Patients and Controls
Between July 2019 and April 2021, 90 patients with MG were enrolled from the Department of Neurology of the First Affiliated Hospital of Soochow University. All patients were diagnosed with MG according to typical clinical features, neostigmine tests, repetitive nerve electrical stimulation, fatigue tests and positive acetylcholine receptor antibody (AChR-Ab) results. Simultaneously, 36 healthy controls (HCs) matched to patients with MG for sex, age, and race were enrolled from the hospital’s physical examination center. The study subjects were excluded if they had one of the following conditions: other autoimmune diseases, acute infectious diseases, malignant tumor (except thymoma), mental illness, or pregnancy or lactation. The quantitative MG score (QMG) was used to assess the disease severity, and all patients received standard treatment after admission to the hospital. The clinical characteristics of the study subjects are shown in Table 1.
Patients with MG were classified into different subgroups based on sex, age at onset, Myasthenia Gravis Foundation of America (MGFA) classification, thymic histology, and AchR-Ab results. According to the MGFA classification[16], patients were classified as having ocular MG (OMG) or generalized MG (GMG). All patients underwent enhanced chest computed tomography (CT) examinations and were divided into an abnormal thymus group (with thymoma or thymic hyperplasia) and a normal thymus group (without thymoma or thymic hyperplasia). Due to the low positive proportion of anti-MuSK antibodies in the Chinese population[17], the concentrations of AchR-Ab (positive cut-off value was 0.45 nmol/L) were detected in all patients with MG, and patients were divided into the AchR-Ab-positive group and the AchR-Ab-negative group (cut-off value of 0.45 nmol/L).
Thirty-nine patients with untreated stage MG (USMG), 22 patients with recurrence stage MG (RSMG), and 42 patients with paracmasis stage MG (PSMG) were recruited from the Department of Neurology of the First Affiliated Hospital of Soochow University between July 2019 and June 2021. USMG was defined as the first onset without treatment, including glucocorticoids, immunosuppressants, plasma-exchange therapy or intravenous immunoglobulins in the past 3 months. RSMG was defined as the exacerbation of the original symptoms or signs or the recurrence of symptoms after improvement. The duration of recurrence exacerbations should be longer than 24 h, and the QMGs should be increased. PSMG was defined as the absence of symptoms or signs of MG, with or without weakness of eyelid closure, and no weakness of any other muscle upon careful examination[18]. The demographic and clinical characteristics of all study populations are summarized in