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