Study Identifies Three Distinct Subgroups of Fibromyalgia

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By Mindy Hung

Oct. 3, 2003 — Researchers have identified three distinct subgroups of patients with fibromyalgia (FM), according to results published in the October issue of Arthritis & Rheumatism.

"There appears to be a group of fibromyalgia patients who exhibit extreme tenderness but lack any associated psychological/cognitive factors, an intermediate group who display moderate tenderness and have normal mood, and a group in whom mood and cognitive factors may be significantly influencing the symptom report," write Thorsten Giesecke, MD, and colleagues from the University of Michigan, in Ann Arbor.

"Previous attempts at identifying subsets have been based solely on psychological and cognitive features. In this study, we attempt to identify patient subsets by incorporating these features as well as the degree of hyperalgesia/tenderness, which is a key neurobiologic feature of this disease," they add.

Investigators recruited and screened 117 patients (102 women and 15 men), ages 18 to 60 years, who met the 1990 American College of Rheumatology criteria for the classification of FM.

Researchers excluded those with severe physical impairment; medical conditions capable of causing patients' symptoms; cardiopulmonary disorders; uncontrolled endocrine or allergic disorders; malignancy; severe psychiatric illness; factors known to affect the hypothalamic-pituitary-adrenal axis (such as cigarette smoking or high daily caffeine intake); and usage of medications other than as-needed analgesics and appropriate dosages of thyroid hormone.

Subjects taking part in the two-day study protocol were asked to discontinue intake of antidepressants within one week prior to the study, and they were allowed to take nonsteroidal anti-inflammatory drugs until three days before the trial.

On the first day of study, patients completed self-report questionnaires from several domains consisting of mood, evaluated by the Center for Epidemiologic Studies Depression Scale and the State-Trait Personality Inventory; and cognition, evaluated by the catastrophic and control of pain subscales of the Coping Strategies Questionnaire. On the second day of the study, investigators tested for hyperalgesia/tenderness by dolorimetry and random pressure-pain applied at suprathreshold values.

All screened patients completed the study protocol; however, investigators obtained complete data on 97 of the 117 patients (85 women [87.6%] and 12 men [12.4%]).

Cluster analytic procedures revealed three subgroups of FM patients. Multivariate analysis of variance (ANOVA) confirmed that each variable was differentiated by the cluster solution (Wilks' [degrees of freedom, 6,89] = 0.123; P < .0001), with univariate ANOVAs also indicating significant differences (all P < .05).

The largest subgroup, which consisted of 55 patients (57%), showed moderate mood rating, moderate levels of catastrophizing and perceived control over pain, and low levels of tenderness. A second subgroup of 31 patients (32%) demonstrated significantly elevated values on the mood assessments, the highest values on the catastrophizing subscale, the lowest values for perceived control over pain, and high levels of tenderness.

The final group, of 16 patients (16%), displayed normal mood ratings, low levels of catastrophizing, the highest level of perceived control over pain, and extreme tenderness on evoked-pain testing.

"It might be expected that cluster 1, in which patients had moderate mood difficulties and already had very adaptive cognitive factors may be less likely to need or respond to cognitive behavioral approaches, whereas cluster 2, in which patients had extremely high levels of distress, might benefit most from this type of program," investigators write.

"Cluster 3 may possibly respond best to symptom-based pharmacologic therapy, including antidepressant agents with analgesic properties. Further studies need to replicate these findings, and additional testing should be done to determine whether these FM subgroupings can, in fact, be used to identify optimal treatments," they add.
This research was supported by a Department of Army grant, and by the National Institutes of Health.

Reference: Arthritis Rheum. 2003;48:2916-2922
Reviewed by Gary D. Vogin, MD
Source: Medscape.

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