Fibromyalgia Subgroups Identified Using Model-Based Clustering: Results from UK Biobank.

Fibromyalgia (FM) is a heterogeneous chronic condition with wide variability in symptom burden, psychosocial distress, and functional impact. This study aimed to identify latent FM subgroups reflecting multidimensional patient profiles using comprehensive biopsychosocial variables and model-based clustering methods within UK Biobank. Individuals meeting the 2016 American College of Rheumatology FM criteria (n = 4,172) were analysed using Gaussian mixture clustering. Twenty-eight variables across sociodemographic, clinical symptoms, and psychological/behavioural domains were included. Cluster stability was evaluated using bootstrap resampling and adjusted Rand indices (ARI). Variable importance was assessed using Random Forest analysis. Three distinct subgroups were identified: the Resilient Majority (62.3%) with low symptoms and psychological resilience; the Severe Phenotype (20.1%) with pronounced pain, fatigue, and psychological distress; and the Socially Vulnerable Minority (17.6%) characterized by ethnic diversity, rural residence, and social isolation. Sociodemographic and psychological/behavioural variables (e.g. frequency of feeling down, home area population density, ethnicity, frequency of home visits, and smoking status) demonstrated greater discriminative contribution than clinical symptom variables. All clusters demonstrated high stability (ARI > 0.93). These findings identify subgroups within FM defined not only by symptom severity but also by structural vulnerabilities and psychosocial factors. Recognizing such heterogeneity has implications for developing stratified, equitable management approaches that integrate psychosocial dimensions alongside clinical symptoms. PERSPECTIVE: Three fibromyalgia subgroups were identified: a resilient majority, a severe phenotype with socioeconomic disadvantage, and a socially vulnerable minority characterized by ethnic diversity and rural isolation patterns. Psychosocial factors outperformed clinical symptoms in discriminating subgroups, underscoring the need for stratified and patient-centred management addressing the biopsychosocial complexity of fibromyalgia.