Neuropathic Pain Management

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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. Mechanisms of Neuropathic Pain

⭐ 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:
    ToolNP 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

FeatureTCAs (e.g., Amitriptyline)SNRIs (e.g., Duloxetine, Venlafaxine)Gabapentinoids (e.g., Pregabalin, Gabapentin)
MOANE & 5-HT reuptake ↓; receptor blockadeNE & 5-HT reuptake ↓Bind $\alpha_2\delta$-1 Ca$^{2+}$ channel subunit
Starting DoseAmitriptyline: 10-25 mg HSDuloxetine: 30 mg OD; Venlafaxine XR: 37.5 mg ODPregabalin: 25-75 mg BID; Gabapentin: 100-300 mg HS/TID
Common SEAnticholinergic, sedation, orthostasisNausea, dizziness, insomnia, ↑BP (Venlafaxine)Dizziness, somnolence, edema, weight gain
ConsiderationsCardiotoxicity risk (📌 Tri-C's); many interactionsMonitor BP (Venlafaxine); Duloxetine for DPNPRenal dose adjustment needed

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:

    AgentMOAKey Uses & Application
    Lidocaine 5% PatchBlocks Na+ channels, ↓ectopic firingPost-herpetic neuralgia (PHN). Max 3 patches; 12h on/12h off.
    Capsaicin Cream/PatchTRPV1 agonist, desensitizes C-fibersPHN, 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). Neuropathic Pain Pathways and Spinal Cord Stimulation

⭐ 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.

Practice Questions: Neuropathic Pain Management

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Flashcards: Neuropathic Pain Management

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Drug of choice for acute severe migraine is:

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