Ryanodine receptor antibodies are associated with severe myasthenia gravis

Sera from 32 thymoma patients, 29 of them with myasthenia gravis (MG), were tested for the presence of circulating antibodies to the ryanodine receptor (RyR) in Western blot RyR is a channel protein essential for the excitation‐contraction coupling in skeletal muscle. MG severity was scored according to the Osserman classification during 1–17 years of follow‐up (mean 7 years). Fifteen patients (14 MG and 1 non‐MG) were RyR‐antibody positive. RyR‐positive patients had a significantly higher frequency of invasive thymomas ( p = 0.01), and also a more severe MG than RyR‐antibody negative patients ( p = 0.04). The use of immunosuppressive drugs at latest follow‐up was more frequent in RyR‐antibody positive than in RyR‐antibody negative patients ( p = 0.02). Thus the presence of RyR‐antibodies in thymoma patients is associated with a more severe disease and can be used as a prognostic marker.