CHRONIC PAIN GLOSSARY
PAIN
An unpleasant sensory and emotional experience associated
with actual or potential tissue damage, or described in terms of
such damage.
Note: Pain is always subjective. Each individual learns the
application of the word through experiences related to injury in
early life. Biologists recognize that those stimuli which cause
pain are liable to damage tissue. Accordingly, pain is that
experience we associate with actual or potential tissue damage.
It is unquestionably a sensation in a part or parts of the body,
but it is also always unpleasant and therefore also an emotional
experience. Experiences which resemble pain but are not
unpleasant, e.g., pricking, should not be called pain. Unpleasant
abnormal experiences (dysesthesias) may also be pain but are not
necessarily so because, subjectively, they may not have the usual
sensory qualities of pain.
Many people report pain in the absence of tissue damage or
any likely pathophysiological cause; usually this happens for
psychological reasons. There is usually no way to distinguish
their experience from that due to tissue damage if we take the
subjective report. If they regard their experience as pain and if
they report it in the same ways as pain caused by tissue damage,
it should be accepted as pain. This definition avoids tying pain
to the stimulus. Activity induced in the nociceptor and
nociceptive pathways by a noxious stimulus is not pain, which is
always a psychological state, even though we may well appreciate
that pain most often has a proximate physical cause.
ALLODYNIA
Pain due to a stimulus which does not normally provoke
pain.
Note: The term allodynia was originally introduced to
separate from hyperalgesia and hyperesthesia, the conditions seen
in patients with lesions of the nervous system where touch, light
pressure, or moderate cold or warmth evoke pain when applied to
apparently normal skin. Allo means "other" in Greek and is a
common prefix for medical conditions that diverge from the
expected. Odynia is derived from the Greek word "odune" or
"odyne," which is used in "pleurodynia" and "coccydynia" and is
similar in meaning to the root from which we derive words with -
algia or -algesia in them. Allodynia was suggested following
discussions with Professor Paul Potter of the Department of the
History of Medicine and Science at The University of Western
Ontario.
The words "to normal skin" were used in the original
definition but later were omitted in order to remove any
suggestion that allodynia applied only to referred pain.
Originally, also, the pain-provoking stimulus was described as
"non-noxious." However, a stimulus may be noxious at some times
and not at others, for example, with intact skin and sunburned
skin, and also, the boundaries of noxious stimulation may be hard
to delimit. Since the Committee aimed at providing terms for
clinical use, it did not wish to define them by reference to the
specific physical characteristics of the stimulation, e.g.,
pressure in kilopascals per square centimeter. Moreover, even in
intact skin there is little evidence one way or the other that a
strong painful pinch to a normal person does or does not damage
tissue. Accordingly, it was considered to be preferable to define
allodynia in terms of the response to clinical stimuli and to
point out that the normal response to the stimulus could almost
always be tested elsewhere in the body, usually in a
corresponding part. Further, allodynia is taken to apply to
conditions which may give rise to sensitization of the skin,
e.g., sunburn, inflammation, trauma.
It is important to recognize that allodynia involves a
change in the quality of a sensation, whether tactile, thermal,
or of any other sort. The original modality is normally non-
painful, but the response is painful. There is thus a loss of
specificity of a sensory modality. By contrast, hyperalgesia
(q.v.) represents an augmented response in a specific mode, viz.,
pain. With other cutaneous modalities, hyperesthesia is the term
which corresponds to hyperalgesia, and as with hyperalgesia, the
quality is not altered. In allodynia the stimulus mode and the
response mode differ, unlike the situation with hyperalgesia.
This distinction should not be confused by the fact that
allodynia and hyperalgesia can be plotted with overlap along the
same continuum of physical intensity in certain circumstances,
for example, with pressure or temperature.
See also the notes on hyperalgesia and hyperpathia.
ANALGESIA
Absence of pain in response to stimulation which would
normally be painful.
Note: As with allodynia (q.v.), the stimulus is defined by
its usual subjective effects.
ANESTHESIA DOLORASA
Pain in an area or region which is anesthetic.
CAUSALGIA
A syndrome of sustained burning pain, allodynia, and
hyperpathia after a traumatic nerve lesion, often combined with
vasomotor and sudomotor dysfunction and later trophic changes.
CENTRAL PAIN
Pain initiated or caused by a primary lesion or dysfunction
in the central nervous system.
DYSESTHESIA
An unpleasant abnormal sensation, whether spontaneous or
evoked.
Note: Compare with pain and with paresthesia. Special cases
of dysesthesia include hyperalgesia and allodynia. A dysesthesia
should always be unpleasant and a paresthesia should not be
unpleasant, although it is recognized that the borderline may
present some difficulties when it comes to deciding as to whether
a sensation is pleasant or unpleasant. It should always be
specified whether the sensations are spontaneous or evoked.
HYPERALGESIA
An increased response to a stimulus which is normally
painful.
Note: Hyperalgesia reflects increased pain on suprathreshold
stimulation. For pain evoked by stimuli that usually are not
painful, the term allodynia is preferred, while hyperalgesia is
more appropriately used for cases with an increased response at a
normal threshold, or at an increased threshold, e.g., in patients
with neuropathy. It should also be recognized that with allodynia
the stimulus and the response are in different modes, whereas
with hyperalgesia they are in the same mode. Current evidence
suggests that hyperalgesia is a consequence of perturbation of
the nociceptive system with peripheral or central sensitization,
or both, but it is important to distinguish between the clinical
phenomena, which this definition emphasizes, and the
interpretation, which may well change as knowledge advances.
HYPERESTHESIA
Increased sensitivity to stimulation, excluding the special
senses.
Note: The stimulus and locus should be specified.
Hyperesthesia may refer to various modes of cutaneous sensibility
including touch and thermal sensation without pain, as well as to
pain. The word is used to indicate both diminished threshold to
any stimulus and an increased response to stimuli that are
normally recognized.
Allodynia is suggested for pain after stimulation which is
not normally painful. Hyperesthesia includes both allodynia and
hyperalgesia, but the more specific terms should be used wherever
they are applicable.
HYPERPATHIA
A painful syndrome characterized by an abnormally painful
reaction to a stimulus, especially a repetitive stimulus, as well
as an increased threshold.
Note:It may occur with allodynia, hyperesthesia,
hyperalgesia, or dysesthesia. Faulty identification and
localization of the stimulus, delay, radiating sensation, and
after-sensation may be present, and the pain is often explosive
in character. The changes in this note are the specification of
allodynia and the inclusion of hyperalgesia explicitly.
Previously hyperalgesia was implied, since hyperesthesia was
mentioned in the previous note and hyperalgesia is a special case
of hyperesthesia.
HYPOALGESIA
Diminished pain in response to a normally painful
stimulus.
Note: Hypoalgesia was formerly defined as diminished
sensitivity to noxious stimulation, making it a particular case
of hypoesthesia (q.v.). However, it now refers only to the
occurrence of relatively less pain in response to stimulation
that produces pain. Hypoesthesia covers the case of diminished
sensitivity to stimulation that is normally painful.
The implications of some of the above definitions may be
summarized for convenience as follows:
Allodynia: lowered threshold: stimulus and response mode
differ
Hyperalgesia: increased response: stimulus and response mode
are the same
Hyperpathia: raised threshold: stimulus and response mode
may be the increased response: same or different
Hypoalgesia: raised threshold: stimulus and response mode
are the same lowered response:
The above essentials of the definitions do not have to be
symmetrical and are not symmetrical at present. Lowered threshold
may occur with allodynia but is not required. Also, there is no
category for lowered threshold and lowered response - if it ever
occurs.
HYPOESTHESIA
Decreased sensitivity to stimulation, excluding the special
senses.
Note: Stimulation and locus to be specified.
NEURALGIA
Pain in the distribution of a nerve or nerves.
Note: Common usage, especially in Europe, often implies a
paroxysmal quality, but neuralgia should not be reserved for
paroxysmal pains.
NEURITIS
Inflammation of a nerve or nerves.
Note: Not to be used unless inflammation is thought to be
present.
NEUROGENIC PAIN
Pain initiated or caused by a primary lesion, dysfunction,
or transitory perturbation in the peripheral or central nervous
system.
NEUROPATHIC PAIN
Pain initiated or caused by a primary lesion or dysfunction
in the nervous system.
Note: See also Neurogenic Pain and Central Pain. Peripheral
neuropathic pain occurs when the lesion or dysfunction affects
the peripheral nervous system. Central pain may be retained as
the term when the lesion or dysfunction affects the central
nervous system.
NEUROPATHY
A disturbance of function or pathological change in a nerve:
in one nerve, mononeuropathy; in several nerves, mononeuropathy
multiplex; if diffuse and bilateral, polyneuropathy.
Note: Neuritis (q.v.) is a special case of neuropathy and is
now reserved for inflammatory processes affecting nerves.
Neuropathy is not intended to cover cases like neurapraxia,
neurotmesis, section of a nerve, or transitory impact like a
blow, stretching, or an epileptic discharge. The term neurogenic
applies to pain due to such temporary perturbations.
NOCIEPTOR
A receptor preferentially sensitive to a noxious stimulus or
to a stimulus which would become noxious if prolonged.
Note: Avoid use of terms like pain receptor, pain pathway,
etc.
NOXIOUS STIMULUS
A noxious stimulus is one which is damaging to normal
tissues.
Note: Although the definition of a noxious stimulus has been
retained, the term is not used in this list to define other
terms.
PAIN THRESHOLD
The least experience of pain which a subject can
recognize.
Note: Traditionally the threshold has often been defined, as
we defined it formerly, as the least stimulus intensity at which
a subject perceives pain. Properly defined, the threshold is
really the experience of the patient, whereas the intensity
measured is an external event. It has been common usage for most
pain research workers to define the threshold in terms of the
stimulus, and that should be avoided. However, the threshold
stimulus can be recognized as such and measured. In
psychophysics, thresholds are defined as the level at which 50%
of stimuli are recognized. In that case, the pain threshold would
be the level at which 50% of stimuli would be recognized as
painful. The stimulus is not pain (q.v.) and cannot be a measure
of pain.
PAIN TOLERANCE LEVEL
The greatest level of pain which a subject is prepared to
tolerate.
Note: As with pain threshold, the pain tolerance level is
the subjective experience of the individual. The stimuli which
are normally measured in relation to its production are the pain
tolerance level stimuli and not the level itself. Thus, the same
argument applies to pain tolerance level as to pain threshold,
and it is not defined in terms of the external stimulation as
such.
PARESTHESIA
An abnormal sensation, whether spontaneous or evoked.
Note: Compare with dysesthesia. After much discussion, it
has been agreed to recommend that paresthesia be used to describe
an abnormal sensation that is not unpleasant while dysesthesia be
used preferentially for an abnormal sensation that is considered
to be unpleasant. The use of one term (paresthesia) to indicate
spontaneous sensations and the other to refer to evoked
sensations is not favored. There is a sense in which, since
paresthesia refers to abnormal sensations in general, it might
include dysesthesia, but the reverse is not true. Dysesthesia
does not include all abnormal sensations, but only those which
are unpleasant.
PERIPHERAL NEUROGENIC PAIN
Pain initiated or caused by a primary lesion or dysfunction
or transitory perturbation in the peripheral nervous system.
Peripheral neuropathic
pain
Pain initiated or caused by a primary lesion or dysfunction
in the peripheral nervous system.