Symptoms reported by patients with fibromyalgia may belong to one of two distinct subclusters, possibly leading to personalized treatments, according to an analysis recently published in the journal Arthritis Care & Research titled “Understanding the Association of Fatigue With Other Symptoms of Fibromyalgia: Development of a Cluster Model.”
Fibromyalgia syndrome (FMS) is characterized by widespread chronic pain, profound fatigue, and sleep disturbance. It appears to represent the end of the spectrum of polysymptomatic distress. Estimates indicated that FMS affects 6 percent of the U.S. population. In some patients with fibromyalgia, fatigue interferes with the performance of daily activities as much as or more than bodily pain.
Because most studies have primarily investigated the mechanisms and treatment of FMS-related pain, less is known about other symptoms, including fatigue.
To develop a symptom cluster model that could describe factors of fibromyalgia associated with fatigue severity and to explore FMS’s clinical symptom subclusters based on the varying intensity of symptoms, Nada Lukkahatai at the School of Nursing, University of Nevada at Las Vegas, and colleagues enrolled 120 patients with fibromyalgia (108 of whom were women) into a prospective observational study. Patients met 1990 American College of Rheumatology (ACR) criteria and were receiving a variety of therapeutic interventions from doctors at the time of enrollment.
All patients enrolled in the study were asked to complete questionnaires assessing fatigue, pain, depression, anxiety, pain catastrophizing, daytime sleepiness, cognitive function, and fibromyalgia-related polysymptoms.
The results revealed that fibromyalgia fatigue was associated with widespread pain, symptom severity, pain intensity, pain interference, cognitive dysfunction, catastrophizing, anxiety, and depression.
Two distinct clinical symptom subclusters emerged: subcluster 1 (78 percent of the study patients), defined by widespread pain, unrefreshed waking, and somatic symptoms; and subcluster 2 (22 percent of participants), defined by fatigue and cognitive dysfunction, with pain being a less severe and less widespread occurrence.
The 2010 ACR fibromyalgia diagnostic criteria was met by 94 percent of patients in subcluster 1, while 42 percent of patients in subcluster 2 met this criteria. No patients in subcluster 1 met 2010 ACR criteria for having both a widespread pain score of 3 to 6 or a symptom severity scale score of 9 or greater. Patients met only the 1990 ACR criteria by 6 percent in subcluster 1 and by 35 percent in subcluster 2, with significant tenderness present when there was no widespread pain reported.
“These clusters provide further evidence that FMS is best considered an illness of polysymptomatic distress rather than a primary pain disorder,” the researchers wrote, according to a news release. “The observation that 35 percent of the subjects in subcluster 2 did not meet the 2010 FMS diagnostic criteria indicates that the … 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,” the authors said.
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