A 68-year-old woman with recent history of papillary thyroid cancer (Figure 1) underwent bilateral neck dissection and total thyroidectomy 3 months previously. Due to concern for residual cancer, she received radioactive iodine ablation (RAIA) therapy 1 week prior. Prior to RAIA, she was weaned off levothyroxine for several weeks. She had been observing a “low iodine” diet since the ablation. One week after RAIA, she presented to the emergency room with dizziness, weakness and fatigue. She appeared very sleepy and sluggish in her speech. There was mild non-pitting edema in the lower extremities. Vitals were within normal range.

Laboratory test showed serum Na 101 mmol/L, serum osmolality 216 mmol/kg, serum creatinine 1.3 mg/dL (baseline 1.0 mg/dL), urine osmolality 552 mmol/kg, urine Na <10 mmol/L, urine K 32 mmol/L. Additional laboratory results included TSH 39 mIU/mL,  free T4 0.32 ng/dL, total T3 <10 ng/dL. Prior to ablation, TSH was 104.5 mIU/mL (reference range: TSH: 0.45-4.12 mIU/mL, free T4 0.6-1.12 ng/dL, total T3: 80-210 ng/dL).

In the emergency department, she received normal saline bolus 500 mL with improvement of serum Na to 105 mmol/L. She was also empirically started on stress dose hydrocortisone and levothyroxine IV as well as liothyronine. Meanwhile, normal saline IV was continued for the next 12 hours. Serum Na remained at 103-108 mmol/L with no further improvement. The patient remained lethargic and was intubated for hypercapnic respiratory failure. A chest radiograph after intubation showed moderate bilateral pulmonary edema. Nephrology was consulted.

Figure 1. CT of the neck showed bilateral bulky neck masses compatible with pathologic lymphadenopathy (arrows).
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