Neuropathic Pain Management

Definition & Pathophysiology - Nerve Wreckage 101

• Definition (IASP): Pain caused by a lesion or disease of the somatosensory nervous system.
• Key Mechanisms:
  • Peripheral Sensitization: ↑ responsiveness, ↓ threshold of nociceptive neurons in the periphery.
  • Central Sensitization: ↑ excitability of neurons in the CNS (spinal cord, brain); involves wind-up, long-term potentiation.
  • Ectopic Discharges: Spontaneous pathological firing from damaged primary afferent neurons or their axons.
  • Channelopathy: Altered expression/function of ion channels (e.g., Na⁺, Ca²⁺ channels like Nav1.7, Nav1.8).
  • Neuroinflammation: Activation of glia (microglia, astrocytes) releasing pro-inflammatory mediators.

⭐ Allodynia (pain due to a stimulus that does not normally provoke pain) is a hallmark feature of neuropathic pain, often indicating central sensitization mechanisms at play_._

Clinical Features & Diagnosis - Pinpointing the Pain

• Key Symptoms: Burning, shooting, electric shocks, pins & needles, numbness. Often worse at night.
• Key Signs:
  • Allodynia (pain from light touch).
  • Hyperalgesia (↑ pain response).
  • Sensory deficits (touch, vibration).
• Clinical Examination: Assess sensory modalities (light touch, pinprick, temperature, vibration), reflexes, and motor strength.
• Screening Tools:

  Tool	NP if Score
  DN4	≥ 4
  LANSS	≥ 12
  PainDETECT	≥ 19 (likely NP)

⭐ Painful diabetic neuropathy is the most common type of neuropathic pain.

First-Line Pharmacotherapy - The Go-To Arsenal

Second & Third-Line Agents - Backup Brigade

• Opioids (Use with caution):

  • Tramadol: Weak µ-opioid agonist; serotonin-norepinephrine reuptake inhibitor (SNRI). Risks: Serotonin syndrome, ↓seizure threshold.
  • Tapentadol: µ-opioid agonist & norepinephrine reuptake inhibitor (MOR-NRI). Fewer GI side effects than typical opioids.

• Topical Agents:

  Agent	MOA	Key Uses & Application
  Lidocaine 5% Patch	Blocks Na+ channels, ↓ectopic firing	Post-herpetic neuralgia (PHN). Max 3 patches; 12h on/12h off.
  Capsaicin Cream/Patch	TRPV1 agonist, desensitizes C-fibers	PHN, diabetic neuropathy. Apply with gloves.

• Other Anticonvulsants:

  • Lamotrigine: Na+ channel blocker. Adjunct for refractory pain.
  • Carbamazepine: Na+ channel blocker.

    ⭐ Carbamazepine is the drug of choice for trigeminal neuralgia.

Non-Pharma & Interventions - Holistic Help

• Non-Pharmacological:
  • Physiotherapy: Enhances mobility, reduces pain.
  • TENS (Transcutaneous Electrical Nerve Stimulation): For localized relief.
  • CBT (Cognitive Behavioral Therapy): Modifies pain perception & coping.
  • Acupuncture: Traditional method, may modulate pain.
• Interventional (refractory pain):
  • Nerve blocks: Diagnostic or therapeutic (e.g., local anesthetics).
  • Spinal Cord Stimulation (SCS): Neuromodulation for persistent pain.
  • Intrathecal drug delivery: Targeted CNS analgesia (e.g., opioids).

⭐ TENS is a commonly used non-invasive modality for localized neuropathic pain, often as an initial non-pharmacological approach.

High‑Yield Points - ⚡ Biggest Takeaways

• First-line: TCAs (Amitriptyline), SNRIs (Duloxetine), Gabapentinoids (Pregabalin, Gabapentin).
• Amitriptyline: Effective, but notable anticholinergic side effects, especially in elderly.
• Duloxetine: Good for painful diabetic neuropathy; also an antidepressant.
• Gabapentin/Pregabalin: Act on α2-δ Ca²⁺ channels; common side effects: sedation, dizziness.
• Carbamazepine: Drug of choice for trigeminal neuralgia.
• Tramadol/Tapentadol: Weak opioids with SNRI activity; second-line options.
• Topical Lidocaine: Useful for localized neuropathic pain.