Two cases of thyroid carcinoma that were not stimulated by recombinant human thyrotropin

Recombinant human TSH (rhTSH) is being widely used to monitor patients who were previously treated for differentiated thyroid cancers for evidence of recurrence. Its value lies in the avoidance of recurrent episodes of hypothyroidism in the follow-up protocols. rhTSH is also being evaluated as a potential therapeutic adjunct that would spare patients the experience of becoming hypothyroid when undergoing thyroid remnant ablation or treatment for metastases. In some centers, rhTSH is also used to support compassionate care of patients with advanced disease who cannot safely become hypothyroid. The I-131 uptake response to rhTSH, presently an off-label application, is expected to be similar to that of endogenously raised TSH levels. The two cases presented here are cautionary tales in which I-131 uptake by metastases was present under hypothyroid conditions, but absent in one patient and present in only a portion of the lesions in the other, with rhTSH stimulation.