A problem for clinicians treating patients with fibromyalgia syndrome (FM) is that they often are not equipped with effective methods to assess fatigue, and without dependable ways to measure fatigue, it's difficult to evaluate treatment efficacy. However, according to a research article published in the journal Arthritis Research & Therapy, persons with Fibromyalgia syndrome can be categorized in four clusters respectively sharing similar symptom profiles, using the Outcome Measures in Rheumatology (OMERACT) core symptom domains. The Open Access paper, entitled: "OMERACT-based fibromyalgia symptom subgroups: an exploratory cluster analysis" is coauthored by corresponding author Ann Vincent and Mary O. Whipple of the Division of General Internal Medicine at the Mayo Clinic in Rochester, Minnesota; Tanya L. Hoskin of the Mayo Clinic Division of Biomedical Statistics and Informatics; Daniel J. Clauw and David A. Williams of the University of Michigan's Health System Chronic Pain and Fatigue Research Center in Ann Arbor; Debra L. Barton of the Mayo Clinic Division of Medical Oncology; and Roberto P. Benzo of the Mayo Clinic Division of Pulmonary and Critical Care Medicine. A particular research interest of Dr. Ann Vincent, M.B.B.S., M.D.,, a junior investigator and consultant in the Mayo Clinic's Division of General Internal Medicine in Rochester, Minnesota, and medical director of the Fibromyalgia and Chronic Fatigue Clinic, is fatigue as it relates to fibromyalgia, which is estimated to afflict from three to six million people in the United States alone, with fatigue cited as a symptom by about three-quarters of FM patients, and on finding better ways to evaluate and treat fatigue in fibromyalgia. "Not much is known about fatigue related to fibromyalgia,"