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Many Factors Influence Pain Perception
Monday June 7, 2010


Pain affects more than 50 million people in the U.S. each year, and one in four Americans suffers from persistent pain, according to the National Pain Foundation. Thanks to advances in medicine, physical therapists understand pain better than they did years ago and customize their therapy to address the source of the patient’s discomfort.

However, pain experts say therapists also need to know the individual factors that can contribute to pain. By understanding variations in pain responses, PTs can recognize patients at risk of persistent pain early and better tailor therapy, they say.

“There is great variability in pain reporting. We should embrace it, rather than blame the patient,” says Steven George, PT, PhD, associate professor and assistant chair, Department of Physical Therapy, University of Florida, Gainesville.

George co-presented a symposium, “Factors That Influence Musculoskeletal Pain,” at an American Physical Therapy Association meeting in February with Laura Frey Law, PT, PhD, of the University of Iowa, Iowa City.

“Pain is very complex. It is both a sensory and emotional experience,” says Law, an assistant professor at the university’s graduate program in physical therapy and rehabilitation science. “All kinds of things contribute to pain.”

Factors that Influence Pain
Pain has biological, psychological and social components, according to the biopsychosocial model of pain. Biological factors that can vary pain perception include the person’s sex, genetics and number of nociceptors, or pain receptors, in the body.

Social and cultural factors influencing pain intensity might include an expectation that “pain is something you just deal with” (less likely to communicate pain) and an overly solicitous family caregiver (more likely to communicate pain).

Some psychological issues that can worsen pain follow:
• Fear of pain, which can lead to a patient not moving, especially when a certain movement caused pain in the past
• Pain “catastrophizing” — an inability to stop thinking about one’s pain and to characterize pain as unbearable, which increases activity in areas of the brain related to anticipation of pain, according to several studies
• Negative affect (neuroticism) — a more irritable or anxious personality, which may be a precursor to pain-related fear or catastrophizing
• Depression
• Emotional stress
• Gender and Genetics

Many studies indicate differences between women and men for pain. For instance, women report certain pain conditions, such as fibromyalgia, more often than men. Research by Law and colleagues may explain one reason why.

In a study in the Nov. 30, 2008, issue of the journal Pain, they found no difference between how often men and women rate local pain, but a large difference in frequency of reporting referred pain. Compared with 80% of women, only about 45% of men reported referred pain in the anterior ankle after injection of an acidic solution into the anterior shin muscle.

Her research indicates that women may have central sensitization-altered central nervous system processing of nociceptor signals. She says this theory may help explain why many pain conditions occur more often in women than men.

Genetics also plays a role in pain, as researchers have found that some genes are linked to a higher predisposition for pain. The COMT gene — the most studied “pain gene” — is responsible for only 10% of pain perception, according to George. “Genes are a factor in pain but not the [only] factor,” he says.

In fact, our genes interact with emotional and social factors for pain perception. When patients have both the COMT gene and a tendency for pain catastrophizing, they feel more intense pain than patients who have just one of these factors, George and his co-workers found in a study of shoulder pain published in 2008.

Assessing Pain
Because psychosocial factors have a great impact on pain perception and many of these factors are modifiable, some pain researchers believe that clinicians should try to determine their patient’s thoughts and attitudes about pain.

George and Law offer these tips for a more comprehensive assessment of pain:
Assess pain at rest and during movement.

Ask how severe the patient’s original pain episode was.

When asking the patient, “What was the worst pain you had in the last seven days?” the therapist might also ask him or her to describe anything important or unusual going on at the time in terms of physical activity, work stress or family.

Screen for pain-related fear. Use surveys, such as the Fear-Avoidance Beliefs Questionnaire (designed for back pain) and the Pain Catastrophizing Scale.

Teaching Pain Self-Management
Since the mid-1980s, some experts have advocated the use of cognitive-behavioral therapy for treating pain. Several studies show that CBT is effective in treating chronic and acute pain and disability.

This approach seeks to enhance patients’ pain control using psychological techniques, including the idea that we can change the way we think and behave to feel better, explains Katherine Beissner, PT, PhD, professor in the Department of Physical Therapy at Ithaca (N.Y.) College.

“CBT is consistent with physical therapy intervention in that both promote adoption of self-management strategies and use some similar techniques,” she says.

Examples of techniques used in both PT and CBT, according to Beissner, are muscle relaxation and graded activity, which uses a quota system, such as a set number of exercises.

“I think all [PTs] know these techniques, but they are not always applying them to pain patients,” Beissner says. “For instance, we teach muscle relaxation to pulmonary rehab patients but don’t always think of applying it to pain patients.”

Incorporating CBT into PT may be as simple as addressing patients’ fears about performing therapeutic exercises. “We need to help patients realize that their negative thoughts and attitudes are not helpful and may interfere with their response to pain,” Beissner says.

PTs may need to refer some extremely fearful or depressed patients to mental health professionals. For many patients, however, PTs can introduce techniques that focus attention away from the pain while encouraging activity, such as imagery (visualization) or performing pleasurable physical activities.

Yet a survey that Beissner conducted of 152 geriatric and orthopedic PTs found a minority using CBT techniques when treating older patients with chronic pain. The survey, published in May 2009 in the journal Physical Therapy, found that most respondents believed they lacked the skills.

George believes it is important for PTs to be open to treatment strategies such as CBT. He says, “Pain is rampant, and the traditional techniques don’t work very well.” •

Kathleen Louden is a freelance writer.

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Monday June 7, 2010
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