Definitions

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A

Acute (Nociceptive) Pain
Pain that follows injury to the body and generally disappears when the bodily injury heals.

Addiction
A chronic, neurologic and biologic disease; characterized by behaviors including one or more of the following: impaired control over drug use, compulsory use, continued use despite harm, and craving.  Continued craving for an opioid and the need to use the opioid for effects other than pain relief.   Physical dependence and tolerance are not the same as addiction.

Allodynia 
Sensation of pain from a stimulus that normally does not produce pain, e.g., light touch.  Commonly seen with neuropathic pain.

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B

Breakthrough Pain
A transitory increase in pain that occurs on a background of otherwise controlled, persistent pain.

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C

Cancer Pain 
Acute, chronic or intermittent pain usually related to the disease itself (e.g., tumor invasion of tissue, compression of bodily structures) or treatment/procedures. 

Central Disinhibition 
A central mechanism of neuropathic pain; occurs when inhibitory mechanisms along the descending, modulatory pathways are either lost or suppressed, leading to abnormal excitability of central neurons.

Central Pain 
Pain initiated or caused by a primary lesion or dysfunction in the central nervous system.

Central Sensitization 
A key central mechanism of neuropathic pain; the abnormal hyperexcitability of central neurons in the spinal cord.

Chronic (Nonmalignant) Persistent Pain  
Pain that persists beyond the usual course of an acute injury or disease.

Comfort-Function (Pain) Goal 
A pain intensity rating identified by a patient above which the patient experiences interference with function and quality of life, e.g., activities the patients wants or needs to perform.

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D

Dorsal Horn
The inner, butterfly shaped gray matter of the spinal cord, which is the “processing center” for incoming information, including the modulation of nociceptive input

Dorsal Root Ganglia
The area in the spinal cord where nociceptive fibers have their cell bodies.

Dysesthesia
An unpleasant abnormal sensation that can be either spontaneous or evoked.

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E

Endogenous Opioids
Families of peptides (e.g., enkephalins, endorphins) that are secreted naturally by the body, and are capable of producing effects similar to exogenous opioids (e.g., inhibiting pain transmission)

Exogenous Opioids
Drugs derived from opium that are administered to produce analgesia (e.g., morphine, codeine)

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H

Hyperalgesia
An increased response to a stimulus which is normally painful; decreased sensitivity to pain.

Hypoalgesia
Diminished pain in response to a normally painful stimulus.

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M

Modulation
The activation of descending pathways that exerts inhibitory effects on the cells responsible for pain transmission

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N

Narcotic (see Opioid)
An obsolete term often used to describe ‘opioid’ analgesics; legally, controlled substances classified as ‘narcotics’ include opioids, cocaine and various other substances of potential abuse.  

Neuralgia
Pain in the distribution of a nerve or nerves; often felt as an electrical shock-like pain.

Neuritis
Inflammation of a nerve or nerves.

Neurogenic Pain
Pain initiated or caused by a primary lesion, dysfunction, or transitory perturbation in the peripheral or central nervous system.

Neuropathic (Pathophysiologic) Pain
Pain initiated or caused by a primary lesion or dysfunction in the nervous system.

Neuroplasticity
The unique ability of neurons to change their structure and function when injured.

Nociception
The perception of a potentially tissue-damaging stimulus;   It is also the term used to describe normal pain transmission

Nociceptive Pain
The normal processing of painful stimuli that causes damage to normal tissue

Nociceptor
A receptor that is preferentially sensitive to noxious stimuli or a stimulus that would be noxious if prolonged; also known as a primary afferent (carrying information to the central nervous system) neuron

Noxious Stimulus
A stimulus is one which is damaging to normal tissues.

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O

Opioid
Term preferred over ‘narcotic’; opioids include natural, semi-synthetic and synthetic drugs that relieve pain by binding to opioid receptors.

Opioid-Naïve
An opioid naïve person is one who has not recently taken enough opioid on a regular enough basis to develop tolerance to opioid induced side effects (e.g., sedation, nausea).

Opioid-Tolerant
An opioid-tolerant person is one who has taken opioids long enough at doses high enough to develop tolerance to opioid induced side effects

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P

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

• The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment. 

Pain Threshold
The least experience of pain which a subject can recognize; it is the subjective experience of the individual.

Pain Tolerance
The greatest level of pain which a subject is prepared to tolerate; it is the subjective experience of the individual.

Paresthesia
An abnormal sensation, not considered to be unpleasant, that can be either spontaneous or evoked

Perception
The process of recognizing, defining, and responding to pain

Peripheral Neuropathic Pain
Pain initiated or caused by a primary lesion or dysfunction in the peripheral nervous system; conditions include diabetic peripheral neuropathy, post-herpetic neuralgia, trigeminal neuralgia.

Peripheral Sensitization
Increased response by injured nocieptors to noxious stimuli; a key peripheral mechanism of neuropathic pain.

Physical Dependence
Potential for withdrawal symptoms if the opioid is abruptly stopped or an antagonist is administered; not the same as addiction.

Pseudoaddiction
A mistaken diagnosis of addiction; used when patients with under-treated pain exhibit behaviors often seen in addictive disease (e.g., escalating demands for larger opioid doses); behaviors typically resolve when pain is effectively treated.

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S

Sensitization
An increased sensitivity of a receptor after repeated activation by a noxious stimuli.

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T

Tolerance
A process characterized by either the decreasing effects of a drug at its previous dose, or the need for a higher dose to maintain an effect; not the same as addiction

Transduction
Conversion of one form of energy to another, made possible by an action potential

Transmission
The movement of pain impulses from the site of transduction to the brain

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U

Upregulation
An increase in a cellular component (e.g., the number of opioid receptors) that makes the cells more sensitive to a drug or other agent. 

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W

Wind-Up
Progressive increase in excitability and sensitivity of spinal cord neurons, leading to persistent, increased pain

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Definitions compiled from Pasero C, McCaffery M. Pain assessment and pharmacologic management.  St. Louis, Mosby.  2011; International Association for the Study of Pain (http://www.iasp.org/).