Neuropathic Pain

Question 1

What is neuropathic pain?

Answer 1

Pain caused by a lesion or disease of the somatosensory nervous system (clinical description, not diagnosis)

Question 2

How does nervous system damage cause neuropathic pain?

Answer 2

• Increased nerve cell firing
• Decreased inhibition of neuronal activity in central structures
• Intact circuitry at the central level but with sensitization

Question 3

Presentation of neuropathic pain

Answer 3

• Spontaneous transmission (continuous or intermittent)
• Hyperalgesia (increased pain)
• Allodynia (pain from mundane stimuli)

Question 4

What is the goal in neuropathic pain?

Answer 4

Reducing/stabilizing nervous system activity
- Eliminating pain is not realistic
- May take days to weeks

Question 5

TCAs

Answer 5

Secondary - nortriptyline, desipramine
Tertiary - amitriptyline, imipramine
- Most data, QD dosing, can treat insomnia/depression
- Delayed onset, anticholinergic (AVOID IN ELDERS), cardiotoxic

try for 6-8 weeks, 2 weeks at max dose
25mg/day, up to 150mg/day

Question 6

SNRIs

Answer 6

Duloxetine (FDA approved), Venlafaxine
- can treat depression, better ADE profile
- serotonin syndrome, duloxetine CI in hepatic impairment
D: 30mg/day, up to 120mg/day
V: 37.5mg/day, up to 225mg/day

Question 7

What is Milnacipran?

Answer 7

SNRI for fibromyalgia
- well tolerated, can improve fatigue and energy
- BID, HTN

12.5mg/day, up to 100mg BID
titrate to 50mg BID after a week

Question 8

Gabapentin

Answer 8

• Few ADRs, DDIs
• FDA approved for postherpetic neuralgia (PHN)
• Mild CNS depression, significant with toxicity
• Renal dosing

Question 9

Pregablin

Answer 9

Control V (dependency, euphoria)
- Few ADRs, DDIs
- FDA approved for PHN, PDN (diabetic), fibromyalgia
- Mild CNS depression, significant with toxicity
- Renal dosing

Question 10

Tramadol

Answer 10

Works like an opioid (mu agonist)
- Less respiratory depression
- mu + SNRI effects = treats nociceptive pain AND neuropathic pain
- DDI with carbamazepine, quinidine, TCA, SSRI
- Serotonin syndrome
- Dizziness, constipation, GI, seizures (like opioids)
- Abuse potential (but less?)

IR 50mg q4h prn
ER 100mg up to 300mg/day

Question 11

Tapentadol (Nucynta)

Answer 11

For PDN (painful diabetic neuropathy)
- No active metabolites
- Schedule II, expensive
- Not really used

Question 12

Capsaicin

Answer 12

Depletes and prevents re-accumulation of substance P in periphery
- FDA approved, long term use
- Application issues (not for sensitive tissues)
- Qutenza 8% - 60 min of use every 3 months (how was this approved?)
- 0.025% patch and cream (zostrix) available

Question 13

Lidocaine

Answer 13

For PHN, topical anesthesia (off-label)
- 5-10 minute onset, variable duration
- Rx 5% patches hardly different from OTC 4% patches

Question 14

What is ZTlido?

Answer 14

1.8% lidocaine
- stays in place better

Question 15

What is 1st line for neuropathic pain?

Answer 15

TCAs, SNRIs, Gabapentanoids, Topicals (focal NP)

4-6 week trial

Question 16

What is 2nd line for neuropathic pain?

Answer 16

Tramadol, Combination 1st line therapies

4-6 week trial

Question 17

What is 3rd line for neuropathic pain?

Answer 17

SSRIs/Anticonvulsants
NMDA antagonists
Interventional therapies

Question 18

T/F: Opioids should be used for neuropathic pain

Answer 18

FALSE: they are very far down on the guidelines, avoid

Question 19

PDN treatment

Answer 19

TCAs, SNRIs, gabapentanoids, sodium-channel blockers

Question 20

PHN treatment (reactivation of variella-zoster)

Answer 20

Lidocaine** - FDA approved
TCAs, gabapentin, pregablin, valproate, tramadol, opioids (not really), capsaicin

Question 21

Low back pain treatment

Answer 21

APAP/NSAIDs 1st line acutely
Muscle relaxants
Tramadol/duloxetine

AVOID opioids long term
AVOID TCAs, SSRIs - not effective

Question 22

Fibromyalgia

Answer 22

• Sensitive to temperature
• Constant dull ache in all 4 quadrants
• Fatigue and sleep problems

Question 23

Fibromyalgia treatment

Answer 23

CBT* with other psychiatric problems

Duloxetine, Pregablin, Tramadol