Oct. 19, 2010 -- Having the form of a gene associated with low sensitivity to pain may not automatically protect people from developing chronic pain after surgery, a new study suggests.
"Even if you have the form of this gene that is thought to protect, it didn't protect from this kind of chronic pain [after surgery]," says researcher Craig Hartrick, MD, director of anesthesiology research at Beaumont Hospitals, Royal Oak and Troy, Mich., and discipline director for pharmacology, Oakland University's William Beaumont School of Medicine, Rochester, Mich.
Rather, anxiety seems to play a role in whether people suffer chronic pain after surgery, he says.
He presented the findings at Anesthesiology 2010, the annual meeting of the American Society of Anesthesiologists in San Diego.
A gene known as COMT relates to the ability of the body to metabolize epinephrine, the fight-or-flight hormone, Hartrick says. Those with a certain form of the gene that results in lower epinephrine levels are thought to be less sensitive to pain.
In a previous study by others, Hartrick says, researchers found that the COMT gene form associated with low pain sensitivity protected patients from developing jaw pain. So he decided to focus on pain after shoulder surgery known as rotator cuff surgery, but found different results.
''We did not find evidence to support this protective effect of genes associated with low pain for rotator cuff surgery," Hartrick says.
He evaluated 129 patients after rotator cuff surgery, following them to see how many were still in pain three months after the surgery. He found 33% of those who had the low-sensitivity form of the gene from both parents had persistent pain three months after surgery. He would have expected none to have pain three months later.
What explains the pain? Perhaps anxiety, he says. Those who scored higher on an anxiety test before surgery had higher pain three months after. "There was a strong association between anxiety and the development of post-surgery pain," he says. "That could confuse the results [of other studies]."
The jaw pain study did not consider anxiety, he says.
The anxiety Hartrick is focusing on isn't the typical anxiety most patients have right before surgery, but anxiety as a trait. "They're just nervous people," he says.
While pre-surgery jitters can be calmed with medication, he says, "you can't change your personality."
However, even if you have this anxiety trait, the situation isn't hopeless after surgery. "It may just take longer for you to recover fully."