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Carbon monoxide poisoning — USMLE Step 2 CK MCQ

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ModerateEmergency MedicineCarbon monoxide poisoningUSMLE Step 2 CK

A 79-year-old woman is brought to the emergency department in January because of progressive lethargy. Temperature is 32.8°C (91.0°F), blood pressure is 82/48 mm Hg, and pulse is 44/min. She is obtunded, has dry coarse skin, and has delayed deep-tendon reflex relaxation. Serum sodium is 124 mEq/L, TSH is markedly elevated, and free thyroxine is very low. Blood cultures are obtained and supportive care is begun. Which endocrine treatment should be started immediately?

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Correct answer: C — Give intravenous hydrocortisone followed by intravenous levothyroxine

Hypothermia, bradycardia, hypotension, hyponatremia, depressed mental status, and severe biochemical hypothyroidism indicate myxedema coma. Treatment must begin immediately in an intensive-care setting with intravenous levothyroxine because gastrointestinal absorption is unreliable. Stress-dose intravenous hydrocortisone should be given before or with thyroid hormone until coexisting adrenal insufficiency has been excluded; thyroid replacement can increase cortisol clearance and precipitate adrenal crisis. Oral treatment is too slow and unreliable for this emergency. Liothyronine may be added cautiously in selected severe cases, but it is not preferred as unprotected monotherapy because high serum triiodothyronine concentrations can increase cardiac risk. Glucocorticoids alone do not correct the life-threatening thyroid-hormone deficiency, and treatment should not await dynamic adrenal testing. Methimazole and propranolol treat thyrotoxicosis, the opposite disorder. Supportive warming, ventilatory and hemodynamic support, electrolyte management, and treatment of the precipitating illness are also essential.

Reference: Jonklaas J, et al. American Thyroid Association Guidelines for the Treatment of Hypothyroidism. Thyroid. 2014. https://doi.org/10.1089/thy.2014.0028