The study of serum muscarinic acetylcholine receptor subtype 3 (m3AChR)-Specific autoantibodies level in rheumatoid arthritis patients with secondary sjogren syndrome

Background: Dry eyes and mouth are symptoms of Sjogren syndrome, which can occur on its own and be referred to as primary Sjogren syndrome or in conjunction with other rheumatic diseases like rheumatoid arthritis and be referred to as secondary Sjogren syndrome. Anti-muscarinic type 3 receptors have been linked to neurological issues as well as secretory dysfunction in Sjogren patients. Consequently, the purpose of this study is to determine the serum level of muscarinic acetylcholine receptor subtype 3 (m3AChR)-specific autoantibodies in rheumatoid arthritis (RA) patients and evaluate its relationship to disease activity, functional disability, and to study its role in the development of secondary Sjogren syndrome manifestations in those patients.

Methods: In this cross-sectional study, 30 RA patients with secondary Sjogren syndrome signs and 30 RA patients without secondary Sjogren syndrome manifestations were included, along with 30 healthy volunteers who were aged, and sex matched as controls. All participants underwent thorough clinical examination, evaluation of disease activity using the DAS28 score, assessment of functional status using the modified health assessment questionnaire (MHAQ), and evaluation of the serum level of (m3AChR) by (ELISA).

Results: When compared to RA patients without secondary Sjogren syndrome and healthy controls (20.09 ± 4.24, 18.36 ± 3.59 ng/ml respectively), the serum level of m3AChR antibodies among 30 RA patients with secondary Sjogren syndrome considerably increased (mean 25.98 ± 4.81 ng/ml).Analysis of the m3AChR's (ROC)-curve revealed that the three groups under study differed significantly (P < 0.001), with the AUC (0.806), cutoff (> 22.63ng/ml), sensitivity (73.33%), and specificity (86.67%) all exceeding the threshold. Additionally, there was a significant positive connection between the serum level of m3AChR and the following variables (P < 0.05): DAS scores, MHAQ score, number of tender & swollen joints, and acute phase reactants.

Conclusion: Autoantibodies against m3AChR may be one of the serum components involved in the pathophysiology of secondary Sjogren syndrome in RA patients, and because of their high sensitivity and specificity, they can be utilized as a diagnostic marker in these individuals.