Somatization, psychological distress, and quality of life across fibromyalgia, irritable bowel syndrome, and their comorbid phenotype: a cross-sectional clinical comparison

Laura Prospero¹Giuseppe Riezzo¹Gaetana Laselva²BENEDETTA D'ATTOMA¹Antonia Ignazzi¹Francesco Goscilo¹Antonella Bianco³Isabella Franco³Nicola Verrelli³Claudia Beatrice Bagnato³Sergio Coletta⁴Maria Grazia Refolo⁵Francesco Russo^1*

• ¹Functional Gastrointestinal Disorders Research Group, IRCCS "Saverio de Bellis", Castellana Grotte, Italy
• ²Rheumatology Outpatient Clinic, IRCCS "Saverio de Bellis", Castellana Grotte, Italy
• ³Laboratory of Movement and Wellness, IRCCS "Saverio de Bellis", Castellana Grotte, Italy
• ⁴Core Facility Biobank, IRCCS "Saverio de Bellis", Castellana Grotte, Italy
• ⁵Laboratory of Clinical Pathology, IRCCS "Saverio de Bellis", Castellana Grotte, Italy

Background: Fibromyalgia (FM) and irritable bowel syndrome (IBS) are increasingly recognized as disorders involving central sensory processing and gut–brain axis dysregulation, often accompanied by autonomic and psychological disturbances. Methods: We investigated whether patients with comorbid FM and IBS (FM+IBS) experience greater somatization and reduced quality of life (QoL) compared to those with either condition alone, and if somatization serves as a predictor of gastrointestinal (GI) symptom severity. In this cross-sectional study, 53 adults (mean age 47.4 ± 1.3 years; 48 women) were classified into three groups: FM-only (n = 13), IBS-only (n = 18), and FM+IBS (n = 22). Participants completed validated assessments including the IBS Symptom Severity Scale, the Symptom Checklist-90-Revised, the Perceived Stress Scale, and QoL measures (SF-36, WHOQOL-BREF). Group differences were analyzed using the Kruskal-Wallis test, and predictors of IBS severity were identified via stepwise multiple linear regression. Results: FM-only and FM+IBS patients reported similar levels of pain, fatigue, and functional impact. GI symptoms were mild in FM-only patients but moderate in IBS-only and FM+IBS groups, with large effect sizes for psychological distress, mental health, and IBS severity. While FM+IBS participants showed slightly higher FM-related symptom scores, differences were not statistically significant. Somatization and diagnostic group independently predicted IBS severity, together explaining 50% of the variance. Conclusion: These findings demonstrate a progressive increase in somatization and a parallel decline in QoL across the spectrum from IBS-only to FM-only to FM+IBS, supporting the concept of functional somatic syndromes as a continuum. Incorporating routine assessment of somatization and QoL impairment may help identify patients at higher risk of treatment resistance and facilitate timely, integrated biopsychosocial strategies, including cognitive-behavioral and neuromodulatory interventions.