Papillary thyroid microcarcinoma (PTMC) has a good prognosis and is usually treated with thyroidectomy alone, with postoperative radioiodine ablation therapy being reserved for patients at risk of recurrence. Nevertheless, there is currently little consensus regarding the best strategy for following low-risk patients after surgery.OBJECTIVE
To compare 131I whole-body scintigraphy (WBS), recombinant human TSH (rhTSH)-stimulated thyroglobulin levels, and neck ultrasound for the detection of persistent or recurrent PTMC.DESIGN AND INTERVENTION
This was an observational study of patients consecutively diagnosed with intrathyroidal PTMC between April 1999 and August 2005. All participants underwent near-total thyroidectomy and, where appropriate, lymph-node dissection. Patients receiving postoperative radioiodine ablation therapy were excluded, as were those with antithyroglobulin antibodies. After surgery, all patients received levothyroxine to normalize TSH levels, and a follow-up examination was performed after 6-12 months. Patients were placed on a low-iodine diet for ≥20 days before examination. On day 1, baseline serum samples were drawn. Participants then received 0.9 mg rhTSH on days 1 and 2, and 185 MBq 131I on day 3. Neck ultrasound, WBS, and measurement of thyroglobulin and TSH levels were then performed on day 5.OUTCOME MEASURES
The primary outcome measures were thyroglobulin levels, WBS, and neck ultrasound following rhTSH stimulation.RESULTS
A total of 80 patients participated in the study (69 women and 11 men, mean age 49.4 years). PTMC had been diagnosed incidentally following treatment for multinodal goiter in 69 cases, and had been diagnosed preoperatively in 11 cases. Central lymph-node dissection was performed in all 11 cases of nonincidental PTMC. Before rhTSH stimulation, basal thyroglobulin levels were ≤1 μg/l in 76 patients and >1 μg/l in 4 patients. After stimulation, the levels remained ≤1 μg/l in 45 patients (classified as thyroglobulin-negative) but were >1 μg/l in the remaining 35 patients (classified as thyroglobulin-positive). Small nodal metastases were detected by neck ultrasound in three patients, including one who was designated thyroglobulin-negative. By contrast, WBS revealed percentage 131I uptake into the thyroid bed-indicative of the persistence of normal thyroid tissue-ranging from 0.1% to 10.2% (mean 3.1±2.6%); however, no pathologic 131I uptake was detected in any of the patients. Stimulated thyroglobulin levels were found to correlate with 131I uptake by the thyroid bed. When the patients without lymph-node metastases were subdivided by 131I uptake, all 14 patients with ≤0.5% uptake were thyroglobulin-negative, whereas 33 out of 63 patients with >0.5% uptake were thyroglobulin-positive (P<0.0001). Further follow-up was available for 74 patients (mean time after primary treatment 32±13 months). Ultrasonographic or clinical signs of persistent or recurrent PTMC were not detected in any of the 32 node-negative, thyroglobulin-positive patients.CONCLUSION
Neck ultrasound was the most sensitive method for detecting lymph-node metastases at follow-up.