A 68-year-old woman with metastatic breast cancer presents to the palliative care unit with severe, constant pain in her right chest wall and back, radiating in a dermatomal distribution. She has been on morphine 30 mg twice daily for 2 weeks, but pain remains uncontrolled (pain score 8/10). Physical examination reveals allodynia and hyperalgesia over the T4–T6 dermatomes. Imaging confirms metastatic involvement of the right T5 vertebral body with epidural extension. Her renal function is normal (eGFR 65 mL/min/1.73 m²). Which of the following is the most appropriate next step in pain management?

Explanation

## Cancer Pain Management: Neuropathic Component with Inadequate Opioid Response ### Clinical Context This patient has **mixed pain**: nociceptive (bone metastasis) + neuropathic (nerve compression/invasion). The dermatomal distribution, allodynia, and hyperalgesia indicate significant neuropathic involvement. **Key Point:** Neuropathic pain in cancer responds poorly to opioids alone. Adjuvant agents (gabapentinoids, SNRIs, tricyclic antidepressants) are essential for optimal control. ### Pain Management Algorithm for Cancer Pain with Neuropathic Features ```mermaid flowchart TD A[Cancer pain with neuropathic features]:::outcome --> B{Opioid dose adequate?}:::decision B -->|No| C[Escalate opioid dose]:::action B -->|Yes| D[Consider adjuvant agents] D --> E[Gabapentinoid or SNRI]:::action E --> F[Reassess in 1 week]:::decision F -->|Improved| G[Continue and optimize]:::action F -->|Inadequate| H[Consider interventional techniques]:::decision H -->|Suitable| I[Epidural analgesia or nerve block]:::action H -->|Not suitable| J[Escalate systemic therapy]:::action ``` ### Why Adjuvant Therapy Is Essential Here | Feature | Implication | | --- | --- | | Dermatomal distribution | Suggests nerve root or epidural involvement | | Allodynia + hyperalgesia | Hallmarks of neuropathic pain | | Poor response to morphine 30 mg BD | Opioid-resistant neuropathic component | | Normal renal function | Safe to use gabapentinoids | **High-Yield:** The combination of opioid escalation + adjuvant agent is the standard approach for mixed cancer pain. Adjuvants can reduce opioid requirements and improve overall control. ### Rationale for Correct Answer 1. **Opioid escalation alone is insufficient** — neuropathic pain requires adjuvant therapy 2. **Gabapentin or pregabalin** — first-line adjuvants for cancer-related neuropathic pain 3. **Concurrent opioid increase** — addresses the nociceptive component 4. **Renal function permits gabapentinoids** — eGFR 65 allows standard dosing **Clinical Pearl:** In cancer pain with neuropathic features, the combination of opioids + gabapentinoids often achieves better pain control than opioid escalation alone, and may even reduce total opioid dose over time. ### Why Interventional Techniques Are Not First-Line Here - Epidural analgesia is reserved for refractory pain despite optimized systemic therapy - This patient has not yet had a trial of adjuvant agents - Epidural placement carries procedural risk in metastatic disease [cite:Harrison 21e Ch 384; Oxford Textbook of Palliative Medicine]