RESUMEN
Myasthenia gravis is an autoimmune disease characterized by impaired neuromuscular transmission due to circulating antiacetylcholine receptor autoantibodies. The relation between myasthenia gravis and thyroid disease remains unclarified. The association is thought to be uncommon and approximately 0.2% of myasthenia gravis has been reported in patients with autoimmune thyroid disease. Clinical expression of myasthenia gravis varies, ranging from a mild localized disease such as ocular myasthenia gravis (OMG) to a severe generalized disease. A higher frequency of thyroid antibodies has been observed in OMG compared to generalized myasthenia gravis, but the exact mechanisms of this increased association between OMG and thyroid autoimmunity has not been confirmed. The "see-saw" relationship between hyperthyroidism and myasthenia gravis is presented by some authors, while others reported that the optimal maintenance of euthyroid status was essential in treatment. Today many authors agree to the latter and we think that the adequate control of hyperthyroidism is more important. We have experienced six cases of hyperthyroidism combined with OMG and it was somewhat difficult to diagnose myasthenia gravis when the patient have Graves' ophthalmopathy.