The Biopsychosocial Model Helps Explain Complex Differences in Pain

When understanding biology alone is not enough.

At the North American Pain School, Roger Fillingim recalled his experiences as a clinician treating chronic pain nearly twenty-five years ago. One particular patient stood out to him: a gentleman with chronic low back pain, two unsuccessful surgeries, and multilevel disc degeneration. For many pain clinicians and researchers, these details about the patient’s medical history, even today, would be the focus of their attention.

However, there were many more important factors at play in the patient’s life that may have been contributing to his pain experience: he was a 45-year-old former iron worker on worker’s compensation, had not completed high school and was functionally illiterate, and had a history of panic disorder, depression, and heart attack. Unfortunately, many people who treat and research pain may often overlook these important factors.

“Let’s treat his pain as though it’s a single entity, and ignore everything else about his life—that’s not going to work very well for us,” Fillingim said. “And this is not an uncommon example; it’s relatively common for people with long-term pain.”

The take-home message of Fillingim’s talk was that understanding the experience of patients with chronic pain, and knowing how best to treat them, requires a perspective that goes beyond considering only biological factors.

“What we now think is particularly helpful is the biopsychosocial model, which tells us that the experience of pain and responses to pain are sculpted by complex and dynamic interactions of biological, psychological, and sociocultural factors,” he said.

Advancing beyond the biomedical model

The biopsychosocial model of pain was introduced by George Engel in 1977 in an article in Science. Engel was frustrated that the biomedical field was not appreciating the complexity of factors that contribute to disease. He argued that the biomedical model of understanding disease needed to be replaced, for several reasons.

For example, biological processes that go awry in disease do not by themselves explain the clinical symptoms or maladies that people may have. While an x-ray or MRI scan can show where a physical injury occurs in the body, the pictures from these scans do not fully explain differences in the amount of pain or disability that two individuals living with the same condition may show.

“We don’t treat disease—we treat people in a context of their lives who happen to have a disease,” said Fillingim. “And the life conditions in which people find themselves have a tremendous impact on the disease itself.”

Fillingim explained how psychosocial factors also influence whether people think they are sick. There are some symptoms that are accepted as ‘normal’ in some cultures or circumstances, whereas the same symptoms in other cultures or circumstances might represent illness. Additionally, social interactions between patients and providers have a profound impact on treatment outcomes, especially when it comes to pain management.

Examples of the biopsychosocial model of pain

Building on the purely biomedical model of pain, the biopsychosocial model of pain takes into account complex interactions between biological factors (e.g., hormones, genetics, endogenous opioids), psychological factors (e.g., mood, pain coping, pain catastrophizing), and social factors (e.g., gender roles, ethnic identity, discrimination, provider bias) that may contribute to pain. As a result, Fillingim said the biopsychosocial model is better able to answer complex questions related to pain treatment and research, such as who is at higher risk for certain types of pain, why individuals may respond differently to pain, and why it is generally ineffective to provide only a single form of treatment for pain.

For example, consider why some people react to painful stimuli in vastly different ways. Fillingim tested this in an experimental setting by applying a 48-degree Celsius (118 degree Fahrenheit) heat stimulus on a healthy group of 321 study participants. He found that there were remarkable differences in how people rated the severity of their pain, even though they had received the same pain stimulus. Fillingim explained how a variety of factors such as sex, race, age, genetics, blood pressure, expectations, anxiety, and the influence of the experimenter could contribute to these differences in pain sensitivity. “These are the individual differences that we’re faced with. Most people see this as a nuisance; I see it as a career,” he said humorously.

Indeed, Fillingim’s work has revealed several biopsychosocial factors that may contribute to individual differences in pain, such as the interaction between genetics and sex in pain sensitivity; the interaction between genetics and ethnicity in pain sensitivity; and the interaction between sex, stress, and genetics in pain sensitivity and pain relief; the influence of sleep quality and the interaction between stress and genetics in jaw pain; ethnic differences in older adults with knee osteoarthritis; and the influence of genetics and psychological factors in shoulder pain.

“We need to maintain this perspective that pain is complex,” he said. “Pain is not in a niche. It is in a complex person living in a complex world.”

Pauline Voon is a PhD candidate in population and public health at the University of British Columbia, Vancouver, Canada