Thallium-201 scintigraphy of the suppressed thyroid: an alternative for iodine-123 scanning after TSH stimulation

Thallium-201 scintigraphy of the thyroid gland suppressed by autonomous nodule was compared with 123I scintigraphy after TSH stimulation. In all patients, similar images were obtained by both methods. In 20 patients, the contralateral lobe was visualized on both scans and in 14 of these, the upper pole of the ipsilateral lobe was also visualized. In one patient, neither 123I scanning after TSH nor 201TI scintigraphy showed any extranodular tissue. This study suggests that 201TI scintigraphy is a reliable alternative for scanning after TSH. It is a relatively simple method, not inducing any TSH-related allergic reactions. Iodine uptake in extranodular tissue is not stimulated and therefore, 201TI scintigraphy and radioiodine therapy can be combined on one day, without increasing the risk of radiation damage to the normal thyroid tissue with a resultant post-treatment hypothyroidism.