Identification of symptom and functional domains that fibromyalgia patients would like to see improved: a cluster analysis

Abstract

Background: The purpose of this study was to determine whether some of the clinical features of fibromyalgia (FM) that patients would like to see improved aggregate into definable clusters.

Methods: Seven hundred and eighty-eight patients with clinically confirmed FM and baseline pain > or =40 mm on a 100 mm visual analogue scale ranked 5 FM clinical features that the subjects would most like to see improved after treatment (one for each priority quintile) from a list of 20 developed during focus groups. For each subject, clinical features were transformed into vectors with rankings assigned values 1-5 (lowest to highest ranking). Logistic analysis was used to create a distance matrix and hierarchical cluster analysis was applied to identify cluster structure. The frequency of cluster selection was determined, and cluster importance was ranked using cluster scores derived from rankings of the clinical features. Multidimensional scaling was used to visualize and conceptualize cluster relationships.

Results: Six clinical features clusters were identified and named based on their key characteristics. In order of selection frequency, the clusters were Pain (90%; 4 clinical features), Fatigue (89%; 4 clinical features), Domestic (42%; 4 clinical features), Impairment (29%; 3 functions), Affective (21%; 3 clinical features), and Social (9%; 2 functional). The "Pain Cluster" was ranked of greatest importance by 54% of subjects, followed by Fatigue, which was given the highest ranking by 28% of subjects. Multidimensional scaling mapped these clusters to two dimensions: Status (bounded by Physical and Emotional domains), and Setting (bounded by Individual and Group interactions).

Conclusion: Common clinical features of FM could be grouped into 6 clusters (Pain, Fatigue, Domestic, Impairment, Affective, and Social) based on patient perception of relevance to treatment. Furthermore, these 6 clusters could be charted in the 2 dimensions of Status and Setting, thus providing a unique perspective for interpretation of FM symptomatology.

Trial registration: ClinicalTrials.gov NCT00333866.

Figure 1

Dendogram from the cluster analysis of the 20 clinical features. The dendrogram was generated using odds ratios (i.e. likelihood of pairs of symptoms being co-selected) as a proxy for distance between symptoms. A description of each clinical feature by number is presented in Table 1.

Figure 2

Multidimensional scaling map of the conceptual relationships among the clusters of clinical features. The conceptual map shows patient perceptions of the 20 clinical features divided into 6 distinct clusters on the dimensions of Setting, bounded by Group and Individual interactions on the vertical axis, and Status, bounded by Physical and Emotional domains on the horizontal axis. The items in each cluster were determined by the odds ratio of each item being co-selected by fibromyalgia patients as being important to their care. The relative location of each cluster identifies its dimensional relationship. For example, the Pain cluster would be considered strong with regard to Individual effects and the Physical domain, while the Domestic cluster would be strongly Group-related but would have roots in both Physical and Emotional domains.