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.