A study of electronic medical records that analyzed over 11,000 patient-reported pain scores has found that women consistently report higher pain scores than men for a number of diseases. The work, from David Ruau and colleagues at Stanford University School of Medicine, Stanford, California, US, mined a large trove of clinical data to shed new light on the longstanding question of whether there are significant differences in how males and females experience pain.
“We hope that this research will settle once and for all that differences in reported pain exist between men and women,” Ruau wrote in an e-mail to PRF.
The work was published January 13 online in the Journal of Pain.
The end of an endless debate?
Up until now, there has been no clear answer to the question of whether there are sex differences in pain perception. A recent literature review from Manon Choinière of the University of Montreal, Quebec, Canada, and others looked at 122 laboratory studies published between 1998 and 2008 on sex differences in pain sensitivity, and reached that conclusion (Racine et al., 2011). But studies so far do show a clear trend, says Jeffrey Mogil, of McGill University, Montreal, Quebec, Canada. “Not every study finds a difference, but when it does, it is always in the same direction: that women are more sensitive to pain,” said Mogil, who studies sex differences in pain perception and was not involved with the review or the new study.
In the new research, Ruau and coworkers collected de-identified electronic medical records from 72,773 unique patients in the Stanford Hospital and Clinics and the Lucile Packard Children’s Hospital, for which they obtained demographic and encounter-specific information. A total of 161,827 patient-reported pain scores that used a 1-10 numerical pain scale was obtained. Children were excluded from the dataset. The authors used the first pain record registered for each patient, and only those records that included a primary diagnosis and at least one recorded pain score. The authors further filtered the dataset by 47 different diseases, each having at least 41 encounters for both men and women, which led to a final dataset of over 11,000 patients.
Their results show average pain scores for women are significantly higher than those of men. For some diagnoses, the difference was greater than one point on the scale, which is clinically significant. Furthermore, the authors show the actual differences in pain scores for each of the 47 diseases they analyzed, all of which showed higher scores in women.
The size of the dataset also allowed the investigators to ask which diseases most commonly produce gender differences in reported pain. After excluding diagnoses with a minimum number of encounters, disorders of the musculoskeletal, circulatory, respiratory, and digestive systems showed up at the top of the list. This study also found differences in conditions never before reported, such as acute inflammatory sinusitis.
This study provides well-supported and convincing evidence that there are differences in pain perception between men and women, and this should end the debate, once and for all, said Mogil. “With a sample size of 11,000, even a small difference shows up clearly. We don’t know exactly why, but I hope we will stop arguing now whether there is or is not a difference in pain sensitivity or in pain rating…there is.”
There are some caveats to the study. It is not known whether patients had taken over-the-counter analgesics just before their pain assessment. There are also sociocultural and psychological factors that can affect reported pain scores. For example, Ruau and coauthors point out that patients may report different pain levels based on the gender of the physician evaluating them. The medical records do not report the sex of the doctor, which could introduce some bias, but such variables are likely random and thus are taken into account over the complete dataset.
Future work
The present study also has room for more analyses, since it looked not only at male and female patients, but also at a wide variety of diseases, over a wide number of variables including ethnicity, socioeconomic background, and others. Filtering for different variables will provide more insights about differences not only in pain perception, but also in physiological values, medications, vital signs, and others.
This study should serve as an example for future studies designed to gain insight into population-wide trends as well as group comparisons, and not just for pain research, but for virtually any medical condition.
Now that the issue of whether there are clinical differences between the sexes is put to rest, researchers can focus on more interesting questions, such as the biological basis for sex differences in the perception or experience of pain. Choinière and colleagues, in a second review, analyzed 10 years of work on biological, social, and psychological factors that alter pain sensitivity between men and women, and found a picture that is both incomplete and exceedingly complex (Racine et al., 2012). Involvement of hormonal and physiological factors showed inconsistent results, as did psychological factors such as depression or anxiety. Only cognitive and social factors explained some sex-related differences, whereas past individual history seems influential in female pain responses.
Clearly, more research is needed, and fortunately, sex differences is an area that is getting more attention recently. For some of the latest work on this topic, see the PRF coverage of Neuroscience 2011.
Karl Gruber is a Ph.D. candidate in genetics at Heinrich Heine University in Düsseldorf, Germany, and a freelance science writer.