Clinical usefulness of anti-muscarinic type 3 receptor autoantibodies in patients with primary Sjögren's syndrome

ObjectiveTo elucidate the clinical values of anti-M3R in Sjogren's syndrome (SS) in the largest cohort for an anti-M3R study.MethodsThe plasma of 361 subjects (156 primary SS [pSS], 62 non-SS-sicca [SICCA] 40 systemic lupus erythematosus [SLE], 50 rheumatoid arthritis [RA], and 53 healthy controls [HC]) was screened using our modified On-Cell-Western assay. Saliva from pSS (n=37) compared to SICCA (n=26) was also analysed. The sensitivity and specificity of anti-M3R and its association with comprehensive clinical and laboratory features were determined.ResultsPlasma-anti-M3R was higher in pSS compared to other groups, differentiating pSS with good-to-excellent diagnostic power with a specificity of 85% and a sensitivity between 75% and 98%. pSS plasma-anti-M3R was positively correlated with ocular staining scores, anti-Ro/SSA, IgG, beta 2-microglobulin, ESR, and ESSDAI. It was negatively correlated with WBC, C4, and salivary scintigraphic indices. Saliva-anti-M3R was 359 times higher in pSS than in SICCA. Interestingly, the agreement between the 2002 American European Consensus Group criteria and the criteria substituted with plasma-anti-M3R for the lip biopsy reached 92%, with a significant kappa of 0.824.ConclusionAnti-M3R enhances sensitivity and specificity for SS diagnosis, correlating with ocular dryness and glandular hypofunction, and the haematological/biological domains of the ESSDAI. Our findings also highlight the clinical significance of anti-M3R in SS diagnosis, especially where clinical assessments, such as lip biopsy, sialometry, or ocular evaluation, by multi-disciplinary specialists are limited.