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Reconsidering the boundaries between fibromyalgia and post-traumatic stress disorder: evidence from label-free distributional similarity analysis in 2,470 participants
M. Luís1, A.M. Pinto2, F. Caramelo3, J.A.P. Da Silva4
- Rheumatology Department, Centro Hospitalar e Universitário de Coimbra; and Faculty of Medicine, University of Coimbra, Polo III, Polo das Ciências da Saúde, Coimbra, Portugal. maryanaluys@gmail.com
- Center for Research in Neuropsychology and Cognitive and Behavioral Intervention (CINEICC), Faculty of Psychology and Educational Sciences, University of Coimbra; and Psychological Medicine Institute, Faculty of Medicine, University of Coimbra, Portugal.
- Faculty of Medicine, University of Coimbra, Polo III, Polo das Ciências da Saúde, Coimbra, Portugal.
- Rheumatology Department, Centro Hospitalar e Universitário de Coimbra; Faculty of Medicine, University of Coimbra, Polo III, Polo das Ciências da Saúde, Coimbra; and Coimbra Institute for Clinical and Biomedical Research (i.CBR), Faculty of Medicine, University of Coimbra, Portugal.
CER20021
2026 Vol.44, N°6
PI 1159, PF 1168
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PMID: 42328947 [PubMed]
Received: 09/04/2026
Accepted : 19/05/2026
In Press: 22/06/2026
Published: 22/06/2026
Abstract
OBJECTIVES:
Fibromyalgia (FM) and post-traumatic stress disorder (PTSD) share key clinical features, including sleep disturbance, fatigue, cognitive symptoms and affect dysregulation, yet they are classified as distinct disorders. We examined whether FM and PTSD represent separable phenotypes or overlapping stress-related symptom profiles using a distributional similarity approach.
METHODS:
In an international cross-sectional online survey of adults aged 18–65 years, participants with a self-reported clinical diagnosis of FM or PTSD, and healthy controls, completed validated measures of somatic symptom burden, trauma-related symptoms, psychological vulnerability traits, comorbidities, and emotional activation patterns (EASEL-3). Case definitions were operationalised using established thresholds for polysymptomatic distress and PTSD symptom severity. To address unequal group sizes and reduce case-definition circularity, we applied adaptive sub-sampling with bootstrap resampling and quantified between-group similarity using Hellinger distance, complemented by stability analyses.
RESULTS:
Across somatic, psychological and affective domains (threat, drive and soothing systems), FM and PTSD showed substantial overlap with limited discriminatory capacity, while both differed clearly from healthy controls. Nearly half of participants meeting criteria for one condition also met criteria for the other, indicating high co-occurrence.
CONCLUSIONS:
These findings question the strict nosological separation of FM and PTSD and are compatible with a spectrum model of stress-related disorders. They further suggest that systematic trauma assessment and integrated, mechanism-based treatment strategies should be considered in the management of both conditions.
