An introductory lecture for those interested in pain science

1. An Introduction to the Science of Pain –
Myths and Realities
Psychology
Neuroscience
Physiology

4. Epidemiology
■ Approximately 50
million Americans
experience chronic pain
■ 18-34% of US
population deals with
chronic pain
■ Emphasizes critical
need for pain
management
■ Close to half of the
American population
will seek care for a
pain problem at some
point during their lives
■ 8% of Americans have
“high impact” chronic
pain

5. Epidemiology
■ Prevalence of low back pain
■ Any low back pain
■ 60-80%
■ Any back pain persisting at
least 2 weeks
■ 7%
■ Back pain with features of
sciatica lasting at least 2 weeks
■ 1.6%
■ Lumbar spine surgery
■ 1-2%

6. Epidemiology
■ Headache pain
■ 90% of Americans
experience non-migraine
headaches
■ Migraines
■ ~25 million Americans
■ Arthritis pain
■ 1 in 6 adults
■ Cancer pain
■ Majority of cancer pain patients
experience some level of pain
■ Some statistics indicate that
many of these patients do not
receive adequate pain relief
■ Palliative care

7. Defining Pain
■ What exactly is pain?
■ How do you define
pain?
■ Noxious – tissue
damaging stimuli
■ Nociceptors – the
receptors of the body
that convey pain
information
■ What are some of the
ways you can describe
pain?
■ Try to come up with
terms to describe
painful events…

8. What is pain?
“Something that hurts.”
UNC Student Female
“Unpleasant sensation.”
UNC Student, male
“A signal that tells you that you should not be doing something. Tells you that
something you are doing is bad.”
UNC student, male
“Pain means that you should stop.”
UNC student, female
“Something I don’t like. Try to avoid.”
UNC student, male
“Something bad, can be physical or emotional. Something you want to stay away from.”
UNC student, female

9. Definitions of Pain
■ What do these definitions have in common?
■ Are these concepts of pain a product of evolution
or are they produced by our experiences with
pain?
■ Bonica’s studies with puppies
■ Completely isolated from pain experience
■ Fluffy environment
■ How did they react to painful stimuli?

10. Common Definitions of Pain
■ Most people define
pain as a perception
that occurs following
tissue damage
■ This is a very
dangerous
misconception
■ Pain is designed as an
early warning system
■ Pain occurs BEFORE
tissue damage, as
stimuli APPROACH
tissue damaging range
■ So the organism can
escape the potential
injury!

11. What is pain?
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 cause 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 (dyesthesias) 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 way 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. (International Association for the Study of Pain, 1979)
Pain is what the patient says it is and exists when he says it does.
(Meinhard and McCaffery, 1984)

12. The Meaning of Pain
■ “global” pain
■ all-encompassing multidimensional pain space
■ gestalt
■ Loeser (1980)
■ global pain should include
■ sensory qualities
■ suffering
■ pain behavior
■ many other potential components
■ motivation

13. The Meaning of Pain
■ Variety of meanings given to the word
“pain”
■ Pure pain sensation
■ Somatosensory sensations
■ Emotional
■ Motivational
■ Cognitive
■ Suffering

14. Difficulties in Pain Measurement
■ Wall (1983)
■ pain is “always
subjective”
■ Search for an
objective pain
measure, comparable
between participants
■ No real objective
assessments of a
perceptual state
■ So, how can we assess
pain?

15. What makes chronic pain so difficult?
Social and psychological factors play a pivotal role in presentation
and response to treatment
Environment
Social motivations
Secondary gain

16. Parallel Processing Model of Pain
Perception
Emotional/Motivational
Autonomic
Discriminative
Motor Reflex
Spinal
Input
these many components of pain perception can interact with one another

17. Situational, Behavioral, and Emotional Factors
and Pain Perception
NOXIOUS
STIMULUS
Situational Factors Behavioral Factors Emotional Factors
*expectation
*control
*relevance
*coping style
*overt distress
*social response
*fear
*anger
*frustration
*competition
PAIN
SENSATION
*sex
*age
*cognitive level
*previous pains
*family learning
*culture
A model of the situational, behavioral, and emotional factors that can modify pain perception.
taken from McGrath 1990

18. Anatomy of Pain
■ Primary systems for
pain perception
■ Receptors - nociceptors
■ C fibers
■ A delta
■ Polymodal
nociceptors
■ Pathway
■ Spinothalamic tract
■ Brain areas responsible
for pain perception
■ Primary somatosensory
cortex
■ Anterior cingulate
cortex
■ Prefrontal cortex
■ Tempero-parietal
cortex
■ Periaqueductal grey

19. Spinothalamic Tract

23. The general response to patients with
chronic pain…

24. Analgesia
■ Not just relief of subjective pain
■ Can be debilitating
■ A host of other physiological factors are
influenced by presence of pain
■ Sympathetic nervous system
■ Hypothalamic-pituitary axis
■ Importance of adequate pain relief

25. Consequences of Inadequate Analgesia
■ Impairment of immune function
■ Increased ability of blood to clot
■ Exacerbate injury
■ Prevent wound healing
■ Increase susceptibility to infection
■ Prolong hospitalization

26. Consequences of Inadequate Analgesia
■ Fight or flight
■ Release of stress
hormones
■ Epinephrine
■ Norepinephrine
■ Glucagon
■ Cortisol
■ Aldosterone
■ Thyroid stimulating
hormone
■ Growth hormone
■ Promote breakdown of
body tissues and water
retention
■ Increase blood glucose
■ Increase body’s metabolic
rate
■ Increase heart rate, blood
pressure, cardiac output,
and inotropic state of heart
■ Impair normal
gastrointestinal functioning

27. Importance of Subjective Ratings of Pain
■ Pain is defined by the person experiencing it
■ Most common means of assessing pain is by
subjective report of the person/participant
■ Most common means of assessing pain rely on
subjective ratings
■ These ratings are the primary tool for determining
if pain management is effective

28. Pain Measurement
■ If the answers to the question “What is
pain?” are so varied, how can one measure
pain?
■ A person can easily report whether or not a
stimulus is painful
■ But how can they report the degree of pain
they are experiencing?

29. Pain Measurement
■ How can one define and assess the validity of a
pain measure?
■ Is pain a unidimensional or a multidimensional
construct?
■ Can one find a truly objective measure of a
subjective sensation?

30. The Meaning of Pain
■ Melzack (1973) The Puzzle of Pain
■ Number of pain qualities
■ Ranges from a single quality
■ purely emotional
■ purely sensory)
■ To as many as 5 qualities
■ affective
■ motivational
■ cognitive aspects
■ behavior

31. Components of Pain
■ Melzack and Casey (1968)
■ Suggested 3 dimensions
■ Sensory-discriminative
■ Motivational-affective
■ Cognitive-evaluative

32. Multiple Dimensions of the Pain
Experience
■ Multidimensional scaling studies
demonstrate anywhere from 2-5 factors
■ Two of the factors are
■ Pain Intensity
■ Pain Unpleasantness
■ Experience of pain may be a gestalt
■ more than the sum of its parts
■ To adequately assess pain, one needs to
assess as many of these parts as possible

33. Multidimensional Models of Pain
■ Multiple Components of the Pain
Experience
■ Sensory/Physiological
■ Cognitive
■ Behavioral
■ Affective/Emotional
■ Motivational

34. Complexities of Pain
■ Pain as a perceptual
construct
■ Extremely difficult to
define
■ Extremely difficult to
assess
■ Very common as a
clinical symptom
■ However, very difficult to
describe to someone else
■ Think of a pain
experience that you have
had
■ Try to describe it to your
neighbor
■ Unless she has had a
similar experience, this
can be very difficult

35. Sensation, Perception, Comprehension
■ Every experience you
have with something
in your environment
has at least three
components, if it
reaches conscious
awareness
■ Sensation – the
recognition by your
nervous system of an
outside event
■ Perception – your
awareness of that event
■ Comprehension – your
understanding of the
meaning of the event

36. The Unique Nature of Pain
■ Can you have a perception of pain without
noxious inputs (sensation)?
■ Can you have sensation of pain without
perception?
■ Can you have perception of pain without
comprehension?

37. Examples
■ Have you ever given a
child a shot?
■ Do they yell when you
clean the site with
alcohol?
■ The child expects
(comprehension) pain
with a shot
■ Therefore, can feel pain
when you touch her!
■ Have you ever been
hiking and come home
with a cut or a bruise
that you don’t
remember getting?
■ Where there noxious
inputs?
■ Why weren’t you
aware of them?

38. The Nature of the Body’s Reaction to
Pain
■ Our perceptual systems are designed to
understand the events that happen to us
■ To assign them meaning
■ This means that sensation, perception, and
comprehension may not occur in sequential
order!

39. A Child’s Story
■ When I was young, my brother and I used to enjoy stomping in mud
puddles. One weekend, after a brisk rain, we trudged outside and took
on mud hole after mud hole, trying to splash one another as
impressively as possible. After a particularly good splash, my brother
looked down at my feet, his mouth open, and pointed. I looked down
to see a streak of red in the puddle. I pulled my foot up to see a large
piece of glass lodged in my Snoopie galoshes – and my foot. I started
to scream. My father came out, and began trying to remove the
galoshes, to get a look at the injury.. I writhed and yelled, protesting
my agony. My father finally sat me up with a start, and exclaimed, “I
will bet you didn’t start crying until you saw it.” I stopped crying, and
realized he was right. So I sat still as he removed the 4 inch piece of
glass.

40. Why is this important to health
professionals?
■ Understanding that a
patient may have pain
even when we don’t
see anything wrong
■ Also understanding
that what a patient
knows may impact the
amount of pain she
feels
■ Finally, recognizing
that we can never
really know how
much a patient is
hurting
■ We have to ask, and
ask often!

41. Pain Measurement Scales
■ Numerical Rating Scales
■ Visual Analogue Scales
■ Verbal Rating Scales
■ Magnitude Matching
■ Behavioral Measures
■ Physiological Measures

42. Multidimensional Models of Pain
■ Multiple Components of the Pain
Experience
■ Sensory/Physiological
■ Cognitive
■ Behavioral
■ Affective/Emotional
■ Motivational

43. Complexities of Pain
■ Pain as a perceptual
construct
■ Extremely difficult to
define
■ Extremely difficult to
assess
■ Very common as a
clinical symptom
■ Specific issues related
to pain in the clinical
environment
■ What aspects of pain
are important to
assess?
■ Why?

44. Prevalence of Undertreated Pain
■ Study to Understand
Prognoses and
Preferences for
Outcomes and Risks of
Treatment
■ 50% of patients
reported unrelieved pain
■ 15% reported extremely
severe pain
■ Cancer Pain
■ Study of 54 cancer
treatment centers
■ 67% of outpatients
reported pain in the
previous week
■ 42% were not given
adequate analgesia
■ Inadequate treatment
of pain at end of life

45. Barriers to Optimal Pain Control
■ Lack of knowledge
■ Very few medical schools
have courses on pain
■ Oncologists
■ 75% rated pain
management training as fair
to poor
■ Many schools have only 1-2
lectures, despite prevalence
of pain as syndrome as well
as symptom
■ This is improving, but
slowly
■ Inadequate pain assessment
■ MAJOR predictor of
inadequate pain control
■ Difficulties of measuring
pain
■ Pain as subjective
■ Sometimes, can only
measure pain relatively,
within a given patient
■ Measuring CHANGE in pain
ratings

46. Faking Pain
■ Worker’s Compensation
■ Issues of Secondary Gain
■ Issues that may lead an individual to report
pain, to achieve a secondary benefit
■ Can be very difficult to determine if an
individual is malingering pain

47. Malingering
■ A constant challenge
to all aspects of health
professional
interactions with pain
patients
■ Describe the “classic”
patient who is “faking
pain”
■ How can you tell
■ The classic stereotype
of a malingering
patient can often look
strikingly similar to a
chronic pain patient
receiving inadequate
treatment
■ Depression
■ Hysterical
■ “Doctor shopping”

48. Detection of Bias in the Pain Responder
■ Minnesota Multiphasic Personality
Inventory II (Greene, R. L. (1991)
■ Gracely (1983) suggests the use of several of
the MMPI scales to detect biases in
responding in pain assessment
■ F-scale: “Faking” scale
■ L-scale: “Lying” scale
■ K-scale: “Defensiveness” scale

49. Problems with the Use of these Tools to
Measure Bias
■ Many problems with the accuracy of these scales
■ Biases in responding to the MMPI-II may not
indicate biases in response to pain measurement
■ “The only time my children tell the truth is when
they are in pain.” Bill Cosby
■ Need specific tools for measuring these features in
pain report
■ Again, return to problem of how to determine
accuracy

50. Where does this leave us?
■ If we accept that we have a duty to assess
and attempt to treat pain, where does this
leave our responsibility?
■ What about patients who are malingering or
faking pain?
■ How do we determine if patients are
genuinely in pain?

51. Responsibility
■ The answer, as difficult as
this may seem, is that we
simply have to take the
patient at her word
■ We must believe that a
patient is in pain who
reports pain, until proven
otherwise
■ When reasonable
doubts are present
regarding validity of
pain report, physicians
may take into account
other causes
■ But remember - the
only valid pain report
comes from the patient
herself