0672: Determinants of Progressive Microstomia in Systemic Sclerosis: Insights from the GENISOS Cohort with a Focus on GI Involvement

Background/Purpose: Systemic sclerosis (SSc) is a complex autoimmune condition characterized by vascular abnormalities, immune dysregulation, and progressive fibrosis affecting both the skin and internal organs. Among its manifestations, facial and perioral involvement may lead to mouth opening reduction, known as microstomia, which negatively impacts nutrition, oral hygiene, and the tolerance of procedures like endoscopy or intubation. Despite its clinical impact, it remains unknown who will develop microstomia, and whether it is predictive of other SSc complications. This study aims to determine the evolution of microstomia over time, identify predictors of its progression, and explore its potential association with systemic manifestations of SSc.

Methods: We conducted a longitudinal analysis in the GENISOS cohort, including SSc patients with serial measurements of maximal mouth opening (MO), defined as the distance between the upper and lower lips. The percentage reduction in mouth opening was calculated from baseline to the minimum value recorded for each patient. Only patients with at least two observations separated by at least 6 months were included. Based on the distribution of MO percentage reduction values, a cut-off of 12.3% from baseline (top third of patients with the most significant MO change) was used a priori to define severe microstomia. Patients with a reduction >12.3% were classified as severe (group 2) and compared to those with a reduction < 12.3% (group 1). Clinical variables, including disease duration, skin involvement, and symptoms of internal organ dysfunction (e.g., dysphagia), were compared across groups. Logistic and Cox regression models were used to identify predictors of severely reduced MO.

Results: Patients with mild-to-moderate MO reduction (group 1) reached their lowest MO after a median of 0 months from baseline (IQR: 0.0-1.0), while those in the severe group (group 2) reached their lowest point after a median of 1.9 years (IQR: 0.9- 4.15). The severe group had a longer disease duration and a higher prevalence of facial telangiectasia and xerostomia. GI involvement was significantly more prevalent in group 2, with symptoms such as dysphagia, peptic ulcers, diarrhea, bloating, and malabsorption being particularly frequent (Table 1) (Figure 1). Multivariate analysis showed that longer disease duration (OR 1.2 per year; 95% CI 1.1–1.3) and GI Severity Score >1 (OR 2.7; 95% CI 1.1–6.5) were independently associated with severe reduction in MO. Cox regression confirmed that baseline GI involvement (GI Severity Score >1) predicted severe MO reduction ( >12.3%) (HR 2.3; 95% CI 1.8–3.0), with baseline dysphagia (HR:1.4; 95% CI 1.2–1.7) and/or diarrhea (HR:1.8; 95% CI 1.5–2.2) being the strongest predictors (Table 2).

Conclusion: Early GI symptoms—particularly dysphagia and diarrhea—were significantly associated with severe microstomia, suggesting that microstomia may serve as an external marker of progressive internal GI involvement. These findings highlight a potential shared pathophysiological mechanism and underscore the need for further studies to validate this association and elucidate the underlying connection.