Pathophysiology of pain - nociceptive

Definition

Nociceptive pain arises from activation of peripheral pain receptors (nociceptors) by actual or threatened tissue damage - the normal, expected physiological pain response to injury, inflammation, or disease affecting tissue with intact nerve pathways
The most common pain mechanism in cancer and many other conditions, typically responding well to standard analgesics following the WHO analgesic ladder

Divided into somatic (nociceptors in skin, muscle, bone, joints - typically well-localised, described as sharp/aching/throbbing) and visceral (nociceptors in internal organs - typically poorly localised, described as deep, dull, cramping, sometimes referred to a distant somatic site) - the distinction matters because the two can respond somewhat differently to specific interventions

Clinical assessment (character, location, aggravating/relieving factors) usually distinguishes nociceptive pain from neuropathic pain based on descriptor and distribution alone, without needing specialised investigation - "aching, throbbing, well-localised" (somatic) or "deep, cramping, poorly localised, sometimes referred" (visceral) both point toward a nociceptive mechanism, in contrast to the burning/shooting/electric qualities of neuropathic pain

Responds well to the WHO analgesic ladder (paracetamol, NSAIDs where appropriate, then opioids) in a stepwise fashion matched to severity
Bone pain specifically often benefits from NSAIDs (if not contraindicated) and, for localised sites, radiotherapy, in addition to systemic analgesia
Visceral pain from obstruction/distension may respond to antispasmodics (e.g. hyoscine butylbromide) in addition to standard analgesia

Bone metastases (somatic nociceptive), bowel obstruction (visceral nociceptive), the WHO analgesic ladder

Nociceptive pain is generally the most straightforward pain mechanism to treat effectively with standard analgesics - persistent pain despite an adequately titrated analgesic ladder should prompt reconsideration of whether a neuropathic or other component is also present

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