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 mechanismsPeripheral – central mechanismsCentral mechanismsPsychological 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 mechanismsThe genetic makeupVariety 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 examinationSpecial attention whether patient guard the

painful areaWhether 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 medicationsTCAsValue in treatment of neuropathic pains e.g.

diabetic neuropathy and postherpetic neuralgia

Anticonvulsants and antiarrhythmicsPhenytoin and carbamazepine relieve pain

of trigeminal neuralgiaLidocaine also effective for neuropathic

pain

Chronic opioid medicationExplain to patient the limitations and risks

of opioidLong acting compounds (methadone or

levorphanol) for long term outpatient useMorphineAspirinNSAIDS