After knee or hip replacement surgery, fibromyalgia symptoms ease markedly in some patients but not in all, suggesting important patient-to-patient differences in how those symptoms develop, a recent study says.
The findings were published in the journal Rheumatology in the paper, “Top down or bottom up? An observational investigation of improvement in fibromyalgia symptoms following hip and knee replacement.”
Osteoarthritis (OA) is the most common form of arthritis; it occurs when the cartilage that cushions the bones at a joint wears away, so bones grind against each other. When this occurs in the hips or knees, replacement surgeries can restore functionality and reduce pain over time.
It’s widely agreed that many people with OA also experience symptoms of fibromyalgia, including pain and fatigue. In this study, researchers wondered how these fibromyalgia symptoms would change — or not — following joint replacement surgery.
They recruited 150 individuals with OA who were undergoing either hip or knee replacement and who had a score of four or higher on the 2011 Fibromyalgia Survey Criteria, which measures both widespread pain and symptom severity in fibromyalgia.
These people were followed over time, during which the researchers classified them into one of two groups: 102 were in the “Improve” group, and the remaining 48 into the “Worsen/Same” group. As the names suggest, patients in the Improve group experienced a significant decrease in fibromyalgia symptoms following the surgery; those in the Worsen/Same group didn’t.
The researchers noted that people in the Worsen/Same group were significantly more likely to have higher survey scores and more severe pain at the surgical site prior to surgery, as well as to higher fatigue and depression scores. Other factors (age, sex, sleep patterns, physical function, etc.) were not significantly linked with either group.
What the researchers focused on is the very fact that there were two significantly distinct groups.
Two basic models for how fibromyalgia pain originates exist. In the “bottom-up” model, there is a pain-inducing stimulus (e.g., inflammation) somewhere in the body, and this sends a pain signal to the brain. In the “top-down” model, the brain senses pain without there being an active stimulus.
Thus, the distinction between the two above groups can be explained with the idea of different patients experiencing different forms of fibromyalgia: in the Improve group, the surgery removed the painful stimulus (joint inflammation), and without that stimulus, related fibromyalgia pain decreased substantially, suggestive of the “bottom-up” model. In contrast, symptoms in the Worsen/Same group didn’t get better even after the painful stimulus was removed because it wasn’t directly linked to a stimulus, suggesting “top-down” pain.
This suggests that patients with apparently similar fibromyalgia symptoms will respond very differently to interventions like surgery, or even medications aimed at reducing brain-perceived pain in the “top-down” model. This also raises an obvious question: how can doctors tell the difference before giving treatment that might not be effective?
Well, the above differences — depression, fatigue, etc. — might be a place to start. But, as the researchers noted, “these differences were modest and do not appear to lend themselves to forming reliable cut-offs.” Applying them in practice, in other words, is unlikely.
Instead, the researchers suggest that people whose fibromyalgia is accompanied by mood disorders and/or by heightened sensitivity to normally non-painful stimuli (like light and sound) may be more likely to have “top-down” fibromyalgia — which may be, at least, a jumping-off point for future research that could lead to better and more patient-specific care.
“Future studies will determine whether and how these patterns hold in other surgical cohorts with high levels of comorbid FM symptoms,” the scientists concluded.