Thyrotoxicosis caused by functioning metastatic thyroid carcinoma. A rare and elusive cause of hyperthyroidism with low radioactive iodine uptake.
A patient with progressively worsening thyrotoxicosis, refractory to medical therapy, is described. Repeated measurements of thyroidal RAI uptake over a 13 month period were low consistently and could not be explained by iodine ingestion, thyroiditis, or administration of exogenous thyroid hormone. An I-131 scan ultimately revealed striking activity at the base of the skull, reflecting ectopic excessive production of thyroid hormone by a solitary functioning metastatic thyroid carcinoma. The thyrotoxic state resolved after large doses of therapeutic I-131. Typical features of this rare cause of hyperthyroidism are discussed.
D000236:Adenoma / Q000150:complications; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism*; D008875:Middle Aged; D012888:Skull Neoplasms / Q000378:metabolism / Q000556:secondary*; D013961:Thyroid Gland / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000150:complications*; D013971:Thyrotoxicosis / Q000097:blood / Q000209:etiology*; D013974:Thyroxine / Q000097:blood
D007457:Iodine Radioisotopes; D013974:Thyroxine