Myasthenia gravis: a long term follow-up study of Swedish patients with specific reference to thymic histology

Background: Myasthenia gravis ( MG) is an autoimmune disorder of neuromuscular transmission. The majority of patients show abnormal thymic histology. Setting: The study was performed at the Myasthenia Gravis Centre, Karolinska University Hospital, and at the Immunological Research Laboratory, Centre for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden. Patients and methods: Information was collected retrospectively from 1956 and prospectively from 1975 on clinical data, concomitant diseases, concentration of serum acetylcholine receptor antibodies ( AChR- abs), immunosuppressive treatment ( IS) and response to it, in 537 patients of whom 326 were thymectomised. Follow- up time was 1.5 - 50 years. Results: Age at onset of MG increased from a median age of 24 years before 1975 to a median age of 61 years after 2000. Thymoma was found in 65, hyperplasia ( HPL) in 185 and a normal thymus in 76 patients. The trans- sternal surgical approach for thymectomy was used in 255 patients ( 78%). In five patients with thymoma, MG appeared after thymectomy. Of 537 patients, 466 ( 87%) had circulating AChR- abs. IS was given to 300 ( 56%) patients, mostly those with thymoma ( 85%). In total, 441 patients ( 82%) showed an improvement. One- third of patients with HPL, a quarter of those with thymoma, one- fifth of those with a normal thymus and one- seventh of those not operated on went into remission. Conclusion: The prognosis for the majority of patients with MG is favourable, irrespective of thymic histology. The cause may be the use of immunomodulating therapy.