evident by physical assessment
• Common descriptors = shooting, burning, electric shock, pins and needles, allodynia, hyperalgesia
• DN4 questionnaire most common
• • If score 4 or greater, test is positive (83% sensitivity, 90% specificity)

Question 2

What determines tx choice for neuropathic pain?

Answer 2

• Efficacy (little efficacy data)
• • Greatest evidence for painful diabetic neuropathy (PDN) and post-herpetic neuralgia b/c more common so more research is done
• Px goals
• • What function means to the pt and degree of change
• Desire for specific harm avoidance
• Comorbidities
• Feasibility

Question 3

Opioids for PDN

Answer 3

• Very low-quality evidence proving value in tx
• Overall not used b/c potential for dependence and abuse
• Tramadol
• • MOA = weak m-opioid receptor agonist activity and inhibition of NE/5-HT reuptake
• • Although has a lower potential for abuse compared w/ other opioids, given the safety concerns it isn’t recommended as 1st or 2nd line agent

Question 4

Harms of TCAs for neuropathic pain **know this

Answer 4

• Notable SE (~10-30%) = anticholinergic, weight gain, sedation, orthostatic hypotension
• Cautions = elderly, dementia, glaucoma, urinary retention, cardiac disease
• Nortriptyline has fewer SE

Question 5

Harms of gabapentin and pregabalin for neuropathic pain **know this

Answer 5

• Notable SE = dizziness, sedation, peripheral edema (don’t want to treat this w/ a diuretic; often have to switch if edema becomes bothersome)
• Cautions = elderly, existing edema, fall risk, abuse potential

Question 6

Harms of SNRIs for neuropathic pain **know this

Answer 6

• Notable SE = nausea (particularly for venlafaxine), increased BP, dizziness
• Cautions = HTN, bipolar disorder

Question 7

Harms of tramadol for neuropathic pain **know this

Answer 7

• Notable SE = nausea, constipation, sedation, dizziness

- Cautions = opioid dependence/addiction risk, seizure risk

Question 8

Non-pharms for neuropathic pain

Answer 8

• Behavioural, psychosocial, physical and other therapies are essential for long-term management
• Interdisciplinary intervention may decrease drug requirements
• Exercise, relaxation, CBT, music therapy
• Overall DM2 benefit and decreased CV risk
• Decreased neuropathic sx?
• Muscle strengthening & balance to reduce falls?

Question 9

Neuropathic pain meds – specifics

Answer 9

• Most drugs require a trial of 2-4 weeks; usually try 4 weeks
• *Let px know this is a slow process
• Fast track = increase dose by 50-100% q3days
• Cautious = increase dose by 50-100% q1week

Question 10

Dosing of pain meds for neuropathic pain

Answer 10

• Always start low and go slow (this is a chronic condition and not worth risking harm to the pt)
• SE may result in a loss of a viable option in the mind of the pt
• Higher doses have a low likelihood of resulting in greater benefit and are more likely to result in greater harm

Question 11

Common comorbidities w/ neuropathic pain and possible drugs for both conditions

Answer 11

• *If someone is stable on a drug for one condition, never switch just because it might help w/ another condition; only use this when starting new meds
• Depression/anxiety -> SNRI, TCA?
• Insomnia -> TCA, gabapentin?
• Osteoarthritis -> duloxetine, tramadol?
• Migraine -> TCA
• Most other types of neuropathic pain -> SNRI, TCA, gabapentin, pregabalin, tramadol?

Question 12

What should be monitored for neuropathic pain? **know this

Answer 12

• Efficacy -> pain level, functioning (mobility, exercise tolerance, sleep, socialization, psychological status)
• Safety (SE) **also includes driving & fall risk

Question 13

When should you monitor for neuropathic pain? **know this

Answer 13

Depends on rate of titration desired and self-management abilities of pt

Question 14

Combination therapy for neuropathic pain

Answer 14

• Studies generally small w/ some questionable methodology
• Some combos w/ some positive data:
• • Gabapentin + nortriptyline
• • Gabapentin + opioid -> for the study, NNT = NNH plus concerns w/ long-term opioid use
• • Topical amitriptyline + ketamine

Question 15

Topicals for neuropathic pain

Answer 15

• Lidocaine
• • 5% plaster or patch most studied -> modest benefit in low quality, short-term trials
• • 1st or 2nd line in several guidelines for PHN
• • Advantage -> immediate onset and minimal systemic absorption
• Capsaicin
• • 0.075% gel showed insufficient data to draw conclusions
• • 8% patch showed benefit but not available in Canada
• Ketamine alone -> case series supporting pain relief vs. placebo
• Amitriptyline + ketamine

Question 16

Points for pt education for shared decision-making

Answer 16

• Likelihood of benefit
• When to likely see a reliable benefit
• SE (what are they and how common are they; talk about what to do if they happen)
• Approx. cost
• If several reasonable options to choose from, which would the pt prefer based on these?

Question 17

Cannabis overview and terminology

Answer 17

• Cannabis = preferred term instead of marijuana; sativa, indica, and ruderalis
• • Used recreationally for euphoric effects; primary psychoactive component is THC
• • May use “recreational” cannabis for medicinal purposes (who is counselling them?)
• • Medicinal use based on recommendation/Rx by an appropriate HCP for a known medical condition that has evidence for efficacy
• Cannabinoids: chemical compounds that are active at cannabinoid receptors in the body; can be plant sourced or synthetic

Question 18

Indications for medical marijuana

Answer 18

• On-label = pain (cancer-related, neuropathic), MS-related spasticity, chemotherapy-induced N/V, anorexia (HIV/AIDS)
• Off-label = RA, spinal cord injury, epilepsy, insomnia, anxiety, etc.

Question 19

Components of cannabis (cannabinoids)

Answer 19

• THC – principal psychoactive component
• • Increases pleasure, appetite
• • Decreases memory, cognition
• *Analgesia
• Cannabidiol (CBD) = no psychoactivity
• • Antiemetic, antispasmodic properties
• • Analgesia, anti-inflammatory
• • Anti-anxiety
• Cannabinol (CBN) = mild psychoactivity
• • Anti-inflammatory
• • Immunosuppressive effects

Question 20

Commercial cannabinoids

Answer 20

• Nabilone -> oral capsule, semi-synthetic analogue of THC; chemotherapy induced N/V; AE = dizziness, drowsiness, dry mouth
• Sativex -> oromucosal spray containing THC and CBD; doesn’t produce a significant “high” unless at very high spray use; used for spasticity in MS
• *Generally preferred over cannabis due to safety and dosing predictability

Question 21

Who would be a candidate for cannabis?

Answer 21

• Not typically 1st or 2nd line therapy for any indication
• Reserve use for px who have failed 3 or more other therapies for neuropathic pain
• Relative CI = age < 21-25, hx of psychosis/ schizophrenia, or substance abuse hx
• • Doesn’t cause schizophrenia if you aren’t predisposed; can precipitate first episode sooner and can precipitate psychotic events
• Like opioids, should be prescribed as a trial and have an exit strategy in place

Question 22

Physiological effects of cannabis

Answer 22

• Timing depends on route (acute can begin w/in 30 seconds & last 4-12 hours)
• Acute -> memory impairment, motor coordination effects, psychosis, increased HR, increased risk of MI w/in 60 mins after smoking due to increased cardiac demand (caution w/ MI hx or those w/ other cardiac conditions), orthostatic hypotension, analgesia
• Chronic -> dependence, bronchitis/emphysema, increased risk of psychotic disorders, poor learning and memory recall
• • Adolescents (< 25 y/o) -> altered brain dev’t, cognitive impairment, poor educational outcomes

Question 23

Cannabis use disorder – signs, sx of withdrawal, and tx

Answer 23

• Signs of CUD during tx:
• • Wanting high potency THC only
• • Misuse of other substances
• • Poor functioning
• • Rapid or unsanctioned dose increased
• • Missed follow-up; reports of lost or stolen cannabis
• Sx of cannabis withdrawal (onset 1-2 days, peak 2-6 days) -> anger, aggression, appetite change, weight loss, anxiety, irritability
• Treating CUD -> brief interventions, withdrawal management, and psychosocial interventions