We studied ovarian function retrospectively in 66 women who had regular menstrual cycles before undergoing complete thyroidectomy for differentiated thyroid cancer and subsequent thyroid remnant ablation with 131I. Eighteen women developed temporary amenorrhea accompanied by increased serum gonadotropin concentrations during the first year after 131I therapy. No correlation was found between the radioactive iodine dose absorbed, thyroid uptake before treatment, oral contraceptive use, or thyroid autoimmunity. Only age was a determining factor, with the older women being the most affected. We conclude that radioiodine ablation therapy is followed by transient ovarian failure, especially in older women.

We performed a prospective random study to assess possible thyroid stunning by a 185-MBq iodine-131 dose used to diagnose thyroid remnants. Patients with differentiated thyroid carcinoma were included after total or near-total thyroidectomy. They were randomly assigned to two groups. In group 0 (G0, 32 patients), iodine-123 administration only was used to diagnose thyroid remnants and/or metastasis, so that no thyroid stunning by 131I would occur. In group 1 (G1, 19 patients), diagnostic imaging was performed with 123I and 185 MBq 131I. 123I imaging was less sensitive than 131I imaging in identifying thyroid remnants in both groups (94%). Thyroid uptake of 123I was measured in both groups (at 2 h) and was not significantly different between the groups. Patients with thyroid remnants who remained in the study (28/32 in G0, 17/19 in G1) were treated with 370 MBq 131I, 5 weeks after treatment (mean time, range 12-84 days). In 12/17 G1 patients thyroid uptake measurement was repeated immediately before treatment. Uptake was equal to 1.97% +/- 0.71% and significantly lower (P < 0.05) than the previous measurement (3.76% +/- 1.50%). Patients were imaged 7 days after administration of the therapeutic dose and the images were compared with the diagnostic images. In 28/28 G0 patients thyroid remnants were unchanged and clearly seen. In 5/17 G1 patients, however the remnants were hardly identified, although they had been clearly seen at the time of diagnosis. We conclude the following: (1) a diagnostic dose of 185 MBq 131I decreases thyroid uptake for several weeks after administration and can impair immediate subsequent 131I therapy; (2) 123I is slightly less sensitive than 131I in identifying thyroid remnants; and (3) the need to scan for thyroid remnants remains to be confirmed, since only 2/51 patients enrolled in this study were not treated with 131I.

We report four patients with papillary thyroid cancer who had upper retropharyngeal node involvement demonstrated by 131I scintigraphy. Three patients presented with a thyroid nodule and enlarged jugular nodes. Total thyroidectomy was performed with node dissection. Pathology demonstrated papillary carcinoma with several metastatic nodes. 131I scanning 4 weeks after surgery demonstrated increased uptake in an upper retropharyngeal node. In one patient, thyroidectomy had been performed 21 years previously. Increased thyroglobulin level led to 131I scanning, which showed focal retropharyngeal uptake. All four patients had asymmetrical uptake at mouth level with focal uptake close to the sagittal plane. A lateral projection showed focal uptake between the base of the skull and the mandibular angle, behind the region of the mouth and nose. CT in all cases and MRI in one case confirmed the presence of an enlarged node. The mass was removed surgically in two patients and pathology confirmed the papillary nature of the metastatic node. Two patients were treated by 131I. Focal uptake of 131I in the region of the mouth is ambiguous, since salivary uptake of 131I is a common finding on scintigraphy. In cases of asymmetrical uptake in the region of the mouth, a lateral projection of the head therefore allows the correct diagnosis.

Thyroid stunning is usually defined as the inhibition or suppression of iodide trapping by remnant thyroid tissue or by functioning metastases following a diagnostic dose of 131I. The risk of stunning increases progressively with larger doses. Because the threshold above which this effect occurs in thyroid remnants seems to be between 37 MBq and 111 MBq of 131I, therapeutic 131I doses of 3.7 GBq may cause stunning. We describe stunning of papillary thyroid cancer lung and bone metastases after a therapeutic dose of 131I (3.7 GBq). A T1 bone metastasis and bilateral lung metastases were diagnosed by post-therapeutic dose whole-body scan. Nuclear MRI detected another lesion at T4, whose 131I fixation was not obvious. An additional 0.7 GBq were given after recombinant TSH, 37 days after the therapeutic dose; 24 h later, uptake by the lung and T1 metastases had disappeared, but trapping was again seen 6 months later on the post-therapeutic scan. This re-appearance is evidence in favour of the transitory and reversible character of stunning, and confirms its correspondence to the decreased ability of viable thyroid cells to trap iodine and not to their destruction. A better understanding of stunning would make it possible, in the event of rapidly progressing disease and in conjunction with recombinant thyroid stimulating hormone (TSH), to give several therapeutic doses of 131I in close succession without each dose hampering the effectiveness of the subsequent one.

The Minidose outpatient ablation protocol is effective and diagnostically useful in low-risk DTC.