A 48-year-old woman with a history of Grave’s disease undergoes an urgent appendectomy. Fours hours after surgery she is found to have altered mental status and diaphoresis. Her vital signs are:
On physical examination there is no evidence of rigidity. ABG shows:
TSH is <0.01 µg U/mL. Two liters of normal saline and intravenous propranolol are administered.
Which of the following medications is NOT indicated for immediate treatment in this patient?A. Iodine
Correct Answer: A
This patient has thyrotoxicosis (thyroid storm), an acute, life-threatening hypermetabolic state of excessive thyroid hormone. Management is supportive and aimed at blocking further hormone synthesis, release, and peripheral conversion. This thyroid hormone blockade has been referred to as the four ‘Bs’: Beta-blockade; Block synthesis (ie antithyroid drugs); Block release (ie iodine); Block conversion of T4 into T3 (propranolol, corticosteroids).
Thyroid hormone synthesis can be inhibited by either the drugs propylthiouracil (PTU) or methimazole, which prevent the enzyme thyroid peroxidase from iodination of tyrosine residues on thyroglobulin. PTU also inhibits the peripheral conversion of T4 to T3. Even if synthesis is blocked, the thyroid gland still contains stores of thyroid hormone and will continue to release it for days to weeks. To suppress thyroid hormone release, large doses of iodine can be administered. Either potassium iodine or sodium iodine can be used. However, if iodine is administered before blocking thyroid hormone synthesis with an antithyroid agent, it will merely be incorporated into further thyroid hormone production. Therefore, iodine should not be administered for at least 1 hour after PTU or methimazole. Corticosteroids (hydrocortisone) inhibit peripheral conversion of T4 into T3. Moreover, many patients in thyroid storm also have suppression of the HPA axis and are adrenally insufficient.