The main objective of this study is to identify fibromyalgia syndrome (FMS) clusters using the Revised Fibromyalgia Impact Questionnaire (FIQR), and to examine whether the clusters differ in sociodemographic characteristics, clinical measures, direct and indirect costs, levels of inflammatory markers, and brain morphometry. A hierarchical cluster analysis was performed to classify a large, pooled Spanish sample of patients with FMS (N = 947) using the FIQR as clustering variable. A latent profile analysis was subsequently conducted to confirm the optimal number of FMS clusters. To examine external validity, a battery of clinical measures, economic costs, inflammatory markers, and gray matter volumes of relevant cortical and subcortical areas were analyzed. We also compared the discriminant validity of the clusters with the original FIQR severity categories. To promote the implementation in real-world clinical practice, we built a free online cluster calculator. Our findings indicated that a four-cluster solution more clearly captured the heterogeneity of FIQR data and provided the best fit. This cluster solution allowed for detection of differences for most clinical outcomes and economic costs. Regarding the inflammatory and brain-based biomarkers, differences were found in C-reactive protein, and tendencies were found in the right medial prefrontal cortex, the right parahippocampal gyrus, and the right middle cingulate cortex; brain regions associated with executive functions and pain processing. The original FIQR categories presented similar results, although their precision in discriminating among the nonextreme categories (ie, moderate and severe) was not sound. These findings are discussed in relation to previous research on FMS clustering.
A 4-cluster solution associated with different levels of severity was the most accurate classification for a large pooled sample of Spanish patients with fibromyalgia.
aGroup of Psychological Research in Fibromyalgia and Chronic Pain (AGORA), Institut de Recerca Sant Joan de Déu, Esplugues de Llobregat, Spain
bTeaching, Research and Innovation Unit, Parc Sanitari Sant Joan de Déu, Sant Boi de Llobregat, Spain
cPrimary Care Prevention and Health Promotion Research Network, RedIAPP, Madrid, Spain
dDepartment of Clinical Psychology and Psychobiology (Section Personality, Assessment and Psychological Treatments), University of Barcelona, Barcelona, Spain
eCerebral Imprints of Gender, Development and Pathology, Institut de Recerca Sant Joan de Déu, Esplugues de Llobregat, Spain
fCenter for Biomedical Research in Mental Health, CIBERSAM, Madrid, Spain
gDepartment of Health Psychology, Miguel Hernández University, Elche, Spain
hDepartment of Medicine and Surgery, Public Health, Psychology and Immunology and Medical Microbiology, Rey Juan Carlos University, Madrid, Spain
iInstituto de Neurociencias Federico Olóriz, Universidad de Granada, Armilla, Spain
jDivision of Neurology, The Hospital for Sick Children, Toronto, Canada
kDepartment of Psychiatry, Cruces University Hospital, Osakidetza-Basque Health System, BioCruces Health Research Institute, Barakaldo, Spain
lThe Institute of Neurosciences, University of Barcelona, Barcelona, Spain
Corresponding author. Address: Teaching, Research & Innovation Unit, Parc Sanitari Sant Joan de Déu, C/Dr Antoni Pujadas 42, 08830, Sant Boi de Llobregat, Barcelona, Spain. Tel.:+34 93 640 63 50 (Ext. 1-2540). E-mail address: email@example.com (A. Feliu-Soler).
Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.
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A. Pérez-Aranda and J.V. Luciano contributed equally to this work.
Received July 17, 2018
Received in revised form October 26, 2018
Accepted December 11, 2018