A study presented at the 2009 Annual Meeting of the American Society of Anesthesiologists highlights the crucial importance of investigating multiple factors when designing studies that attempt to predict the development of persistent pain in patients.
Researchers specializing in anesthesiology and genetics at Oakland University (CA) William Beaumont School of Medicine were surprised to find that:
• Patients who carried a gene known for low sensitivity to pain
• Actually showed higher levels of pain at three months after surgery than other patients.
The study followed 58 patients who had undergone arthroscopic shoulder surgery for rotator cuff repair, a minimally invasive procedure that typically causes little postoperative pain. The patients also received nerve block anesthetics for home use to further reduce any lingering pain.
“Despite aggressive acute pain management, some patients still experienced significant pain and interference with activities that persisted for months, well beyond the usual period of healing,” said Dr. Craig T Hartrick, MD, who is Director of Anesthesiology Research at Oakland U.
The patients who still experienced pain at three months were paired with those who recovered from surgery uneventfully. Those who carried genes that better controlled the release of an enzyme known as COMT (catechol-O-methyl transferase) were examined to see if they resisted postsurgical pain better than the other patients. It has been suggested that patients with the very active form of COMT are protected from the development of temporomandibular joint dysfunction (TMJ), and possibly other forms of pain.
In the current study, patients with high anxiety before surgery had increased pain at three months, lower quality of life and increased feelings of sensitivity to pain. Again, when matched against other patients with similar anxiety levels, the low pain sensitivity COMT patients were actually experiencing the highest pain levels at three months.
“This may be explained due to the tendency for a reduced level of reported anxiety in the low pain sensitivity COMT subgroup of patients,” said Dr. Wendell, Associate Professor of Biological Sciences and Genetics at Oakland University.
Both Dr. Hartrick and Dr. Wendell stressed that developing pain strategies requires studying a vast array of factors, some of which are at least partially influenced by a person’s genetic makeup.
“While this study did not confirm an association between anxiety and COMT type, such an association could explain the apparent paradox in our findings and thus may represent an important confounder affecting pain assessments and pain studies that examine the genetic role of COMT.”
Source: American Society of Anesthesiologists (www.asahq.org) press release, Oct 20, 2009, modified