Symptomatic hyponatremia in association with a low-iodine diet and levothyroxine withdrawal prior to I131 in patients with metastatic thyroid carcinoma.
BACKGROUND
Strategies to improve I131 uptake in thyroid carcinoma include levothyroxine (LT4) withdrawal or thyrotropin (TSH) administration along with a low-iodine diet. We report five patients with papillary or follicular thyroid carcinoma who developed symptomatic hyponatremia during LT4 withdrawal and low-iodine diet.


RESULTS
Four patients had pulmonary and/or brain metastases. All had restricted iodine intakes during LT4 withdrawal. Presenting complaints included weakness, dizziness, fainting spells, lethargy, and/or nausea. Baseline serum sodium levels while on LT4 suppression were normal. During presentation all were hypothyroid and serum sodium ranged from 110 to 121 mmol/L (normal 135-148). Despite hyponatremia, the plasma renin activity and serum aldosterone levels were suppressed, indicating volume expansion. The hyponatremia responded to fluid restriction and normalized after LT4 replacement. Low sodium intake, inappropriate antidiuretic hormone secretion syndrome (SIADH)-like disorder secondary to hypothyroidism and/or lung or cerebral metastases may have contributed to hyponatremia.


CONCLUSIONS
The development of hyponatremia during LT4 withdrawal and low-iodine diet in otherwise healthy patients with thyroid carcinoma is extremely rare. However, elderly patients with metastatic thyroid carcinoma need observation during LT4 withdrawal combined with a low-iodine diet and should receive instruction to take iodine-free sodium chloride. Free water restriction may be necessary in some patients.
Shakir
Mohamed K M
MK
Endocrinology and Metabolism Department, National Naval Medical Center, Bethesda, Maryland 20889-5600, USA. mohamed.shakir@bethesda.med.navy.mil
Krook
Linda S
LS
Schraml
Frank V
FV
Hays
James H
JH
Clyde
Patrick W
PW
D000368:Aged; D000369:Aged, 80 and over; D000450:Aldosterone / Q000097:blood; D018265:Carcinoma, Papillary, Follicular / Q000188:drug therapy / Q000532:radiotherapy* / Q000556:secondary; D004032:Diet; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000139:chemically induced* / Q000175:diagnosis / Q000517:prevention & control; D007455:Iodine / Q000378:metabolism*; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics / Q000627:therapeutic use*; D008175:Lung Neoplasms / Q000556:secondary; D008297:Male; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics / Q000627:therapeutic use; D012964:Sodium / Q000097:blood; D017673:Sodium Chloride, Dietary / Q000627:therapeutic use; D013375:Substance Withdrawal Syndrome; D013964:Thyroid Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*; D013972:Thyrotropin / Q000627:therapeutic use; D013974:Thyroxine / Q000008:administration & dosage / Q000009:adverse effects*
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D017673:Sodium Chloride, Dietary; D000450:Aldosterone; D013972:Thyrotropin; D007455:Iodine; D012964:Sodium; D013974:Thyroxine