[Thyroid myopathy. Effect of treatment with thyroid hormones].

We studied 20 patients afflicted with primary hypothyroidism and treated with thyroid hormone replacements, with the aim of evaluating the clinical, biochemical, EMG and anatomo-pathological effects. Cramps, as well as subjective and objective proximal muscular weakness, disappeared. Seric CPK was normalized in all cases after 1-8 weeks of treatment. EMG myopathic patterns faded away in all cases. Anatomopathological changes took longer to observe; 5 cases with new biopsy showed an isolate atrophy of type II fibers, one of them after 18 months in treatment; type I fibers had mitochondrial accumula without change compared to the initial biopsy. There was a clear tendency for the destroyed fibers to become normalized and for the structures similar to the "core" to vanish.