Chronic pain

Introduction

• Definition:
  • Pain >3 months
  • Pain persisting beyond reasonable time for injury to heal
  • Pain >1 month beyond usual course of an acute disease
• Serves no biological function, is not an indication of ongoing tissue damage and complete pain relief is unrealistic
• Goal of therapy is pain management and return to functional status
• Prevalence
  • 30% of the population
  • Women (34%) > men (27%)
  • Back > knee > neck
  • Neuropathic pain affects 6.9-10% of the population
• Psychosocial aspects
  • Associated depression
  • Drug diversion for income
  • Dependent personality
• Allodynia common
• There is little evidence for long-term opioid use
  • No clinical trial for effects >1 year
  • Some evidence that chronic use worsens pain perception
  • Reasonable evidence that opioids provide no benefit in chronic back pain or joint pain
  • Focuses attention on pharmacological management vs. behavioural/psychological
• Risk factors
  • Increased age
  • Female gender
  • Increased body weight
  • Chronic illness
• Exacerbation of chronic pain = 11-15% of ED visits

Pathophysiology

• Initial tissue injury, with nerve dysfunction due to chemical mediator release or mechanical nerve injury
• Peripheral nerves and/or CNS abnormally sensitive through upregulation of sodium channels and receptors
• Neuroplastic changes in central descending pain modulatory systems leads to further hyperexcitability
• Hyperalgesia (exaggerated response to a normally painful stimulus)
• Allodynia (pain from a normally non-painful stimulus)
• Psychological factors may occur prior to or with chronic pain, leading to fear-avoidance model physiological changes leading to disuse disability and further nerve hyperexcitability and dysfunction

Clinical features

• History
  • Pain history, exacerbating, relieving
  • Prior episodes and outcomes
  • Previous treatments and outcomes
  • Medication history/dependence/addiction
  • Functional status
  • ROS for potential limb- or life-threatening diagnoses
• Examination
  • No observed correlation between vital signs and numeric pain scores for ED patients
  • Muscle atrophy, skin temperature changes suggest chronic pain syndrome
  • Trigger points – Result in referred pain throughout the affected muscle and remain an essential feature of myofascial pain syndromes

Non-neuropathic pain syndromes

• Myofascial headache
  • Constant dull pain, with occasional shooting pain. Triggers points on scalp, muscle tenderness and tension
• Chronic tension headache
  • Chronic dull pain with diffuse scalp tenderness and associated tension
• Transformed migraine
  • Migraine-like becoming constant and dull with nausea/vomiting
  • Muscle tenderness and tension with normal neuro exam
• Myofascial neck pain
  • Constant dull pain with occasional shooting pain; does not follow nerve distribution. Triggers points with no muscle atrophy. Poor ROM in involved muscle.
• Chronic neck pain
  • Constant dull pain with occasional shootinpain. Does not follow nerve distribution. No trigger points. Poor ROM in involved muscle.
• Chronic back pain
  • Constant dull pain with occasional shooting pain. Does not follow nerve distribution. No trigger points. Poor ROM in involved muscle.
• Myofascial back pain syndrome
  • Constant dull pain with occasional shooting pain. Does not follow nerve distribution. Trigger points with no muscle atrophy. 

Neuropathic pain syndromes

• Painful diabetic neuropathy
  • Symmetric numbness and burning pain in lower extremities; allodynia may occur
  • Sensory loss in lower extremities
• Phantom limb pain (30-80% of amputations)
• Trigeminal neuralgia
  • Paroxysmal, short bursts of severe pain in nerve distribution. Tearing or red eye may occur
  • Pain may be triggered by brushing teeth, chewing, speaking, touching face
• Post-herpetic neuralgia (5-30% of cases lasting >1 year for 30%)
  • Allodynia, shotting, lancinating pain. Sensory changes in involved dermatome
• Fibromyalgia (5.4% of population)
  • Widespread muscular pain and stiffness, fatigue, sleep disturbance and cognitive dysfunction. Muscle tenderness in >6 body areas out of 19 total regions
• Post-stroke pain
  • Same side as weakness; throbbing, shooting, allodynia. Loss of hot/cold differentiation
• Sciatica
  • Constant or intermittent, burning or aching, shooting or electric-shock, may follow dermatome. Leg > back pain. Possible muscle atrophy in area of pain +- possible reflex changes

Transformed migraine

• Classic or common migraine changes into chronic pain syndrome, usually due to medication overuse
• Chronic migraine (15 or more migraine days per month) is a precursor to transformed migraine
• Barbiturates >5 days per month; opioids >8 days per month and triptans/NSAID’s >10 days per month
• Headache duration is longer, nausea/vomiting often prominent and tenderness/tension of scalp musculature is common

Complex regional pain syndrome

• Type I
  • From prolonged immobilisation or disuse
  • Burning persistent pain, allodynia, not associated with nerve injury
  • Early: Oedema, warmth, local sweating
  • Late: Above alternating with cold, pale, cyanosis and atrophy
• Type II
  • Associated with peripheral nerve injury
  • Burning persistent pain, allodynia
  • Early: Oedema, warmth, local sweating
  • Late: Above alternating with cold, pale, cyanosis and atrophy
  • Usually more painful and difficult to control

Diagnosis

• Ensure not missing alternative diagnosis
• Focused management
  • Identify exacerbation of chronic pain
  • Appropriate rescue pain relief
  • Reinforce need for single practitioner

Treatment

• Opioids for chronic pain
  • For back pain only if more severe or refractory to non-opioid analgesics
  • Lowest practical dose for limited duration and consider risk s of misuse, abuse or diversion
  • Avoid routine prescribing of opioids for acute exacerbations of chronic non-cancer pain seen in ED
  • Honor existing patient-physician contracts
  • Consider past prescription patterns
  • IV or IM opioids in ED for acute exacerbations of chronic pain is discouraged
  • Do not provide replacement prescriptions for lost, destroyed or stolen controlled substances
  • Long-acting or controlled-release opioids should not be prescribed from ED
  • Do not provide replacement doses of methadone for patients on program
  • If opioids are prescribed, provide only enough pills to last until primary carer opens
• Chronic non-neuropathic pain syndromes
  • Myofascial pain
    • NSAID’s, topical dislofenac for single site
    • Amitryptiline second-line
    • Referral for trigger point injections, dry needling, US treatment, optimisation of therapy and exercise
  • Chronic migraine
    • Treat as for exacerbation of episodic migraine
    • Consider prophylaxis with sodium valproate or topiramate
    • Referral for optimisation of medical therapy
  • Transformed migraine/medication overuse headache
    • Stop prior medications
    • Celecoxib or prednisone taper during withdrawal period
    • Referral for optimisation and consideration of prophylactic agents
• Chronic neuropathic pain syndromes
  • Fibromyalgia
    • 1^st Pregabalin – 2^nd Duloxetine
  • Trigeminal neuralgia
    • Carbamazepine – Oxcarbazine
  • HIV neuropathy pain
    • Capsaicin – Gabapentin
  • Spinal cord pain
    • Pregabalin – Tramadol
  • Painful diabetic neuropathy
    • Duloxetine – Gabapentin/pregabalin
  • Post-herpetic neuralgia
    • Gabapentin/pregabalin – Tramadol
  • Phantom limb pain
    • Gabapentin – Tramadol
  • Post-stroke pain
    • Pregabalin – Gabapentin
  • Complex regional pain syndrome
    • Prednisone in acute phase – Intermittent low-dose ketamine infusions for late phase
• Tramadol is second-line as not as effective as primary treatments
• IV ketamine infusions for complex regional pain syndrome improve pain but do not improve function
• Steroids do not alter the course of complex regional pain syndrome but are recommended when inflammation is present in acute phase
• Cyclic antidepressants are second-line and useful for most neuropathic pain syndromes, with the exception of spinal cord injury pain, phantom limb pain, HIV related neuropathy and chronic regional pain syndrome

In the elderly

• NSAID’s have risks but less risk of premature death and overall side effects than opioids in the elderly
• GI bleeding rates are similar for patients treated with opioids or non-selective NSAID’s
• Topical NSAID’s are an excellent choice
• Look for non-verbal signs of pain in cognitively impaired elderly patients and treat accordingly

Aberrant drug-related behaviour

• The only consistent predictor of aberrant drug-related behaviour in chronic pain patients is a personal history of illicit drug or alcohol abuse
• Most common complaints are:
  • Back pain > headache > extremity pain > dental pain
• Examination
  • Physical signs of pain
  • Signs of IV drug use
  • Regurgitant murmur suggestive of prior IE
  • Allergy to many analgesics
  • Aberrant behaviours: Forges/alters prescriptions, sells controlled drugs, uses aliases, current illicit drug use, factitious illness, conceals multiple prescribers, abusive when refused, conceals multiple ED visits
• Review prescription drug monitoring programs

Last Updated on August 29, 2024 by Andrew Crofton