📋 Key Information Summary
- Pain is mechanistically classified into nociceptive, neuropathic, nociplastic, and mixed categories; accurate classification guides analgesic selection.
- Nociceptive pain arises from actual or threatened tissue damage activating peripheral nociceptors; examples include fracture, osteoarthritis, post-surgical pain, and visceral colic.
- Neuropathic pain results from disease or lesion of the somatosensory nervous system; common causes in Australia include diabetic peripheral neuropathy (DPN), post-herpetic neuralgia (PHN), and spinal cord injury.
- Nociplastic pain (previously "central sensitisation") arises from altered nociception without clear tissue damage or somatosensory lesion; fibromyalgia, irritable bowel syndrome, and non-specific chronic low back pain are prototypical.
- Mixed pain combines two or more mechanisms (e.g., nociceptive + neuropathic in lumbar radiculopathy or cancer pain) and is the most common clinical presentation in chronic pain.
- The DN4 questionnaire (≥4/10 suggests neuropathic pain) and painDETECT are validated screening tools recommended by the IASP and Australian Pain Society.
- Nociceptive pain responds to simple analgesics (paracetamol, NSAIDs) and opioids; neuropathic pain requires adjuvant agents — first-line: amitriptyline, duloxetine, pregabalin, or gabapentin.
- Nociplastic pain is best managed with multimodal non-pharmacological strategies (graded exercise, CBT, sleep hygiene) plus low-dose tricyclic antidepressants or SNRIs; opioids are ineffective and harmful.
- Opioids have a limited role in chronic non-cancer pain (CNCP) across all pain types; the 2020 RACGP/ Faculty of Pain Medicine PMRI guidelines recommend against long-term opioid use for CNCP.
- All neuropathic adjuvant analgesics require slow titration and renal/hepatic dose adjustment; PBS authority is required for pregabalin, duloxetine, and gabapentin for neuropathic pain.
- Aboriginal and Torres Strait Islander Australians experience a 1.4-fold higher burden of chronic pain with significantly reduced access to specialist pain services; culturally safe, community-based models are essential.
- Psychosocial contributors (yellow flags) must be assessed in every chronic pain presentation regardless of mechanism; untreated comorbid anxiety/depression worsens all pain types.
- Re-assess pain classification at each visit — pain mechanisms can evolve over time, and treatment should be adjusted accordingly.
Introduction & Australian Epidemiology
Pain is the most common reason Australians seek healthcare. The International Association for the Study of Pain (IASP, 2020 revised definition) defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage." Understanding the underlying mechanism of pain — rather than relying solely on duration (acute vs chronic) or anatomical location — is fundamental to rational analgesic prescribing and improved patient outcomes.
The IASP mechanistic classification recognises three primary categories: nociceptive, neuropathic, and nociplastic pain. In clinical practice, many patients present with mixed pain involving overlapping mechanisms. Accurate classification guides selection of analgesic classes, predicts treatment response, and helps set realistic patient expectations.
Australian Burden of Pain
- Approximately 3.24 million Australians (1 in 5) live with chronic pain (persistent pain > 3 months), costing an estimated 9.3 billion annually in direct healthcare, lost productivity, and carer costs (Painaustralia / Deloitte Access Economics, 2019).
- Neuropathic pain affects 7–10% of the general Australian population; post-herpetic neuralgia alone accounts for ~15,000 new cases per year.
- Fibromyalgia (a nociplastic condition) is diagnosed in ~2–5% of Australians, with a female-to-male ratio of approximately 3:1.
- Chronic low back pain — often mixed nociceptive/nociplastic — is the leading cause of disability in Australia (AIHW, 2023).
- Aboriginal and Torres Strait Islander Australians experience chronic pain at 1.4 times the rate of non-Indigenous Australians, with markedly lower access to multidisciplinary pain management (AIHW, 2022).
- The Australian Institute of Health and Welfare reports that opioid dispensing for chronic non-cancer pain remains high despite declining trends since 2018, underscoring the need for mechanism-based prescribing.
Nociceptive Pain
Definition & Pathophysiology
Nociceptive pain arises from the activation of peripheral nociceptors (Aδ and C fibres) by actual or threatened tissue damage. Nociceptors transduce mechanical, thermal, or chemical stimuli into electrical signals that travel via the spinothalamic tract to the thalamus and somatosensory cortex. Inflammatory mediators (prostaglandins, bradykinin, substance P, TNF-α, IL-1β) sensitise peripheral nociceptors (peripheral sensitisation), lowering activation thresholds and amplifying pain signalling.
Nociceptive pain is typically proportional to the stimulus, well-localised, and described as aching, throbbing, or sharp. It serves a protective biological function and generally resolves with tissue healing.
Clinical Subtypes
| Subtype | Examples | Characteristics |
|---|---|---|
| Somatic — superficial | Skin laceration, burn, abrasion | Sharp, well-localised, immediate onset |
| Somatic — deep | Fracture, osteoarthritis, muscle strain, post-operative wound | Aching, throbbing, worse with movement |
| Visceral | Renal colic, appendicitis, mesenteric ischaemia, endometriosis | Diffuse, poorly localised, may refer to dermatomes; nausea/vomiting common |
Diagnostic Features
- Pain consistent with identifiable tissue pathology (imaging, examination findings)
- Proportional to nociceptive stimulus
- Responsive to simple analgesics and anti-inflammatories
- No neurological deficits (unless complicated by nerve compression)
- DN4 score typically < 4/10
Pharmacological Management
Neuropathic Pain
Definition & Pathophysiology
Neuropathic pain is defined by the IASP as "pain caused by a lesion or disease of the somatosensory nervous system." It may be peripheral (affecting peripheral nerves, nerve roots, or dorsal root ganglia) or central (affecting the spinal cord or brain).
Key pathophysiological mechanisms include:
- Ectopic nerve firing: Damaged nerves generate spontaneous action potentials without peripheral stimulus, often via upregulated sodium channels (Nav1.3, Nav1.7, Nav1.8).
- Peripheral sensitisation: Increased excitability of intact nociceptors surrounding the lesion (inflammatory soup).
- Central sensitisation: Increased excitability of dorsal horn neurons (wind-up phenomenon, NMDA receptor activation), leading to allodynia and hyperalgesia.
- Loss of inhibitory interneurons: Reduced GABAergic/glycinergic tone in the dorsal horn, disinhibiting pain transmission.
- Sympathetic coupling: Sympathetic efferents may interact with damaged sensory neurons, contributing to complex regional pain syndrome (CRPS).
- Descending facilitation: Maladaptive changes in brainstem nuclei (periaqueductal grey, rostral ventromedial medulla) that normally inhibit spinal pain transmission.
Common Causes in Australian Practice
| Peripheral | Central |
|---|---|
| Diabetic peripheral neuropathy (DPN) | Spinal cord injury / compression |
| Post-herpetic neuralgia (PHN) | Post-stroke pain (thalamic) |
| Chemotherapy-induced peripheral neuropathy (CIPN) | Multiple sclerosis |
| Trigeminal neuralgia | Syringomyelia |
| Nerve entrapment (carpal tunnel, meralgia paraesthetica) | Central post-stroke pain |
| HIV-associated neuropathy | Parkinson's disease (rare) |
| Phantom limb pain |
Clinical Features
Neuropathic pain is characterised by a distinct quality and sensory profile:
- Burning, shooting, electric-shock, tingling, or "pins and needles"
- Allodynia: pain from a normally non-painful stimulus (e.g., light touch, clothing on skin)
- Hyperalgesia: exaggerated pain response to a normally painful stimulus
- Paraesthesia / dysaesthesia: spontaneous unpleasant sensations
- Often worse at night, disrupting sleep
- Distribution follows a dermatomal or peripheral nerve pattern
- Neurological examination may reveal sensory loss (pinprick, vibration, temperature) in the affected territory
Screening & Diagnostic Tools
The following validated tools assist identification of neuropathic pain components:
Pharmacological Management — First-Line Agents
The following are recommended as first-line by the Australian Pain Society, Faculty of Pain Medicine (ANZCA), and Therapeutic Guidelines. Choice depends on comorbidities, side-effect profile, and patient preference.
Second-Line & Refractory Agents
Nociplastic Pain
Definition & Pathophysiology
Nociplastic pain (IASP 2017) is "pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain." Previously termed "central sensitisation" or "functional pain," it represents a shift in pain processing rather than structural pathology.
Key mechanisms include:
- Central sensitisation: Amplified CNS processing of nociceptive signals with enhanced synaptic efficacy in dorsal horn neurons and thalamocortical networks.
- Altered descending modulation: Impaired descending inhibition (reduced noradrenergic/serotonergic activity from brainstem) and/or enhanced descending facilitation.
- Disrupted endogenous opioid function: Reduced μ-opioid receptor availability or altered endorphin/enkephalin release.
- Neuroinflammation: Glial cell activation (microglia, astrocytes) in the CNS releasing pro-inflammatory cytokines that sustain pain amplification.
- Psychoneuroimmune interactions: Stress, sleep deprivation, and psychological distress directly modulate immune and neural pain pathways.
Clinical Features — The Nociplastic Pain Phenotype
- Widespread or diffuse pain disproportionate to identifiable pathology
- Pain that does not follow a dermatomal or peripheral nerve distribution
- Tenderness to palpation in multiple body regions (not just the primary site)
- Associated symptoms: fatigue, unrefreshing sleep, cognitive difficulties ("fibro fog"), mood disturbance
- Disproportionate sensitivity to environmental stimuli (noise, light, temperature)
- Symptom flare triggered by stress, poor sleep, or weather changes
- Poor response to conventional analgesics including opioids
Prototypical Nociplastic Conditions
| Condition | Key Features | Diagnostic Criteria |
|---|---|---|
| Fibromyalgia | Widespread pain >3 months, fatigue, sleep disturbance, cognitive symptoms | ACR 2016: Widespread Pain Index (WPI) ≥7 + Symptom Severity Scale (SSS) ≥5, or WPI 3–6 + SSS ≥9 |
| Irritable bowel syndrome (IBS) | Abdominal pain related to defaecation, altered bowel habit | Rome IV criteria: recurrent abdominal pain ≥1 day/week for ≥3 months |
| Chronic pelvic pain | Pelvic pain >6 months; often co-occurs with endometriosis and bladder pain syndrome | Clinical diagnosis of exclusion after investigation |
| Temporomandibular disorder (TMD) | Jaw pain, clicking, restricted opening | DC/TMD criteria |
| Chronic tension-type headache | Bilateral pressing/tightening headache ≥15 days/month | ICHD-3 criteria |
| Non-specific chronic low back pain | Low back pain >3 months with no clear structural cause on imaging | Clinical diagnosis; imaging only if red flags present |
Pharmacological Management
Nociplastic pain responds poorly to conventional analgesics. Multimodal, primarily non-pharmacological strategies form the cornerstone, with pharmacotherapy as adjunctive.
Non-Pharmacological Interventions (Core Management)
Mixed Pain
Definition
Mixed pain is the simultaneous presence of two or more mechanistic pain types in a single clinical syndrome. It is the most common presentation in chronic pain and is frequently encountered in primary care. The IASP recognises that pain mechanisms are not mutually exclusive and many conditions involve overlapping nociceptive, neuropathic, and nociplastic components.
Common Mixed Pain Syndromes in Australian Practice
| Condition | Nociceptive Component | Neuropathic Component | Nociplastic Component |
|---|---|---|---|
| Cancer pain | Bone metastases, visceral infiltration, tumour mass effect | Nerve compression/infiltration, chemotherapy-induced neuropathy, radiation plexopathy | Central sensitisation from prolonged nociceptive input, psychosocial distress |
| Lumbar radiculopathy | Disc herniation, facet joint arthropathy, muscle spasm | Nerve root compression → dermatomal pain, paraesthesia, motor weakness | Central sensitisation if pain persists >3 months; widespread hyperalgesia |
| Diabetic neuropathic pain with Charcot foot | Fracture, joint destruction, soft tissue inflammation | Peripheral neuropathy (sensory loss, burning pain) | Altered central processing |
| Post-surgical chronic pain | Ongoing tissue inflammation, mesh-related (hernia repair) | Nerve entrapment (ilioinguinal, intercostal neuroma) | Central sensitisation, pre-existing psychological vulnerability |
| Chronic knee osteoarthritis | Cartilage loss, subchondral bone oedema, synovitis | Peripheral nerve sensitisation (small-fibre pathology demonstrated in OA) | Central sensitisation, widespread hyperalgesia, catastrophising |
| Endometriosis-related pain | Peritoneal implants, adhesions, cyclical inflammation | Nerve infiltration by endometriotic lesions (sciatic, pudendal) | Central sensitisation with persistent symptoms despite hormonal suppression |
Clinical Approach to Mixed Pain
Cancer Pain — A Mixed Pain Paradigm
Cancer pain exemplifies mixed pain and requires a WHO analgesic ladder–based approach modified by mechanism:
| WHO Ladder Step | Nociceptive Component | Neuropathic Component |
|---|---|---|
| Step 1 — Mild pain (NRS 1–3) | Paracetamol ± NSAID | Add adjuvant (amitriptyline, gabapentin, duloxetine) |
| Step 2 — Moderate pain (NRS 4–6) | Add weak opioid (tramadol, codeine) or low-dose strong opioid | Escalate adjuvant; consider corticosteroid for nerve compression |
| Step 3 — Severe pain (NRS 7–10) | Strong opioid (morphine, oxycodone, fentanyl) + adjuvants | High-dose adjuvant ± ketamine (specialist), nerve block, radiation therapy |
Pathophysiology — Integrative Overview
Understanding the nociceptive pathway from periphery to cortex clarifies where each pain mechanism disrupts normal processing:
Biomarkers & Emerging Diagnostics
- Conditioned pain modulation (CPM): Quantitative sensory testing (QST) paradigm measuring endogenous analgesia; reduced CPM predicts nociplastic phenotype and poor opioid response. Available at some Australian research pain centres (not routine clinical practice).
- Functional MRI (fMRI): Demonstrates altered brain connectivity (default mode network, salience network) in nociplastic pain; research tool only.
- Genetic polymorphisms: COMT, SCN9A, OPRM1 variants influence pain sensitivity and analgesic response; not yet clinically validated for routine use in Australia.
Investigations
Investigations in pain assessment should be guided by the suspected mechanism and should always include screening for underlying causes and treatable contributors.
Special Populations
Pregnancy
Paediatrics
Elderly (≥65 years)
Renal Impairment
Hepatic Impairment
Immunocompromised
Aboriginal and Torres Strait Islander Health Considerations
Chronic pain is a significant and under-recognised health burden for Aboriginal and Torres Strait Islander Australians. The 2018–19 National Aboriginal and Torres Strait Islander Health Survey found that 27% of Indigenous Australians reported chronic pain, compared with 19% of non-Indigenous Australians — a 1.4-fold excess burden. Despite this higher prevalence, access to specialist pain management, allied health services, and culturally appropriate care is markedly lower, particularly in remote and very remote communities.
Key Factors Contributing to Pain Burden
Culturally Safe Pain Management Strategies
- Aboriginal Health Workers/Practitioners (AHW/AHP): Engage AHW/AHP as key members of the pain management team. They provide culturally safe education, facilitate communication, support medication adherence, and act as a bridge between Western biomedical and Indigenous health frameworks. Funded under MBS item 715 (health check) and 721 (GP Management Plan).
- Yarning-based pain assessment: Use conversational, narrative-based assessment ("Can you tell me about your pain?") rather than formal questionnaires. Explore impact on cultural activities, community obligations, and connection to Country.
- Telehealth pain management: The Australian Government's telehealth MBS items (video consultation items 99200–99215) enable specialist pain consultations in remote communities. Several state pain services (e.g., NSW Agency for Clinical Innovation Pain Management Network, SA Pain Management Network) offer rural/remote telehealth pathways.
- Community-based models: The Central Australian Rural Practitioners Association (CARPA) Standard Treatment Manual provides culturally adapted pain guidelines for remote NT. The Lowitja Institute supports Indigenous health research including chronic pain.
- Addressing yellow flags within a cultural context: Fear-avoidance, catastrophising, and social withdrawal may manifest differently. Koori/Aboriginal community-controlled health organisations (ACCHOs) can provide integrated pain and social-emotional wellbeing support.
- Medication access in remote communities: Remote Area Aboriginal Health Services (RAAHS) stock essential analgesics including paracetamol, amitriptyline, gabapentin, and tramadol. Pregabalin and duloxetine (authority-required) may face delays; pre-approval through PBS authority phone line (1800 888 333) can facilitate timely access.
- Close the Gap — pain management equity: Pain management should be embedded in chronic disease management strategies aligned with the National Agreement on Closing the Gap (2020), particularly Priority Reform 1 (formal partnerships) and Priority Reform 2 (community-controlled sector building).
📚 References
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