Thyroid suppression and stimulation testing: The place of scanning in the evaluation of nodular thyroid disease

In the past, T3 suppression testing was often required to confirm the presence of autonomous thyroid function in patients with borderline clinical and laboratory findings suggestive of hyperthyroidism or in euthyroid patients with the stigmata of Graves' disease. Similarly, TSH stimulation testing was used to document the presence of "low thyroid reserve" in patients with borderline clinical and laboratory findings suggestive of hypothyroidism. The current availability of radioimmunoassays for triiodothyronine (T3) and thyrotorpin (TSH) plus the ability to evalate pituitary responsiveness by performing a TRH stimulation test permits a definitive diagnosis to be made in the majority of borderline situations without recourse to the more cumbersome suppression and stimulation tests. Suppression and stimulation thyroid scanning retain a unique position in the evaluation of localized areas in increased uptake of radionuclide (hot nodules), especially in patients who are euthyroid. Proof that such nodules are autonomously functioning thyroid adenomas (AFTN) greatly decreases the possibility that they represent malignant thyroid tumors. Suppression and stimulation scanning have a more limited role in the evaluation of patients with hyperthyroidism arising in a multinodular goiter, where TSH stimulation scanning may help to differentiate between toxic multinodular goiter and Graves' disease arising in a preexisting goiter.