Transcript Facial expression of pain: Prospects for improved

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A functional perspective on pain
behaviour
Kenneth M. Prkachin
University of Northern British
Columbia
Excerpts from two clinical reports
“Throughout the assessment the client did not
display any…behaviours such as…facial
grimacing…[This] leads the evaluator to believe
that the client’s primary reason for self limiting
may be due to…fear of re-injury”
“During today’s clinical assessment, significant
pain magnifying features were observed. Such
a presentation is thought to be due to acquired
overprotective behaviours”
What is the role of behaviour in the
pain system?
Sensory model: simple consequence of a
discrete sensory system (Descartes,1649)
Unitary model: a form of operant
behaviour, modifiable by its consequences
(Fordyce, 1978):
Multidimensional model: different pain
behaviors are organized in different ways
and at different levels of the nervous
system (Liebeskind & Paul, 1977)
Purpose
Describe properties of pain-related
behaviours
Illustrate some of the questions that can
be addressed through the study of pain
behaviours
Inform the debate on the function of pain
behaviours
Forms of pain behaviour
Decomposing the facial expression
of pain
FACS Cheek Raise
AU6, Orbit
squeeze 1
Facial actions elicited by four pain modalities
Pain expression
How well does expression encode pain?
How good are people at inferring
pain from facial behaviour?
Pain affect scale (Heft et al)
Slightly unpleasant
2.64
Very unpleasant
11.55
Slightly annoying
3.07
Miserable
12.85
Annoying
5.06
Very distressing
15.72
Unpleasant
5.42
Slightly intolerable 16.81
Slightly distressing
5.93
Very miserable
18.93
Slightly miserable
7.21
Intolerable
32.82
Very annoying
9.46
Very intolerable
43.49
Distressing
10.49
How good are people at inferring
pain from facial behaviour?
Type of test
Self-reportexpression
Judgeexpression
Active
.95
.02
Passive
.49
.52
Source: Prkachin, Berzins &
Mercer (1994) Pain, 58, 253-259
Perceiving pain in others: effects of
experience
Enhanced underestimation among health-care
providers
15
Controls
Professionals
Patients
10
Source: Prkachin, Solomon,
Hwang & Mercer (2001). Pain
Research and Management, 6,
105-112.
5
0
Active
Passive
Do pain behaviours predict disability?
Multivariate prediction of disability—low
back study
Goal: identify set of predictors of poor
outcomes in first episode, low-back injured
workers
Comprehensive set of predictors in four
domains: physical, psychosocial,
occupational, pain behaviour
Multivariate prediction of
disability—low back study
148 first-episode, subabute low-back pain
patients
Physical exam, psychological tests, workplace
assessment
Measurement of pain behaviour in physical
exam: guarding, rubbing, words, sounds, facial
expression
Follow up at 3 months: return-to-work, time lost,
rehabilitation costs, self-reported disability
Relationships between pain
behaviours and disability outcomes
Measures of disability
(Lack of) return to work
Days lost
Rehabilitation costs
Self-report
– Quality of life (SF-36)
– Von Korff disability measure
– Western Ontario-McMaster Osteoarthritis index
(WOMAC)
– Roland-Morris
– Pain Disability Index
Relationships between pain
behaviours and disability outcomes
Pain
behaviour
RTW
Days
lost
Costs
Guarding
+
+
+
Self
reported
disability
+
Sounds
-
0
0
0
Words
0
+
+
0
Facial
expression
0
0
0
0
Multivariate model (best predictors)
Variable
No RTW Days lost
Costs
Disability
Job threatened
-
-
-
-
Problem worse
+
+
+
+
Injury intensity
0
0
0
0
Timed walk
0
+
+
+
R leg sciatica
+
0
0
+
Waddell signs
0
0
0
0
Guarding
+
+
+
+
Conclusion
A pain behaviour (facial expression) appears to
be a read-out of painful experience, adapted for
communicative purposes. It is not arbitrary and
is unlikely to reflect operant forces
A pain behaviour (guarding) appears to be a
marker of some process that contributes to
disability. Though correlated with other pain
behaviours it has different properties
Pain behaviour is not unitary
New directions
Toward automated analysis
Viewing facial expressions of pain engages
cortical areas involved in the direct experience of
pain
(Botvinick, Jha, Bylsma, Fabian, Solomon & Prkachin, (In press),
Neuroimage).
Direct experience (thermal pain)
Vicarious experience (pain expression)
fMRI
Areas jointly activated by 1st person
and 3rd person pain