Endocrine Abstracts

Background

Resistance to thyroid hormone (RTH) involves an altered tissue response to thyroid hormones. RTH is characterized by increased serum thyroid hormone (TH) levels with nonsuppressed serum thyroid-stimulating hormone (TSH) levels. Herein, we report a rare case of RTH with recurrent papillary thyroid carcinoma (PTC).

Patient findings

A 38-year-old female patient was admited to outpatient clinic for the evaluation of neck swelling. She had no thyrotoxic symptoms and there was no family history of thyroid cancer. Physical examination revealed a 1 cm thyroid nodule and mildly enlarged thyroid gland. The initial laboratory examination revealed a normal level of TSH [(3.28 uIU/ml (0.35–5.5)] despite elevated levels of TH [(free T4: 2.11 ng/ml (0.74–1.52), free T3: 6.25 pg/ml (2.3–4.2)]. Thyroid autoantibodies were not detected against thyroglobulin, thyroperoxidase and TSH receptor. Normal pituitary gland was found in the MRI performed to exclude TSHoma. Thyroid ultrasonography (USG) showed multiple hypoechogenic nodules, the largest of which was 13x9x7 mm in diameter, in both lobes. Fine-needle aspiration was performed for the largest nodule with suspicious features of malignancy in the left lobe and the cytologic diagnosis was ’susupicious of malignancy’ (Bethesda Category 5). She underwent total thyroidectomy with central lymph node dissection (LND). The histopathological results revealed classic PTC (tumor-node-metastasis staging; T1bN1bM0) in the left thyroid lobe with metastatic central lymph nodes. Tumor size was 1.3×0.7 cm. For to ensure the TSH suppression after surgery, levothyroxine therapy was initiated 150 mg/day. After six months of levothyroxine therapy her TSH level was still elevated (TSH 176.3 µIU/ml). Therefore the dose was gradually increased up to 300 mg/day. Recurrence of PTC with regional lymph node metastasis were revealed 12 months after surgery. She underwent re-surgery for complementary LND. Then she received radioiodine ablation therapy (150 mCi). In her last follow-up visit 18 months later, serum TSH level decreased to 33.2 uIU/ml. Serum free T4 and T3 levels were normal and thyroglobulin level was <0.20 ng/ml. She had no symptoms and signs of hypothyroidism. Also, her neck USG examination showed no pathological lymph node.

Conclusion

Only a few cases have been reported in the literature showing the coexistence of RTH and thyroid carcinoma. TSH suppression may not be obtained despite increasing doses of levothyroxine in patients with RTH and PTC, as was the case we report. Further studies are needed to reach a consensus on the management of thyroid carcinoma in patients with THR.