Symptoms expressed by patients with fibromyalgia may align with one of two distinct subclusters, and further study may lead to personalized treatments, according to a recently published analysis.
Researchers enrolled 120 patients with fibromyalgia (108 women) into a prospective, longitudinal, observational study. Patients met 1990 American College of Rheumatology (ACR) criteria and received a variety of therapeutic interventions from community physicians at the time of enrollment.
Structural equation modeling was used to analyze the data and to identify the number of distinct subclusters present. Two distinct subclusters were identified and included similar proportions of men in each group. Both subclusters were similar in age, BMI, daytime sleepiness, and self-perceived cognitive dysfunction on attention/concentration, verbal memory, visual-perceptual ability and visual-spatial memory subcategories. Patients in subcluster 1 reported more intense symptoms than patients in subcluster 2, including higher widespread pain index (WPI) scores, more tender points and a lower pain threshold on dolorimetry.
Discriminant function analysis showed the two subclusters were distinct and varied by widespread pain and somatic symptoms. Patients in subcluster 1 were more likely to have higher widespread pain, unrefreshed sleep and somatic symptoms, while patients in subcluster 2 had more fatigue and cognitive symptoms with pain that was less widespread and not as intense.
The 2010 ACR fibromyalgia diagnostic criteria was met by 94% of patients in subcluster 1, while 42% of patients in subcluster 2 met this criteria. No patients in subcluster 1 met 2010 ACR criteria for having both a WPI score of 3 to 6 or a symptom severity scale score of 9 or greater. Patients met only the 1990 ACR criteria by 6% in subcluster 1 and by 35% in subcluster 2, with significant tenderness present in the absence of widespread pain.
“These clusters provide further evidence that [fibromyalgia syndrome] FMS is best considered an illness of polysymptomatic distress rather than a primary pain disorder,” the researchers wrote. They further concluded, “The observation that 35% of the subjects in subcluster 2 did not meet the 2010 FMS diagnostic criteria indicates that the 2010 FMS diagnostic criteria is most sensitive in capturing moderate to severe widespread pain symptoms. These results also demonstrate that a minority of persons can demonstrate the substantial widespread tenderness, as indicated by meeting the 1990 ACR criteria, despite not having substantial widespread pain within the last week. While there is a close relationship between clinical pain reporting and tenderness, it is not absolute.” – by Shirley Pulawski
Disclosure: The researchers report that the study was funded by Medstar Research Institute (grant NCT00888563) and the Division of Intramural Research of the National Institute of Nursing Research.