Longitudinal dynamics and clinical significance of acetylcholine receptor blocking antibodies in myasthenia gravis.

OBJECTIVES: To investigate the longitudinal clinical relevance of acetylcholine receptor (AChR) blocking antibodies in myasthenia gravis (MG). METHODS: We prospectively studied 47 AChR-positive MG patients with 121 serial antibody measurements over a mean follow-up of 2.8 years. AChR-binding antibodies were measured by a conventional radioimmunoprecipitation assay, whereas AChR-blocking activity was measured using a competitive radioimmunoassay. Disease severity was assessed using Myasthenia Gravis Foundation of America (MGFA) classification. Longitudinal associations were analyzed using generalized estimating equations (GEE). RESULTS: Blocking antibodies (> 20% inhibition) were associated with MGFA severity across repeated observations in longitudinal GEE analysis (β = 0.045, p < 0.001), whereas binding antibodies were not significant. Among 13 patients with ocular-onset MG, all 8 who progressed to generalized disease were blocking antibody-positive, while none of the 5 patients who remained ocular tested positive. Blocking antibodies were detected in 90.5% of generalized MG patients, whereas all persistently ocular patients were negative. CONCLUSIONS: AChR blocking antibodies are associated with MG disease severity over time and may help identify ocular MG patients at risk of generalization, supporting their potential clinical relevance in MG.