Chronic Pain: Definition, Classification, and Management
Introduction
Chronic pain is a complex condition that persists beyond normal tissue healing time and significantly impacts quality of life. Unlike acute pain, which serves a protective function, chronic pain is often maladaptive and can lead to disability, psychological distress, and social consequences.
Definition of Chronic Pain
According to the International Association for the Study of Pain (IASP), chronic pain is defined as:
“Pain that persists or recurs for more than 3 months and may or may not be associated with an identifiable cause.”
Classification of Chronic Pain
1. Based on Pathophysiology
• Nociceptive Pain: Due to activation of nociceptors by tissue damage or inflammation.Example: Osteoarthritis, cancer pain.
• Neuropathic Pain: Due to nerve damage or dysfunction. Example: Diabetic neuropathy, post-herpetic neuralgia.
• Nociplastic Pain: Pain without clear nociceptive or neuropathic origin, often due to central sensitization.,Example: Fibromyalgia, chronic low back pain.
2. Based on Duration and Course
• Recurrent Pain: Pain that occurs intermittently over months/years (e.g., migraine).
• Persistent Pain: Continuous pain lasting beyond expected healing (e.g., failed back surgery syndrome).
• Progressive Pain: Pain that worsens over time (e.g., cancer pain).
3. Based on Etiology
• Primary Chronic Pain: No clear underlying cause (e.g., fibromyalgia, chronic migraine).
• Secondary Chronic Pain: Caused by identifiable pathology (e.g., rheumatoid arthritis, post-surgical pain).
Mechanisms of Chronic Pain
Peripheral Mechanisms
1. Peripheral Sensitization: Increased responsiveness of nociceptors to stimuli.
2. Ectopic Discharges: Abnormal spontaneous nerve activity after injury.
Central Mechanisms
1. Central Sensitization: Hyperexcitability of spinal neurons, leading to exaggerated pain responses.
2. Disinhibition: Loss of endogenous pain inhibition.
3. Neuroplasticity: Rewiring of pain pathways, contributing to persistent pain.
Assessment of Chronic Pain
Pain Scales
• Numerical Rating Scale (NRS): 0–10 scale.
• Visual Analog Scale (VAS): 10 cm line, patient marks pain intensity.
• McGill Pain Questionnaire: Assesses sensory, affective, and evaluative aspects of pain.
Functional and Psychological Assessment
• Brief Pain Inventory (BPI): Measures pain interference in daily life.
• Hospital Anxiety and Depression Scale (HADS): Evaluates psychological impact.
• Neuropathic Pain Questionnaire (DN4, LANSS): Identifies neuropathic pain features.
Management of Chronic Pain
1. Pharmacological Management
A. Non-Opioid Analgesics
• Paracetamol: First-line for mild pain (Max dose: 4g/day).
• NSAIDs (Ibuprofen, Naproxen, Celecoxib): Useful for inflammatory pain but have GI and renal side effects.
B. Neuropathic Pain Medications
• Antidepressants (TCAs, SNRIs):
• Amitriptyline: 10–25 mg HS, increases serotonin & norepinephrine.
• Duloxetine: 30–60 mg/day, used for diabetic neuropathy.
• Anticonvulsants (Gabapentinoids):
• Gabapentin: 300–3600 mg/day, reduces nerve excitability.
- Pregabalin: 75–300 mg/day, preferred for neuropathic pain.
C. Opioids (Reserved for Severe Pain)
• Used in cancer pain or refractory cases.
• Examples: Tramadol (50–100 mg Q6H), Morphine, Fentanyl patches.
• Side Effects: Tolerance, dependence, respiratory depression.
D. NMDA Antagonists
• Ketamine (Oral/IV/Topical): Blocks central sensitization.
• Memantine: Used in fibromyalgia and CRPS.
E. Topical Agents
• Lidocaine 5% Patch: For post-herpetic neuralgia.
• Capsaicin Cream: Depletes substance P, used in neuropathic pain.
2. Interventional Pain Management
A. Nerve Blocks
• Peripheral Nerve Blocks: Sciatic, femoral, brachial plexus blocks.
• Sympathetic Blocks: Stellate ganglion block for CRPS, celiac plexus block for pancreatic cancer pain.
B. Epidural and Spinal Injections
• Epidural Steroid Injection (ESI): For radicular pain and spinal stenosis.
• Intrathecal Opioids: Morphine, Baclofen pumps for refractory pain.
C. Radiofrequency Ablation (RFA)
• Used for facet joint pain, trigeminal neuralgia.
D. Neuromodulation Techniques
• Spinal Cord Stimulation (SCS): Electrodes implanted in epidural space, used for failed back surgery syndrome.
• Peripheral Nerve Stimulation (PNS): Stimulates specific nerves to reduce pain.
3. Psychological and Behavioral Therapy
• Cognitive Behavioral Therapy (CBT): Reduces pain perception and distress.
• Mindfulness-Based Stress Reduction (MBSR): Improves coping mechanisms.
• Biofeedback Therapy: Helps control physiological responses to pain.
4. Physical Therapy and Rehabilitation
• TENS (Transcutaneous Electrical Nerve Stimulation): Reduces pain signals via gate control mechanism.
• Physiotherapy: Strengthens muscles, improves function.
• Acupuncture: Stimulates endogenous opioid release.
5. Complementary and Alternative Medicine (CAM)
• Herbal Medicine: Turmeric, Boswellia for anti-inflammatory effects.
• Yoga and Tai Chi: Improve flexibility, reduce pain perception.
Complications of Untreated Chronic Pain
1. Physiological: Hypertension, tachycardia, immune suppression.
2. Psychological: Depression, anxiety, sleep disorders.
3. Social: Loss of productivity, financial burden.
4. Opioid Dependence: Due to inadequate pain management.
MCQs
1. Which of the following is NOT a neuropathic pain condition?
a) Post-herpetic neuralgia
b) Diabetic neuropathy
c) Rheumatoid arthritis
d) Complex regional pain syndrome
Answer: c) Rheumatoid arthritis
2. Which neurotransmitter is involved in central sensitization?
a) Dopamine
b) Serotonin
c) Glutamate
d) Acetylcholine
Answer: c) Glutamate
3. Which medication is a first-line treatment for neuropathic pain?
a) Ibuprofen
b) Paracetamol
c) Gabapentin
d) Aspirin
Answer: c) Gabapentin
4. Which nerve block is used for complex regional pain syndrome (CRPS)?
a) Stellate ganglion block
b) Brachial plexus block
c) Sciatic nerve block
d) Intercostal nerve block
Answer: a) Stellate ganglion block
5. Which of the following is a side effect of prolonged opioid use?
a) Hyperalgesia
b) Bradycardia
c) Hypoglycemia
d) Hyperkalemia
Answer: a) Hyperalgesia
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