Thursday, February 16, 2012

Fibromyalgia & Obesity: Enough Already!

Obesity & Pain Excess body weight may incur many health problems and research has linked obesity with various chronic pain conditions, including fibromyalgia syndrome (FMS). A new report furthers the notion that obesity in persons with FMS may be associated with greater disability and poorer quality of life. However, the implied causal relationship between obesity and FMS is uncertain and there is a possibility that this whole line of investigation may be wrong-headed and unhelpful.

In the latest iteration of research establishing fibromyalgia-obesity linkages, a team from the Mayo Clinic, Rochester, Minnesota, assessed Body Mass Index (BMI) status and its association with symptom severity and quality of life [Kim et al. 2012]. In this study, 888 patients with FMS who were seen at a Fibromyalgia Treatment Clinic completed the Fibromyalgia Impact Questionnaire (FIQ) and the Short Form 36 (SF-36) health survey.

Writing in the February 2012 edition of Arthritis Care & Research, the researchers report that the BMI distribution of nonobese (BMI <25.0), overweight (BMI 25.0–29.9), moderately obese (BMI 30.0–34.9), and severely obese (BMI ≥35.0) patients with FMS was roughly 28%, 27%, 22%, and 23%, respectively. That is, 45% of the participants with FMS could be characterized as obese.

Age was significantly different across the 4 groups, with those having a greater BMI being older (P = 0.004). However, after adjusting for age, patients with higher BMI scores still had more FMS-related symptoms with worse total FIQ scores (P < 0.001), as well as significantly worse scores in the FIQ subscales of physical function, work missed, job ability, pain, stiffness, and depression. Furthermore, heavier patients also had significantly poorer SF-36 scores in physical functioning, pain index, general health perception, and other factors. Post hoc analyses of the 4 groups showed that differences between groups resided primarily in the severely obese group compared with the other groups.

The researchers conclude that obesity, especially severe forms, incurs higher levels of FMS symptoms and a lower quality of life. They suggest that their “results underscore the importance of incorporating weight management strategies in treatment programs for fibromyalgia patients.”

COMMENTARY: Unfortunately, this research is actually not entirely new, offers few insights, and the weight-loss recommendation has little evidentiary support.

For one thing, ample evidence already suggests that obesity and pain often go together. For example, a prior Pain-Topics UPDATE [here] noted that obesity appears to play a critical role in arthritis: in one study, roughly 30% of obese adults had been diagnosed with arthritis compared with 20% of persons categorized as overweight and only 17% in adults of normal or lower-than-normal weight. Recently, we also reported on a large study of more than 1-million Americans that confirmed the presence of higher rates of pain among the heaviest of individuals [UPDATE here].

Furthermore, prior UPDATES have observed that FMS — characterized by widespread pain and a range of functional disturbances — afflicts an estimated 10 million persons in the United States and up to 6% of the world population; most frequently women. Various research studies [eg, UPDATES here and here] have reported that overweight and obese women — particularly those who do not exercise — seem to be at higher risk of having FMS.

So, we get it. When it comes to pain… obesity is bad… and fibromyalgia is bad. But are FMS and obesity directly interconnected?

If so, will losing excess weight improve FMS and boost sufferers’ quality of life? Or, is all of this a cause-effect fallacy so common in pain research, called cum hoc, ergo propter hoc, or “with this, therefore because of this.” It presumes that conditions occurring together likely cause each other, which often is entirely erroneous.

It is well known that correlation is not the same as causation, yet much of the research implies that the strong associations of obesity and FMS do reflect some sort of cause-effect relationship. This sort of fallacious thinking is like the observation that significantly greater numbers of people always seem to be carrying umbrellas on days when it rains; therefore, umbrellas must be an important cause of rain. While this may seem absurd, somewhat of the same reasoning appears in the pain research literature.

For example, as we discussed in an UPDATE more than a year ago [here], a research team from Norway concluded from a large, retrospective, longitudinal study of women that being overweight or obese significantly increases their chances of developing fibromyalgia. Heavier women were reported to have up to a 70% higher risk of developing the disorder compared with women of normal weight. However, neither this study nor other research to date has tried to determine which condition, obesity or FMS, developed first. Therefore, they could not begin to determine cause and effect, even though some researchers and media reports have implied that being fat leads to FMS and/or makes it worse.

It seems equally plausible that FMS is more of a risk factor for excess weight than the reverse. The nature of the disease — with its physical discomforts, emotional stresses, and sleep disturbances — along with some of the medications used in its treatment may all predispose a person to weight gain, whether due to exercise avoidance, poor nutrition, or other influences. And, BMI is an inadequate measure for assessing cause-effect to begin with, since it does not account for many variables that could be important, such as location of body fat, muscle mass, bone structure, and a host of individual neurobiologic, ethnic, genetic, and metabolic factors.

So, what does the research to date tell us? Not much — and it might be time to stop investing further effort, and space in medical journals, to merely demonstrate an obesity-FMS association.

Knowing that obesity and FMS occur together to a considerable extent is interesting but of no diagnostic, prognostic, or therapeutic value. There is currently no well-established scientific rationale for why obesity might cause FMS, or vice versa. And, while there might be probable cause to believe that a weight-loss program could help to alleviate FMS symptoms, there is no convincing body of evidence to date in support of that notion.

Of course, this is not to deny that weight reduction would benefit the overall health of any obese person, but the role of obesity specifically in FMS — physiologically and psychologically — needs much further elaboration to determine if treatment strategies for dealing with this aspect of FMS are necessary, appropriate, and beneficial.

REFERENCE: Kim C-H, Luedtke CA, Vincent A, et al. Association of body mass index with symptom severity and quality of life in patients with fibromyalgia. Arthritis Care & Research. 2012(Feb);64(2):222–228 [abstract here].