Clinical features of myasthenia gravis patients with autoimmune thyroid disease in Taiwan

Objectives The aim of this study was to analyze the prevalence and clinical features of myasthenia gravis (MG) patients with and without autoimmune thyroid disease (ATD). Materials and methods Between 1999 and 2009, we reviewed a total of 1482 patients with MG. On the basis of thyroid evaluations, as well as neurological, clinical, and serological findings, the patients were divided into group A (MG patients with ATD) or group B (MG patients without ATD). The patients were categorized as having ocular myasthenia when symptoms restricted to the ocular system were present for 2years or more. Results Of the 1482 MG patients, 121 (8.2%) patients were classified into group A. Graves' disease was more predominant (5.7%) than Hashimoto's thyroiditis (1.1%) and antibody-positive thyroid disease (1.4%). MG patients with ATD were predominantly female, were younger at the onset of MG symptoms, had a higher frequency of mild MG (ocular and mild generalized MG) and thymic hyperplasia, and had lower levels of seropositive anti-acetylcholine receptor antibodies. Compared to patients without thyroid eye disease, ATD patients with thyroid eye disease had a higher frequency of ocular MG. Conclusions This is the largest review of the clinical features of MG patients with and without ATD to date. We found that compared to ocular MG, mild MG is more commonly associated with ATD. Furthermore, we observed that thymic hyperplasia is more common in MG patients with ATD, while thymoma is more common in MG patients without ATD.