Myasthenia Gravis and Thyroid Function

THE history of a recent patient with myasthenia and hyperthyroidism shows treatment of two kinds by another physician occurring during the year before she consulted us. First, radioactive iodine was used, with an athyreotic state resulting; then, replacement hormonal therapy. Neither treatment relieved the muscular weakness; in fact, it became progressively more pronounced despite increasing doses of thyroglobulin. The literature notes coincident occurrence of both maladies. In a Mayo Clinic report, hyperthyroidism occurred in 3% to 6% of all myasthenic patients1,2; on the other hand, less than 1% of hyperthyroid patients had myasthenia gravis.3Among those with two disorders, hyperthyroidism appeared first in 54%; myasthenia first in 37%; both simultaneously in 9%.2 Concerning the effect of thyroid function upon myasthenia, findings are conflicting. Some report that, as the hyperthyroidism was treated, there was a worsening of the myasthenia4-7; others reported that it improved.1-3,8,9But