Part of “CHAPTER 39 – THE THYROID NODULE“

Thyroid hormone has been used for many years to reduce the size of thyroid lesions thought to be dependent on TSH stimulation. In using hormone administration as a diagnostic test for thyroid nodules, the assumption is that benign lesions will show preferential reduction in size. Typically, patients are given a 3- to 6-month trial of T₄ at a dose titrated to result in undetectable serum TSH in an ultrasensitive assay or unresponsiveness of TSH to TRH stimulation, but without induction of clinical hyperthyroidism. Continued growth of a nodule or lack of reduction in size during therapy increases the suspicion of malignancy. However, an absolute reduction in size sufficient to denote benignancy has not been determined, and various investigators have adopted different criteria for response, which renders the interpretation of results more difficult. A partial response to treatment is not particularly reassuring because of the possibility of inconsistency in palpated size and/or a misleading apparent reduction in size of a nodule due to regression of surrounding normal tissue. Seven percent to 16% of nonresponding lesions harbor carcinoma, and an occasional carcinoma has exhibited partial regression.2 Largely uncontrolled studies have suggested that a complete response to suppressive therapy occurs in <10% of cases, whereas a 50% reduction in size is seen in ˜30% of cases.7 However, one double-blind controlled study found no significant difference in sonographically measured colloid nodule size reduction between a group of patients treated with suppressive doses of T₄ and those treated with placebo.54 Although 21% of thyroid hormone–treated nodules decreased >30% in volume over 6 months, equivalent size reductions were noted in nodules in the placebotreated group. Some confirmation of these findings was provided by the failure to observe significant shrinkage of nodules on T₄ therapy in two other studies.55,56 On the other hand, other workers continue to suggest that suppressive therapy may shrink both nontoxic goiter57 and thyroid nodules.58,59,60 and 61