Chronic pain Sai Yan Au
Chronic Pain Definition Causes and mechanisms of chronic pain Effects of chronic pain Assessment and evaluation Management
Definition Pain which persists a month beyond the usual course of an acute disease or reasonable time for an injury to heal Pain that recurs at intervals for months or years Different in definitions – important for an effective therapy
Causes and mechanisms Causes –Chronic pathologic processes in somatic structures or viscera –Prolonged or permanent dysfunction of the PNS or CNS –Psychological mechanisms or environmental factors
Mechanisms of chronic pain More complex than acute pain 3 types: - Peripheral mechanisms Peripheral – central mechanisms Central mechanisms Psychological and environmental mechanisms
Peripheral mechanisms Likely for chronic pain assoc. with chronic MSK, visceral and vascular disorders May be due to noxious stimulation of nociceptors or their sensitization May be initiated by these factors and prolonged by their persistence, by various reflex mechanism and by other factors Chronic pain can be produced by pathology limited to peripheral nerves
Peripheral – central mechanisms Probably operated on chronic pain syndromes assoc. with partial or complete lesions of the peripheral nerves, dorsal roots or dorsal ganglion cells Produce serious and prolonged dysfunction Probably occur in causalgia and other reflex sympathetic dystrophy, phantom limb pain, in postherpetic neuralgia, in cancer pain,
Central mechanisms Disease or injury to the CNS Characterized by spontaneous burning or aching pain, hyperalgesia, dysesthesia, hyperpathia and other abnormal sensation Sometimes accompanies thalamic lesions, accidental injury to spinal cord and surgical interruption which affects the pain pathways
Effects of chronic pain Depends on the:- Cause or mechanisms The genetic makeup Variety of sociologic factors
Physiologic and behavioural effects Mental and psychologic effects of chronic pain and suffering Sociologic effects
Assessment Medical approach Psychological evaluation Behavioural based treatment Clinical examination Special attention whether patient guard the painful area Whether certain movements or postures are avoided because of pain
Management Identify specific and realistic functional goals Counseling, physical therapy, nerve blocks or even surgery to improve patient’s QOL Referral to pain clinic
Pharmacological management Antidepressant medications TCAs Value in treatment of neuropathic pains e.g. diabetic neuropathy and postherpetic neuralgia
Anticonvulsants and antiarrhythmics Phenytoin and carbamazepine relieve pain of trigeminal neuralgia Lidocaine also effective for neuropathic pain
Chronic opioid medication Explain to patient the limitations and risks of opioid Long acting compounds (methadone or levorphanol) for long term outpatient use Morphine Aspirin NSAIDS