The relationship between thyroid dysfunction and diseases of muscle is well-known but not explained; the effect of thyroid hormone on myasthenia gravis, polymositis, and familial periodic paralysis has yet to be clarified. The association of hypothyroidism and a presumably unrelated myopathy in the case we report affords an unusual opportunity to observe the effect of one upon the other. Treatment with thyroid extract reversed the signs of myxedema, improved muscle function, and altered the electromyographic findings.
A 39-year-old white woman was referred to Northwestern University Medical School Clinic; she complained of muscle "stiffness" which had worsened in the past five years. At age 9 her hands became "clumsy," although she could do intricate factory work (putting springs into the tumblers of locks) at age 30. Muscle stiffness seemed to worsen through each of her four pregnancies, especially toward term. Menarche was at age 16; five years prior to