[T3, T4, TSH and circulating antithyroglobulin antibodies in myasthenia gravis]

Myasthenia gravis (MG) is a rare neuromuscular disease which is known to be associated with hyperthyroidism at high frequency (3-10%). These investigations, however, are basing on studies of the basal metabolic rate, protein bound iodine (PBI) and the thyroidal radioiodine uptake. In our study (104 MG patients, 104 control subjects) we wanted to evaluate thyroid function on the basis of T3, T4, TBG and TSH radioimmunoassays and in addition we looked for the presence of circulating antithyroglobulin antibodies (Tab) and antimicrosomal antibodies (Mab). The following thyroidal states were disclosed: Thyrotoxicosis (5.8%), hypothyroidism (1.9%), preclinical hypothyroidism (3.8%) and euthyroidism (88.5%). Twenty-eight myasthenic patients were Mab-positive and twelve in addition Tab-positive. Comparing the twenty euthyroid antibody-positive MG-patients with euthyroid antibody-negatives no statistically significant differences were found in thyroid function parameters. It is discussed that part of the thyroid antibody-positive patients may have a symptomless autoimmune thyroiditis which is finally resulting in hypothyroidism via a preclinical hypothyroid status.