Understanding Pain

Dr Yeo Sow NamDirector, The Pain Specialist,

Mount Elizabeth Hospital &Founder and Past Director,

Pain Management and Acupuncture Services, Singapore General Hospital

MBBS (Singapore)MMED (Anesthesiology, S’pore)

FANZCA (Anesthesiology, Aust/NZ)FFPMANZCA (Pain Medicine, Aust/NZ)

FAMS, Registered Acupuncturist 1

Sections

1. What Is Pain?2. Classification Of Pain3. What Is Neuropathic Pain?4. Summary

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What Is Pain?

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“An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”

Merskey H, et al. (Eds) In: Classification of Chronic Pain: Descriptions of Chronic Pain Syndromes and Definitions of Pain Terms. 1994:209-212.

International Association for the Study of Pain (IASP), 1994

Classifications Of Pain

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Duration

Pathophysiology

Acute Chronic

Nociceptive Neuropathic

The Continuum Of Pain

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<1 month

Time to resolution

3-6 months

AcutePain

ChronicPain

• Usually obvious tissue damage• Increased nervous system activity• Pain resolves upon healing• Serves a protective function

• Pain for 3–6 months or more2

• Pain beyond expected period of healing2

• Usually has no protective function3

• Degrades health and function3

1. Cole BE. Hosp Physician 2002;38:23-30;2. Turk and Okifuji. Bonica’s Management of Pain. 2001;3. Chapman and Stillman. Pain and Touch. 1996.

Insult

IASP Definitions: Peripheral Neuropathic and Central Neuropathic Pain

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Neuropathic painPain initiated or caused by a primary

lesion or dysfunction in the nervous system

Peripheral neuropathic painPain initiated or caused by a primary

lesion or dysfunction in the peripheral nervous system

Central neuropathic painPain initiated or caused by a primary

lesion or dysfunction in the central nervous system

Merskey H, et al. (Eds) In: Classification of Chronic Pain: Descriptions of Chronic Pain Syndromes and Definitions of Pain Terms. 1994:209-212.

Neuropathic Pain: A Redefinition

7Treede R-D, et al. Neurology 2008;70:1630-1635.

Pain arising as a direct consequence of a lesion or disease affecting the somatosensory system.

Examples• Postherpetic neuralgia• Trigeminal neuralgia• Painful diabetic neuropathy• Postsurgical neuropathic pain• Posttraumatic neuropathy• Central poststroke pain

Common descriptors2

• Burning• Tingling• Hypersensitivity to touch or cold

Examples• Pain due to inflammation• Limb pain after a fracture• Joint pain in osteoarthritis• Postoperative visceral pain Common descriptors2

• Aching• Sharp• Throbbing

Examples• Low back pain with

radiculopathy• Cervical

radiculopathy• Cancer pain• Carpal tunnel

syndrome

Mixed PainPain with

neuropathic and nociceptive components

Neuropathic PainPain initiated or caused by a primary lesion or dysfunction

in the nervous system (either peripheral or

central nervous system)1

Nociceptive PainPain caused by injury to

body tissues (musculoskeletal,

cutaneous or visceral)2

Presentation Across Pain States Varies

1. International Association for the Study of Pain. IASP Pain Terminology;2. Raja et al. in Wall PD, Melzack R (Eds). Textbook of Pain. 4th Ed. 1999;11-57.

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Development Of Neuropathic Pain

9Woolf CJ, Mannion RJ. Lancet 1999;353:1959-64.

Neuropathic painSpontaneous pain Stimulus-evoked pain

Mechanisms

Metabolic Traumatic

ToxicIschemic

Hereditary

Compression

Infectious

Immune-related

Syndrome

Symptoms

Pathophysiology

Etiology

Nerve damage

Signs And Symptoms Of Neuropathic Pain

Spontaneous symptoms

• Spontaneous pain1 Persistent burning, intermittent shock-like or lancinating pain

• Dysesthesias2 Abnormal unpleasant sensations, eg, shooting, lancinating, burning

• Paresthesias2 Abnormal, not unpleasant sensations, eg, tingling

Stimulus-evoked symptoms

• Allodynia2 Painful response to a non-painful stimulus, eg, warmth, pressure, stroking

• Hyperalgesia2 Heightened response to painful stimulus, eg, pinprick, cold, heat

• Hyperpathia2 Delayed, explosive response to any painful stimulus

1.Baron R. Clin J Pain 2000;16:S12-S20;2. Merskey H et al. (Eds) In: Classification of Chronic Pain: Descriptions of Chronic Pain Syndromes and Definitions of Pain Terms. 1994:209-212. 10

Summary• An unpleasant sensory and emotional

experience associated with actual or potential tissue damage, or described in terms of such damage

• The two most frequently used approaches for classifying pain are based on pain duration (i.e. acute vs chronic pain) and underlying pathophysiology (i.e. nociceptive vs. neuropathic pain)

• Acute and chronic pain are often classified along a pain continuum

• Neuropathic pain is defined as pain arising as a direct consequence of a lesion or disease affecting the somatosensory system.

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