Myasthenia gravis with muscle specific receptor tyrosine kinase antibodies

Abstract

Objectives To compare the characteristics of myasthenia gravis (MG) with different antibodies.Methods The muscle specific receptor tyrosine kinase (MuSk) and acetylcholine receptor (AChR) antibodies were detected in the sera of 119 MG patients,and fluoroimmunoprecipitation assay and cell based assay were applied. The clinical features of AChR-Ab positive,MuSK-Ab positive and serum negative MG patients were compared.Results There were 90 AChR-Ab positive sera tested out from the 119 MG sera,and 5 sera found with MuSK-Ab in the 29 AChR-Ab negative sera.There was no significant difference among the three groups regarding sex and age at onset.There were 3/5 of MuSK-Ab positive patients with predominantly bulbar paralysis,2/5 of MuSK-Ab positive patients were classified as MGFA Ⅲ to Ⅴ,and 79.2% (19/24) of serum negative patients were classified as MGFA Ⅰ.There was significantly positive relation between the levels of MuSK antibodies and disease severity (r=0.941,P=0.014).Neither thymic hyperplasia nor hymoma were found in MuSK-Ab positive patients.Conclusions MuSK antibodies are only detected out in the sera without AChR-Ab.The MuSK-Ab positive patients are mainly involved bulbar muscles,and without thymus abnormality.MuSK-MG is different with the AChR MG. Key words: Myasthenia gravis; Receptor protein-tyrosine kinases; Fluoroimmunoassay