Pauline Anderson

May 01, 2014

PHILADELPHIA — A new study provides important new insights into gene-driven perceptions of pain.

While the study won't have an immediate effect on treatment choices for chronic pain, it will help doctors understand why some patients feel more pain than others, said lead researcher, Tobore Onojighofia, MD, MPH, clinical affairs manager, Proove Biosciences, Irvine, California. "The analysis helps us to understand that genes play a vital role in pain perception."

It also provides an objective assessment of pain, he added. "Before this study, the most a doctor could do was ask patients subjectively where on a scale of 0 to 10 their pain lies."

Results of the study were presented here at the American Academy of Neurology (AAN) 66th Annual Meeting.

Pain Scale

The study included 2721 patients at 48 clinical sites in the United States who were prescribed opioids for chronic pain, mostly musculoskeletal and back pain.

Researchers genotyped these patients and evaluated several single-nucleotide polymorphisms.

The patients completed a pain visual analogue scale (VAS), rating their perception of pain intensity on a scale from 0 to 10. In this analysis, 249 patients (9.2%) reported low pain perception (a score of 1 to 3 on the VAS), while 1259 (46.2%) had moderate pain perception (4 to 6 on the scale) and 1213 (44.6%) had high pain perception (a score of 7 to 10).

The study excluded patients with no pain perception (0 on the scale). "It didn't make any sense to put people with no pain in the analysis because it was looking at genetics and pain," explained Dr. Onojjighofia.

One of the variants (DRD1) was more prevalent in the low pain perception group than in the high pain perception group (odds ratio [OR], 1.334 [P < .043]; positive predictive value [PPV], 84.44%).

Among the patients with moderate pain perception, 2 variants, COMT (OR, 1.25 [P < .007]; PPV, 52.41%) and OPRK (OR, 1.19 [P < .032]; PPV, 51.09%), were more prevalent than in those with high pain perception.

Among patients with high pain perception, the DRD2 variant was more prevalent than in patients with moderate pain perception (OR, 1.25 [P < .041]; PPV, 52.61%).

Sex Difference

The analysis showed that women were more likely than men to have high pain perception, and that men were more likely to have low pain perception. The duration of opioid use did not affect the analysis, said Dr. Onojighofia.

"This analysis is going to help doctors improve pain management," commented Dr. Onojighofia. "A doctor can view this information as an objective guidepost to better interpret a patient's perception of their pain."

"It puts things into perspective and puts objectivity into it," he added. "A doctor can run a test and say, okay this patient is not actually lying about being in pain, that the patient is genetically predisposed to having a higher perception of pain."

A genetic test might be in order when a patient reports having a lot of pain when most people with the same condition would not be experiencing such pain, said Dr. Onojighofia.

As an example, he used a hypothetical patient whose pain doesn't go away as it normally would with a nonsteroidal anti-inflammatory drug. In this case, testing might indicate the presence of certain genes that are causing that person to have a higher pain perception.

American Academy of Neurology (AAN) 66th Annual Meeting. Abstract P4.349. Presented April 30, 2014.

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