Iodine -131 scintiscan and serum thyroglobulin levels: Both are least dependable in detection of lymphnode metastasis

Full text: Both Iodine-131 scan and estimation of serum thyroglobulin (Tg) levels are used for follow-up of patients with differentiated thyroid carcinoma (DTC). Thyroglobulin level is presently getting more acceptance among the thyroidologist for detection of metastatic disease. This retrospective analysis was carried out in 184 patients to evaluate the efficacy of serum Tg and Iodine-131 scan in follow up of DTC. All the patients had near total or sub-total thyroidectomy. The post-therapy WBS was performed in all patients. We measured serum Tg level 5-7 months after thyroidectomy (on thyroxin) followed by Iodine-131 whole body scans after stopping thyroxine. Then yearly Tg and whole body scans were performed. Metastatic nodules in the neck were detected by palpation, ultrasonogram, scan and confirmed by biopsy. In post therapy scan it was found that 7 cases had distant metastases having average Tg levels of 76.98 ngm. We found 128 (69.56%) scan negative and 56 (30.34%) scan positive cases after first therapeutic dose. Before the scan, Tg level was 4.71 ± 2.92 ngm in patients with negative scan and 10.94 ± 4.78 ngm in scan positive cases. During follow up scan Tg levels was 2.3 ± 1.4 ngm in earlier scan negative cases and 13.02 ± 2.32 ngm in scan positive cases. 12 patients showing recurrence on follow up scans had Tg levels of 23.43±5.9 ngm. 16 patients with metastasis showed Tg levels to be 81.38±15.8 ngm. In 8 neck lymph node positive patients, Tg level was 8.2 ± 2. 4 ngm. 9 patients having negative scan but biopsy positive palpable lymph node had Tg level of 5.7±1.6 ngm. The strategy in follow-up of such patients should rely on the results of the 131-I whole body scan (WBS) obtained after the therapeutic administration of the ablative dose of 131-I as the post therapy scans are more sensitive than the diagnostic scan. In this study we had detected 7 cases of distance metastasis in post-therapy WBS. The interesting finding in this study is that patients with lymph node metastasis had little rise of Tg level. It is concluded that both, I-131 whole body scintiscan and estimation of serum Tg level have excellent efficacy for detection of recurrence and distance metastasis but p oor sensitivity for detection of lymph node metastasis. So meticulous palpation and ultrasonography of regional node of neck is very important for detection of lymph node metastasis. (author)