Factors influencing the clinical type and course of myasthenia gravis.

Myasthenia gravis is considered to be an autoimmune disease in which several factors reciprocally influence the clinical type and course. We investigated the relative importance of the following factors: anti-acetylcholine receptor antibody (AChR Ab), HLA, age at onset, autoimmunity, thymic abnormality, duration of treatment, change in AChR Ab titer and immunosuppressive therapy. The pretreatment-AChR Ab titer and HLA were shown to significantly influence the clinical type. On the other hand, the age at onset significantly influenced the clinical course. The finding that with an onset at less than 5-year-old there was a tendency for a good prognosis suggests an association between the immaturity of the muscle and immune systems, and the clinical course.