Irritable bowel syndrome is related to small fibre pathology in patients with fibromyalgia.

OBJECTIVES

Fibromyalgia (FM) is a multisystem disorder frequently associated with functional gastrointestinal disorders, particularly irritable bowel syndrome (IBS). Diet-related factors and gut microbiota alterations, key elements in IBS pathophysiology, may disrupt the gut-brain axis, promoting immune activation, altered pain processing, and peripheral nerve dysfunction, including small fibre involvement, which has been consistently reported in FM. The study investigated whether IBS symptom severity in FM is associated with clinical and psychological features and with neuropathological evidence of small fibre involvement.

METHODS

In this monocentric cross-sectional observational study, 89 FM patients underwent clinical and psychological assessments. IBS severity was assessed using the IBS Severity Scoring System (IBS-SSS). Skin biopsy with quantification of intraepidermal nerve fibre density (IENFD) at proximal and distal sites was performed in 57 patients. Patients were classified into mild-moderate and severe IBS groups. Between-group differences were analysed using Mann-Whitney U and χ² tests. Spearman's rank correlation served to assess associations between IBS severity, clinical variables, and IENFD.

RESULTS

Severe IBS symptoms were present in 47.1% of patients. Compared with patients with mild-moderate IBS, those with severe IBS showed higher widespread pain index (WPI) and symptom severity scale (SSS) scores, indicating greater fibromyalgia severity, as well as increased anxiety and depressive symptoms, reduced sleep duration, and greater functional impairment (all p<0.05 after FDR correction). Skin biopsy revealed a higher prevalence of reduced IENFD, particularly at proximal sites, in severe IBS patients. Notably, IBS-SSS scores were negatively correlated with proximal IENFD (r=-0.34, p=0.01).

CONCLUSIONS

IBS severity identifies a clinically more severe FM phenotype with small fibre pathology. These findings are consistent with a possible interaction between gastrointestinal dysfunction and peripheral nerve involvement in FM, although mechanistic pathways require further investigation.