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Identifying Psychological Factors That Influence Surgical Outcomes

MMPI and MPS questionnaires, as well as a psychological examination, may help determine which chronic pain patients will have successful surgical outcomes.
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Pain relief is the primary reason why patients in the United States undergo elective surgery. However, it has been reported that approximately 10% of patients who undergo surgery will develop chronic pain.1 This article points out a number of psychological factors that should be kept in mind before elective surgery is considered in patients experiencing persistent or chronic pain. To determine the best candidates for surgery, clinicians should evaluate each patient individually, taking into consideration the extensiveness of the procedure and the patient’s degree of motivation toward rehabilitation.

Thirty years ago, when I became interested in pain management, I reviewed the pain literature in depth. I was looking for a framework or model from which to evaluate and treat patients with chronic pain. At that time, I also was interested in psychophysiology and biofeedback, which I felt was complementary to my interest in pain management. The “gate control model of pain,” introduced by Ron Melzack, PhD, and Patrick Wall, MA, DM, in 1965, appealed to me because it was based on creditable, empirical evidence, and it offers practical face validity.2

Since the 1960s, psychological approaches to chronic pain have been greatly influenced by the work of Melzack and Wall. Their gate control theory offered a legitimate alternative to the dualistic approach (either psychogenic or “real” notion) to chronic pain. Since its publication, more than 2,000 peer-reviewed studies based on the gate control theory have been published.

Factors Influencing Pain Perception
Melzack et al believed there are three primary interdependent factors that influence pain: the sensory factor, the affective factor (how we cope with chronic pain), and the evaluative/cognitive factor (how we think about our pain).3 When I evaluate a pain patient who is being considered for elective surgery, my clinical impressions are based on Melzack’s model.

Although most of my colleagues in pain management are very knowledgeable about the sensory influence in pain, what they may not appreciate is how the affective and cognitive factors influence the pain signal. Pain is a perception, thus in order to be successful in treating the patient with pain, practitioners must treat the perception. In other words, one may perform an excellent surgery or intervention, but patients who are depressed, constant worriers, or who magnify their symptoms, may return 6 months later with pain that is worse.

Patient Examination
Most of my pain referrals are not overly receptive to being evaluated by a pain psychologist due to the misperception that the psychologist’s role is to determine if the patient’s pain is real or imaginary. This stereotype is based on outdated, invalid, dualistic assumptions about the either/or nature of pain.

When I initially meet pain patients, I attempt to defuse the either/or notion by drawing a Venn diagram of three interlocking circles. I inform the patients that my job is to assist the referring physician in understanding the affective and/or cognitive factors that may be influencing their pain, and not to question the validity of their pain complaints. Initially, I draw each circle so each is identical in size. After the evaluation I sit down with the patient and redraw the Venn diagram based on my clinical impression. I point out the interrelated nature of pain, how these factors contribute to their pain experience and form the basis of a treatment plan.

Figure 1. Melzack’s pain model. A, affective factor; C, cognitive factor; S, sensory factor

As illustrated in Figure 1, the dark shaded area in the very center is pain. The affective and cognitive factors are contributory, especially if the patient is depressed and is exhibiting catastrophic thinking. This is not a stimulus–response linear model, but a circular, interdependent, and reciprocal process that is very dynamic. Mood and thinking can change from day to day, and this contributes to pain levels being very labile. Another point to consider is that each pain patient is unique, which presents certain challenges to the pain specialist so as not to overgeneralize or put all pain patients in the same category.

An additional important cognitive risk factor to consider is how the patients think about their pain. Do they describe the pain as “troublesome” or is it “killing” them? The difference between these two descriptive adjectives is clinically significant. I first started to appreciate the clinical significance of catastrophic thinking after reading a study conducted by Bigos et al in 1992.4 It was an extensive and well-designed study in which more than 3,000 Boeing employees were administered the Minnesota Multiphasic Personality Inventory (MMPI). During 4 years of follow-up observation, more than 279 subjects reported acute back problems. The authors found that the most predictive individual factors for the development of back problems were job task dissatisfaction and distress as reported on the Hysteria scale (scale 3) of the MMPI. These employees were then followed for 3 years to determine if a profile could predict who would file a back injury claim. In my opinion, scale 3 is a good indicator of catastrophic thinking or what I refer to as the “Chicken Little factor.”

While at Oregon Health & Science University in 1996, my colleagues and I conducted a study to determine if we could predict, based on a psychological profile, who would fail a trial of spinal cord stimulation therapy. The Hysteria scale of the MMPI was found to be a significant predictor of trial failure.5 Patients with catastrophic thinking are easy to identify by simply asking them to describe their pain, or by administering the McGill Pain Questionnaire (MPS), with particular attention to group 16 (ie, words to describe pain: annoying, troublesome, miserable, intense, unbearable).6 Melzack constructed the MPS based on his model of pain. (I strongly recommend the third edition of his book, Handbook of Pain Assessment, for a more detailed explanation.)7

Further evidence of catastrophic thinking can be obtained by asking the patient to rate his or her pain on a 10-point visual analog scale, with 10 being the highest rating. The catastrophic pain patient usually will rate his or her pain at a 10 or higher, all the while knowing that the scale only goes to 10, and also will describe very little variability over the course of a day. These patients typically will present themselves in a dramatic fashion, usually magnifying their symptoms, which will not be consistent with physical findings. Additionally, they usually will be more antalgic and hyper-responsive to physical testing. If physiologic testing is performed, they will generally have colder extremities, elevated sweat gland activity (electrodermal response or galvanic skin response), and will exhibit higher surface muscle activity (on electromyography) readings. In the extreme, these patients may be diagnosed with some type of anxiety disorder or elevated psychophysiologic sympathetic arousal.

The surgeon who is considering an elective procedure on a pain patient who is consistent with this typology should proceed with caution. The prudent course of action should include a psychological evaluation by a pain psychologist before proceeding with any major invasive procedure.

Last updated on: November 2, 2011
First published on: September 1, 2011