Provided herein is a method of diagnosing muscle specific tyrosine kinase specific autoimmune myasthenia gravis in an individual. Generally, in the method a level of muscle specific tyrosine kinase binding to B cells is determined in a sample from an individual. A significant increase in the level of muscle specific tyrosine kinase reactive B-cells compared to that in a healthy individual indicates the presence of muscle specific tyrosine kinase autoimmune myasthenia gravis. Also provided is a fluorophore-muscle specific tyrosine kinase conjugate and a kit comprising the same useful to test the frequency of muscle specific tyrosine kinase binding B cells expressing specific markers, for diagnosis or as biomarker for muscle specific tyrosine kinase autoimmune myasthenia gravis.
