Failure of TSH rise prior to radio-iodine therapy for thyroid cancer: implications for treatment.

We describe three patients with well-differentiated thyroid carcinoma in whom no rise in serum thyroid-stimulating hormone (TSH) was observed after the discontinuation of thyroid hormone. In one patient, TSH deficiency was due to panhypopituitarism secondary to the empty sella syndrome. This patient initially failed to respond to (131)I but was subsequently given purified porcine TSH prior to further (131)I therapy. This resulted in a significant fall in the thyroglobulin level. In two further patients, TSH levels were suppressed by functioning follicular thyroid cancer. There was an unexpectedly good (131)I uptake by metastases and they responded clinically. The failure of TSH levels to rise after thyroid hormone withdrawal should prompt investigation of the pituitary-thyroid axis. In patients with hypopituitarism, exogenous TSH is recommended, to increase the (131)I uptake. In contrast, when TSH is suppressed by functioning tumour, radio-iodine treatment may still be effective.