Evaluation of the relationship between gastrointestinal involvement features and anti muscarinic receptor 3 antibodies in patients with systemic sclerosis

Gastrointestinal system (GIS) involvement in Systemic Sclerosis (SSc) is the leading cause of morbidity. Non-invasive biomarkers are needed for GI involvement. The role of anti-muscarinic 3 receptor (anti M3R) antibodies in dysmotility has been demonstrated in GIS involvement. In this study, we aimed to evaluate the relation of GIS involvement of patients with SSc with the anti-M3 antibody. This study was conducted with 41 patients with SSc and 5 healthy controls. All patients' GIS complaints were questioned in detail. MUST, ESPEN and UCLA SCTC GIT 2.0 scores were calculated. Sandwich-ELISA assay was used to detect anti M3R antibody (MyBioSource, Inc. San Diego, USA). 31 (85,4%) of the patients were female, 32 (78,0%) had limited SSc, mean age was 53.6 ± 13.5 years, median disease duration was 15,0 years (6,00-21,0). 37 (90,2%) patients had GIS involvement. Anti M3R antibody titers (as optic density, OD) in systemic sclerosis patients were not significantly different between healthy controls (median 0,18 OD 0,13-1,65 vs. 0,25 OD 0,12-0,53; p: 0,61). Anti M3R antibody was positive in 18 (46,1%) patients. Anti M3R antibody titers were found to be lower in patients with fecal incontinence than in those without (median 0,13 OD 0,12-0,42 vs. 0.40 OD 0,13-2,75; p: 0,05). Patients with weight loss tended to have higher antibody titers than those who did not (median 0,64 OD 0,13-2,81 vs. 0,14 OD 0,12-0,26; p: 0,09). Anti M3R antibodies were negative in all patients (n=5) with positive anti-centromere antibodies, and positive in all (n=4) patients with myositis. According to the total UCLA SCTC GIT 2.0 score, no correlation was found between moderate to severe GI involvement and anti M3R antibody titers (p: >0.05 for all). Anti M3R antibody titers and the number of antibody positive patients were not different between groups of patients with and without malnutrition as determined using the MUST score and ESPEN criteria (p: >0,05 for all). As a result, in this study, anti M3R antibody positivity was detected at a significant rate in patients with SSc. No correlation was found between anti M3R antibody positivity or titers and total UCLA SCTC GIT score or risk of malnutrition. Keywords: Systemic sclerosis, GIS involvement, Anti M3R antibody