Study On The Clinical Characteristics,Diagnosis And Treatment Of MuSK Antibody Positive Myasthenia Gravis

Objective:To summarize the clinical characteristics,diagnosis and treatment of MuSK antibody positive myasthenia gravis(MuSK-MG).Methods:The clinical data of 14 MuSK-MG patients admitted to our hospital from January1,2015 to December 31,2019 were analyzed,including the patient’s gender,age of onset,symptoms of onset,the process of disease development,laboratory test results,electrophysiological,pathological,thymus examination findings,complications,diagnosis,treatment and prognosis.All of the clinical data were evaluated and compared with the other two groups,which consist of 130 AChR-MG patients and 39DSN-MG patients respectively.Moreover,previous literature review was also performed.Results:1.The onset age of MuSK-MG patients was 53.2±13.6 years,which was not significant different compared with AChR-MG patients(53.9±16.7)and DSN-MG patients(45.0±15.2)(P=0.876,P = 0.080).2.There was no significant difference in the sex ratio between the MuSK-MG group(male to female 3:11)and the AChR-MG group(male to female 48:82)(P=0.379).However,such a ratio for MuSK-MG was different from DSN-MG group(P=0.010),which was predominant in male(male to female 24:15).3.Twenty six point four percent of MG patients without AChR antibody(53cases)were MuSK-MG(14 cases),which were accounted for 7.7% of the total cases(183 cases).4.Extraocular muscle weakness was the most common[ 7/14(50.0%)] initial syndrome in MuSK-MG group,which was not statistically different from the AChR-MG group [98/130(75.4%)]and the DSN-MG group [30/39(76.9%)](P>0.05).The proportion of MuSK-MG group with purely bulbar muscle weakness at onset was higher than the corresponding AChR-MG group(P=0.044).5.The incidence of tongue muscle atrophy in MuSK-MG group was 3/14(21.4%),which was higher than AChR-MG group[1/130(0.8%)] and DSN-MG group(0)(P<0.05).6.Proportions of MGFA classification in MuSK-MG group were not significant different from AChR-MG group(P>0.05).However,compared with DSN-MG group,the proportion of MGFAⅠin MuSK-MG group was lower(P=0.001),while MGFAⅤwas higher(P=0.020);The median QMGs in MuSK-MG group were more severe than those in AChR-MG group and DSN-MG group(P<0.05).7.The positive rate of neostigmine trial in MuSK-MG group [8/14(57.1%)]was lower than those in AChR-MG group [108/109(98.2%)] and DSN-MG group [33/34(97.0%)](P<0.05).The incidence of cholinergic side effects in MuSK-MG group was higher than those in AChR-MG group and DSN-MG group [7/14(50.0%)vs.2/109(1.8%)vs.0](P<0.05).8.The proportion of thymic abnormalities in the MuSK-MG group [1/14(7.1%)]was significantly lower than that in the AChR-MG group [45/87(51.7%)](P=0.002),while not different from DSN-MG group [10/29(34.5%)](P=0.121).9.There was no significant difference in the positive rate of RNS(3Hz)among the three groups(P=0.244).MuSK-MG patients had the highest RNS positive rate of7/11(63.6%)in orbicularis oculi muscle.10.The proportion of MuSK-MG combined with other AD [6/14(42.9%)] was higher than the AChR-MG group [19/130(14.6%)](P=0.023),but not significantly different from the DSN-MG group [7/39(17.9%)](P= 0.135).11.There was no significant difference in the degree of clinical improvement between the MuSK-MG group and the AChR-MG patients treated with the same therapeutic schedule for steroids combined with immunosuppressive therapy(P>0.05).Conclusions:1.MuSK-MG patients had a onset age of 53.2 years,prominent in female,account for7.7% of the total number of MG.The onset symptom of those patients were mostly extra-ocular muscle weakness,and the proportion of bulbar muscle involvement is relatively high.Most of the patients were worsen after fatigue.The process of disease progression is similar to that of AChR-MG and DSN-MG,and the clinical manifestations were more serious,more involvement to crisis,and the incidence of tongue muscle atrophy was high.A few of those patients have mild clinical manifestations,and can be restricted in ocular muscle for a long time without obvious aggravation,and even some patients have no obvious fluctuation of muscle weakness.2.The MGFA clinical classification of MuSK-MG patients were similar to AChR-MG patients,while DSN-MG patients were prominent in MGFA Ⅰclassification,which was different from MuSK-MG patients.3.Some MuSK-MG patients were intolerant to cholinesterase inhibitors.The orbicularis oculi muscle is prone to the low frequency decrement in the electrophysiological examination.Most thymus findings were normal.The detection of serum antibody is important for diagnosis.4.MuSK-MG patients were more likely to have thyroid autoantibodies abnormalities or other autoimmune diseases,but did not affect the prognosis.5.The combination of steroids and tacrolimus can effectively treat MuSK-MG.