Wednesday, June 5, 2013
Dutch researchers report that weather conditions including temperature, sunshine, and precipitation appear to have no impact on fibromyalgia symptoms of pain or fatigue in female patients [Bossema et al. 2013]. However, study results published in Arthritis Care & Research, a journal of the American College of Rheumatology (ACR), do allow that some individual patients still may be sensitive to changes in the weather. What can or should be done about this is an unanswered question.
Some evidence suggests that fibromyalgia syndrome, or FMS, affects 2% of the world population, with a greater prevalence among women. In the United States, it is estimated that 5 million people experience the widespread pain, fatigue, headaches, and sleep disturbances associated with this chronic pain syndrome. While causes of FMS remain unknown, studies suggest that many patients have increased sensitivity to a range of stimuli and up to 92% claim that weather conditions worsen their symptoms.
“Many fibromyalgia patients report that certain weather conditions seem to aggravate their symptoms,” explains first author, Ercolie Bossema, PhD from Utrecht University in the Netherlands, in a news release. “Previous research has investigated weather conditions and changes in fibromyalgia symptoms, but an association remains unclear.”
To further explore the impact of weather on pain and fatigue in FMS, the research team enrolled 333 female patients with FMS in a prospective observational study. Participants had a mean age of 47 years and a diagnosis of fibromyalgia for 3.5 years on average. Information was gathered during July through December 2006 and each patient completed a daily diary during a single 28-day period to record their pain and fatigue symptoms, as well as depressed mood, sleep quality, and physical activity. At the same time, researchers obtained from the Royal Netherlands Meteorological Institute air temperature, sunshine duration, precipitation, atmospheric pressure, and relative humidity data covering the study period.
Multilevel regression techniques were used to conduct 50 analyses, which variously compared 5 weather variables with 2 FMS symptoms (pain and fatigue) with 5 other variables (eg, demographics, season, etc.). Results indicated the following:
- In total, data across all patients and days showed moderate levels of pain (mean=3.35) and fatigue (mean=3.77) on 5-point scales, and the 2 symptom measures were highly correlated.
- In 5 of the 50 analyses (10%), weather variables demonstrated statistically significant but small effects on pain or fatigue symptoms among all patients. For example, on 1-to-5 scales, each hour of increased sunshine was associated with 0.005 units lower pain. Each degree increase in air temperature was associated with 0.01 units greater fatigue, while each 1% increase in relative humidity resulted in a 0.004 unit decrease in fatigue. These were not clinically significant changes.
- A second analysis examined whether there were differences between patients in their responses to weather. In 10 of 50 analyses (20%), the researchers found statistically significant but small differences between patients’ responses to weather, suggesting pain and fatigue symptoms were differentially but inconsistently impacted by some weather conditions; eg, greater pain with either lower or higher atmospheric pressure.
- Overall, for each combination of weather variable and symptom (pain, fatigue) there appeared to be no relationship in a third of the patients, there was a negative relationship in another third of the patients, and a positive relationship in the remaining third. Thus, while some of the comparisons were statistically significant, there essentially was a cancelling-out of effects across the aggregate sample of patients.
The researchers conclude that differences in individual symptom responses to weather conditions did not appear to be associated with any specific demographic variables, functional or mental health status, nor seasonal- or weather-related variations. Therefore, the analyses provide more evidence against, than in support of, the daily influence of weather on FMS-related pain and fatigue in female patients. However, they stress that the findings do not rule out the possibility of relationships between weather and symptoms in individual patients.
This is the largest study to date that has investigated the impact of weather on FMS symptoms, and it is disappointing that there was no association overall between specific patient characteristics and weather sensitivity. This is especially important because, as the researchers themselves note, a vast majority of persons with FMS do claim that weather conditions have an effect on their pain, fatigue, and other symptoms.
From an evidence-based perspective, this is an interesting example of how, given a sufficiently large sample and abundant data, there can be statistically significant associations observed (in terms of p-values), but heterogeneity in the data produces only small, inconsistent, and/or clinically unimportant absolute effect sizes. For example, to a small degree patients differed from each other on certain variables, but in opposite directions — eg, some found changes in temperature increased their pain while the same temperature changes decreased pain in others. In both cases, however, the weather did have an impact that may have been clinically meaningful for the individual patients.
There are many potentially confounding factors in a study such as this, some of which the researchers discuss. For one thing, the patients — who were monitoring and recording their symptoms on a daily basis — may have paid more attention than usual to changes in both symptoms and the weather. This sort of heightened perception or “attention bias” may have influenced responses, as well as a “confirmation bias” among those who believed at the outset that weather affected their symptoms, whether or not this was actually the case.
The researchers also observe that a number of patients spent a majority of their days indoors, which might have diminished effects of outside weather conditions. Additionally, most patients participated in the study during autumn, rather than summer or winter months, which could have influenced the sort of weather to which they were exposed; although, the researchers tried to statistically control for this.
While the average time since FMS diagnosis in all subjects was 3.5 years, there was a wide range of <1 to 45 years. Furthermore, there was a diversity of comorbid conditions among subjects that might have influenced their symptoms; eg, 14% had a rheumatic condition, 10% lung disease, 17% mental health problems, 42% other (including, endocrine disorder, chronic fatigue syndrome, etc.). This sort of medical heterogeneity makes it difficult to distinguish symptoms solely attributable to FMS and the influences of specific weather variables.
In sum, it seems that this study is largely uninformative in helping to identify those patients with FMS who are most likely to be sensitive to weather conditions, and the direction or severity of the effects in those who are sensitive. Perhaps, the best conclusion is that women with FMS differ in so many ways when it comes to the potential influence of weather on their symptoms that it makes no significant difference from an overall clinical perspective.
Bossema and colleagues suggest that further research should include larger samples and encompass more patient characteristics — such as personality traits, beliefs about chronic pain, and attitudes regarding the influence of weather on symptoms — to help explain individual differences in weather sensitivity and its impact on FMS-related pain and fatigue. But, the question still remains: Even if individual differences are determined, what are practitioners and patients supposed to do about them to help better manage FMS symptoms?
REFERENCE: Bossema ER, van Middendorp H, Jacobs JWG, et al. The Influence of Weather on Daily Symptoms of Pain and Fatigue in Female Patients with Fibromyalgia: A Multilevel Regression Analysis. Arthritis Care and Research. 2013(Jun); online ahead of print [abstract here].
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