title: Serial TSH determination after T3 withdrawal or thyroidectomy in the therapy of thyroid carcinoma.
abstract: Exogenous triiodothyronine (T3) was substituted for levothyroxin or desiccated thyroid in 13 athyrotic patients previously treated for papillary, follicular, or mixed papillary-follicular carcinoma of the thyroid. After 4 weeks T3 therapy was discontinued and serial determinations of plasma thyroid stimulating hormone (TSH) concentrations were made. A roughly exponential rise in TSH values, corresponding to a doubling time of 2 days, was observed until a level of 40 microIU/ml was reached, after which the curve passed through a maximum at 20 days. The mean time required for a level of 50 microIU/ml was 11 days, and this time is suggested for TSH determination before I-131 imaging of patients with thyroid cancer. Plasma TSH values in eight patients following "total" thyroidectomy showed a much slower and more variable rise, with a mean doubling time of 7.6 days. Weekly TSH levels beginning at 15 days will provide a rational basis for I-131 imaging in this group, in whom a longer period of hypothyroidism will be required before imaging and therapy. Adherence to these protocols should minimize the duration of hypothyroidism in patients undergoing I-131 treatment of thyroid carcinoma.
mesh_terms: D000230:Adenocarcinoma / Q000628:therapy*; D006801:Humans; D007037:Hypothyroidism / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000628:therapy*; D013965:Thyroidectomy; D013972:Thyrotropin / Q000097:blood*; D013997:Time Factors; D014284:Triiodothyronine / Q000627:therapeutic use*
chemical_list: D014284:Triiodothyronine; D013972:Thyrotropin