Key Facts

Chronic pain is a major public health issue causing significant disability, mental health comorbidity, and healthcare utilisation. It is now recognised as a disease in its own right (ICD-11). Management has shifted from a biomedical to a biopsychosocial model emphasising self-management and functional rehabilitation.

Epidemiology

Chronic pain affects approximately 28 million adults in the UK (~43% of the population). It accounts for 4.6 million GP appointments annually. Chronic pain is the leading cause of disability worldwide. The economic cost to the UK is estimated at £12 billion annually in healthcare and lost productivity.

Aetiology

ICD-11 classification:

• Chronic primary pain: No identifiable underlying condition (fibromyalgia, chronic widespread pain, chronic primary headache)
• Chronic secondary pain: Associated with an underlying condition — musculoskeletal, neuropathic, cancer, post-surgical, visceral

Risk factors for chronification: Psychological distress, catastrophising, fear-avoidance beliefs, social isolation, previous chronic pain, adverse childhood experiences, litigation/compensation

Pathophysiology

Chronic pain involves:

• Peripheral sensitisation: Ongoing inflammatory mediator release lowering nociceptor thresholds
• Central sensitisation: Wind-up, NMDA receptor activation, microglial activation in spinal cord
• Descending modulation dysfunction: Impaired inhibitory pathways (serotonergic, noradrenergic)
• Neuroplastic changes: Cortical reorganisation, grey matter changes visible on fMRI
• Psychosocial amplification: Depression, anxiety, catastrophising amplify pain experience and disability

Common Chronic Pain Conditions

• Chronic low back pain: Most common cause of chronic pain in the UK
• Fibromyalgia: Widespread pain, fatigue, cognitive dysfunction, sleep disturbance
• Complex regional pain syndrome (CRPS): Burning pain, allodynia, vasomotor changes, trophic changes
• Neuropathic pain: Post-herpetic neuralgia, diabetic neuropathy, trigeminal neuralgia
• Chronic post-surgical pain: After thoracotomy (30-50%), mastectomy (20-50%), hernia repair (10-30%)

Assessment

• Pain history: Location, character, severity, temporal pattern, aggravating/relieving factors
• Functional impact: Activities of daily living, work, sleep, relationships
• Psychological assessment: Depression (PHQ-9), anxiety (GAD-7), pain catastrophising scale
• Previous treatments and responses

Red Flags

• New neurological deficit with chronic back pain — cauda equina, cord compression
• Weight loss with chronic pain — consider malignancy
• Pain with systemic features (fever, night sweats) — consider infection, malignancy
• Escalating opioid requirements — consider opioid-induced hyperalgesia or dependence

Bedside

• Pain assessment tools: NRS, Brief Pain Inventory, DN4 (neuropathic pain screening)
• Psychological screening: PHQ-9 (depression), GAD-7 (anxiety)
• Functional assessment: Pain Disability Index, EQ-5D

Bloods

• FBC, ESR, CRP: Exclude inflammatory cause
• TFTs, calcium, vitamin D: Exclude metabolic causes of widespread pain
• HbA1c: If diabetic neuropathy suspected
• Myeloma screen: If bony pain in elderly

Imaging

• MRI: If red flags present — spinal pathology, tumour, infection
• X-ray: Chronic musculoskeletal pain with structural concern
• Not recommended routinely: Imaging findings often incidental and do not correlate with pain severity

Special Tests

• Nerve conduction studies/EMG: If neuropathy suspected
• Quantitative sensory testing: Specialist pain centres — characterise neuropathic pain
• Diagnostic nerve blocks: Identify pain generator (facet joints, sacroiliac joint, peripheral nerves)

Non-pharmacological

• Exercise: Graded activity, physiotherapy-led programmes — strongest evidence base
• Cognitive Behavioural Therapy (CBT): NICE recommends for all chronic pain (NG193)
• Acceptance and Commitment Therapy (ACT): Emerging evidence, focuses on values-based living
• Pain Management Programmes: Multidisciplinary rehabilitation (physiotherapy + psychology + OT)
• Mindfulness-based stress reduction (MBSR): Moderate evidence for chronic pain
• Self-management strategies: Pacing, goal-setting, sleep hygiene

Pharmacological

Chronic primary pain (NICE NG193):

• Do NOT start opioids, paracetamol, NSAIDs, gabapentinoids, benzodiazepines, or antidepressants for pain
• Consider: Antidepressant (amitriptyline/duloxetine) for associated mood symptoms

Chronic secondary pain with neuropathic component (NICE CG173):

• First-line: Amitriptyline 10-75mg ON, OR duloxetine 60-120mg OD, OR gabapentin 300-1200mg TDS, OR pregabalin 75-300mg BD
• Combination therapy: If monotherapy insufficient
• Topical: Capsaicin 0.075% QDS, lidocaine 5% patch (localised neuropathic pain)

Opioids in chronic non-cancer pain:

• Only if other options exhausted, clear goals set, regular review
• Avoid >120mg morphine equivalent daily dose
• Plan tapering and discontinuation

Surgical/Interventional

• Spinal cord stimulation: NICE TA159 — CRPS, failed back surgery syndrome
• Radiofrequency denervation: Facet joint pain, sacroiliac joint pain
• Intrathecal drug delivery: Severe cancer pain, selected chronic pain
• Nerve blocks: Diagnostic and short-term therapeutic
• Neuromodulation: Dorsal root ganglion stimulation, peripheral nerve stimulation

Referral Criteria

• Chronic pain affecting function and quality of life — refer to pain management service
• Complex chronic pain with psychological comorbidity — multidisciplinary pain management programme
• Neuropathic pain refractory to first-line agents — specialist pain clinic
• Consider spinal cord stimulation — if CRPS or FBSS meets NICE criteria

• Complete pain resolution is uncommon in chronic primary pain — management focuses on function and quality of life
• Pain management programmes: 50-70% of patients show clinically significant improvements in function and mood
• Neuropathic pain: ~50% achieve ≥50% pain reduction with optimised medication
• Spinal cord stimulation: ~60% achieve >50% pain relief for CRPS; cost-effective at 5 years
• Opioid tapering: Many patients report improved pain and function after opioid reduction (POINT study)
• Long-term opioids: Associated with increased mortality, endocrine dysfunction, immune suppression, and hyperalgesia

NICE NG193 Key Recommendations for Chronic Primary Pain

Budapest Criteria for CRPS

Diagnosis requires: ≥1 symptom in 3/4 categories AND ≥1 sign in 2/4 categories at examination.

Opioid Conversion Table (Oral Morphine Equivalents)