Red flags
- New back pain + neurological signs (weakness, sensory level, sphincter disturbance) -> spinal cord compression - emergency, MRI within 24h
- Sudden severe headache or new focal neurology -> cerebral metastasis with bleed/raised ICP
- Bone pain + hypercalcaemia symptoms (confusion, constipation, polyuria) -> malignant hypercalcaemia
- Pain with fever in a neutropenic patient -> neutropenic sepsis pathway takes priority
- Sudden severe pain at a known bone metastasis site -> pathological fracture
Differential by mechanism
By pain mechanism - determines analgesic choice
- Nociceptive somatic - bone metastases, soft tissue infiltration - well-localised, aching/throbbing
- Nociceptive visceral - hepatic capsule stretch, bowel obstruction - poorly localised, cramping/deep
- Neuropathic - nerve/plexus infiltration or compression, chemotherapy-induced peripheral neuropathy - burning, shooting, allodynia
- Breakthrough pain - transient exacerbation on a background of otherwise controlled pain, +/- predictable triggers (incident pain e.g. movement, weight-bearing)
Non-mechanical contributors
- Total pain concept - psychological distress, spiritual/existential distress, social factors all amplify perceived pain and must be addressed alongside pharmacology
- Treatment-related pain - mucositis, post-surgical, radiation-induced
Focused history
- Site, character, radiation, temporal pattern (constant vs breakthrough), severity (validated scale)
- Aggravating/relieving factors - movement (bone), eating (visceral), position
- Current analgesic regimen, response, side effects, adherence
- Impact on function, sleep, mood
- Screen for red flag features (above) at every assessment, not just at first presentation
- Psychosocial and spiritual distress - part of comprehensive assessment, not an afterthought
Focused examination
- Localise the pain generator - palpate for tenderness, examine the relevant dermatome/myotome if neuropathic pain suspected
- Full neurological exam if any suggestion of cord/nerve root compression - do not skip this in back pain
- Abdominal exam if visceral pain suspected (hepatomegaly, obstruction signs)
- Signs of opioid toxicity (sedation, myoclonus, pinpoint pupils, reduced respiratory rate) at every review
Investigation strategy
- Directed by the suspected pain generator and red flags, not routine imaging for all pain
- Urgent MRI spine for any suspected cord compression
- Bone scan/CT/MRI for suspected new bony metastasis causing localised pain
- Bloods - calcium (hypercalcaemia as a pain amplifier and red flag), renal function (guides opioid choice/dose adjustment)
Management
A. WHO analgesic ladder - still the organising framework, now used more flexibly
- Mild pain: non-opioid (paracetamol, NSAID if not contraindicated)
- Moderate pain: weak opioid (or low-dose strong opioid, increasingly preferred over historical step 2 agents) +/- non-opioid/adjuvant
- Severe pain: strong opioid (morphine, oxycodone, hydromorphone) titrated to effect - no ceiling dose, titrate against analgesia vs side effects
- Modern practice often moves directly to low-dose strong opioids for moderate-severe pain rather than strictly stepping through weak opioids
B. Opioid principles
- Immediate-release for titration and breakthrough dosing; convert to modified-release once stable dose established
- Breakthrough dose = ~1/6 to 1/10 of total daily opioid dose, available PRN
- Anticipate and manage side effects proactively - prescribe a laxative with every opioid (constipation near-universal, does not tolerate), antiemetic for initial nausea, monitor sedation
- Renal impairment - avoid morphine accumulation (active metabolites); fentanyl or buprenorphine preferred
C. Adjuvant analgesics by mechanism
- Bone pain: NSAIDs, bisphosphonates or denosumab (also reduce skeletal-related events), radiotherapy for localised refractory bone pain, corticosteroids
- Neuropathic pain: gabapentinoids (gabapentin, pregabalin), or tricyclic antidepressants (amitriptyline), or duloxetine
- Raised ICP/nerve compression oedema: dexamethasone
- Visceral/obstruction-related: antispasmodics, corticosteroids, octreotide for bowel obstruction symptoms
D. Interventional and non-pharmacological options for refractory pain
- Nerve blocks (e.g. coeliac plexus block for pancreatic cancer pain), vertebroplasty for painful vertebral collapse, palliative radiotherapy for localised bone pain
- Psychological support, physiotherapy, integrative approaches alongside pharmacology
E. Total pain approach
- Address psychological, social, spiritual distress concurrently - palliative care team involvement early for complex or refractory pain, not only at end of life
Traps
- Missing spinal cord compression because back pain was attributed to "known bone metastases" without a neurological exam
- Under-dosing opioids from fear of dependence/respiratory depression in a patient with genuine severe cancer pain - tolerance and titration make this manageable
- Forgetting to co-prescribe a laxative with an opioid
- Treating all pain as nociceptive and missing a neuropathic component that needs an adjuvant, not just more opioid
- Not involving palliative care early because pain is seen as a purely pharmacological problem
Talk track
Classify pain by mechanism first (somatic, visceral, neuropathic, breakthrough) - it determines which drug class helps. Titrate opioids without a ceiling against analgesia vs side effects, always with a laxative co-prescribed, and add mechanism-matched adjuvants (bisphosphonates/radiotherapy for bone, gabapentinoids for neuropathic, dexamethasone for compression-related oedema). Screen for red flags (especially cord compression) at every pain assessment, and address the psychological and social dimensions of total pain alongside the pharmacology.
Study aid only. These notes are written with the help of AI. Not for guiding clinical decisions.