Endocrine Abstracts

Ever since the approval of recombinant human TSH (rhTSH) prior to remnant ablation and whole body scans, usage of levothyroxine withdrawal for TSH elevation is decreasing. However the readily unavailability of rhTSH in some countries and the cost are its disadvantages. Withdrawal of levothyroxine, however, exposes the subjects to hypothyroidism.

A 26-year-old male patient admitted to our hospital for a routine checkup with no symptoms. His TSH level was 7.54 mIU/l (0.35–4.2) thus a thyroid ultrasonography was performed. A 12×10×20 mm thyroid nodule was visualized in the left lobe and the thyroid parenchyma was compatible with Hashimoto’s thyroiditis. We performed a fine-needle aspiration biopsy from the nodule which was reported suspicious for papillary thyroid cancer. The same week he underwent total thyroidectomy confirming the diagnosis of classical type papillary thyroid cancer. The tumor was 17 mm in diameter with no extra capsular or extra thyroidal invasion. We planned 100 mCI of radioactive iodine (RAI) for remnant ablation 8 weeks after the surgery. We withdrew levothyroxine 4 weeks before the planned RAI and initiated T₃ replacement which was also withdrawn 2 weeks before the scheduled RAI treatment. Two days before the scheduled RAI, the patient complained of fatigue and nausea. His serum creatinine level was 2.1 mg/dl (0.6–1.1), K 4.2 mEq/l, and creatinine kinase level was 1300 μg/l (10–120). At this point his TSH level was 50 mIU/l (0.45–4.2) and free thyroxine level was 0.5 ng/l (0.9–1.48). He was hydrated orally and parentally. Levothyroxine was initiated after the RAI and the creatinine level decreased gradually to normal limits.

Symptomatic hypothyroidism is frequently observed during levothyroxine withdrawal prior to remnant ablation with RAI. Many case reports have been presented relating hypothyroidism to rhabdomyolysis. The presented cases were generally newly diagnosed subjects with probably long-standing hypothyroxinemia. Although rare, severe hypothyroxinemia caused by temporary withdrawal levothyroxine for RAI can precipitate rhabdomyolysis and acute renal damage. Since severe side effects can occur during levothyroxine withdrawal besides symptoms of hypothyroidism, rhTSH may be preferred for TSH elevation when available.