[Correlation Between Clinical Manifestation, Prognosis and Antibody in Anti-Muscle-specific Tyrosine Kinase Antibody Positive Myasthenia Gravis].

Objective: To determine the correlation between the titer of anti-muscle-specific tyrosine kinase (anti-MuSK) antibodies (Abs) and the severity and prognosis of Musk-associated myasthenia gravis (Musk-MG). Methods: A total of 33 MuSK-MG patients diagnosed at Department of Neurology, Peking Union Medical College Hospital from May 2018 to June 2020 were prospectively included. Patients were divided into different groups according to immune state, and the immune naive patients were further divided by the Myasthenia Gravis Foundation of America (MGFA) classification. There were 28 Musk-MG patients who completed the follow-up and subdivided into different groups according to post-intervention status (PIS). Twenty-five patients who received immunotherapy were divided into corticosteroid monotherapy group (n=17) and corticosteroid combined with immunosuppressant group (n=8). The comparison of Ab titers between different MGFA groups and PIS groups was determined by Kruskal-Wallis method, and the comparison of Ab titers between different time points was analyzed by Mann-Whitney U method. Results: There were 11 males and 22 females included in the study, with an onset age of 48 (18, 73) years, of which 16 cases were immune naive and 17 cases were treated with corticosteroids or immunosuppressant at least once. In immune naive population, a significant difference of Ab titers among different MGFA phenotypes was detected (P=0.04). Ab titers were reduced by immunosuppression therapy (the median value decreased from 1.20 to 0.87, P=0.01). Twenty-four (85.7%) MuSK-MG patients achieved a good prognosis (PIS-PR/MM), 1 (3.6%) case achieved improvement (PIS-I), and 3 (10.7%) patients' condition worsened (PIS-W), there was no significant difference of Ab titers among the three groups (P=0.21). Meanwhile, there was no significant difference of Ab titers between different treatment groups (P=0.95). Conclusions: In the immune naive state, the concentration of MuSK-Ab is consistent with the severity of the disease, and the Ab titers decrease after immunotherapy. Change of Ab titers is related to the daily dosage of corticosteroid and is not consistent with PIS grades.