Life-threatening hyponatremia following a low-iodine diet: a case report and review of all reported cases.

OBJECTIVE: To report a case of life-threatening hyponatremia as a complication of a 4-week long low-iodine diet and highlight the risk factors for this complication by reviewing all previously reported cases.

METHODS: The clinical and biochemical data from the study patient are presented and the pertinent literature is reviewed. A risk analysis for this complication is highlighted.

RESULTS: A 66-year-old Vietnamese woman had a total thyroidectomy and bilateral neck lymph node dissection for papillary thyroid carcinoma. A whole body radioiodine scan demonstrated 2 foci of activity in the anterior neck. The patient received recombinant human thyrotropin (rhTSH) and was admitted for radioiodine therapy. She had strictly adhered to a low-iodine diet for 4 weeks in preparation for ablation. The patient was on a thiazide diuretic for her hypertension, which was discontinued on admission. On admission, the patient started feeling light-headed, dizzy, and nauseated. Blood tests revealed a critical serum sodium concentration of 107 mEq/L. Further investigations confirmed hypotonic hyponatremia, which had developed despite being euthyroid after receiving rhTSH. The patient was managed accordingly and made a full recovery.

CONCLUSIONS: This case, in addition to the reviewed cases, emphasizes the importance of preventing and managing this rare but relatively dangerous complication. Based on an analysis of the reviewed cases, the risk factors for developing this complication are a prolonged low-iodine diet, the elimination of salt from the diet, and the use of thiazide diuretics. All patients in the reported cases were older than 65 years of age.