What is the role of thyroid hormone therapy in the treatment of myxedema coma (crisis)?

Updated: Aug 31, 2020
  • Author: Mohsen S Eledrisi, MD, FACP, FACE; Chief Editor: George T Griffing, MD  more...
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The ideal mode of therapy and doses of thyroid hormone therapy in myxedema coma remain controversial due to the rarity of the condition and lack of clinical trials. Some clinicians favor the administration of levothyroxine (T4), while others prefer a combination of T4 and liothyronine (T3). [3, 4, 30, 31] The American Thyroid Association recommends combination therapy with T4 and T3. [32]

Because of reduced gastrointestinal absorption, intravenous thyroid hormone therapy is advised.

An intravenous loading dose of 300-600 micrograms of levothyroxine (T4) is followed by a daily intravenous dose of 50-100 micrograms. [4] Larger doses of T4 probably have no advantage and may be dangerous. [33]  The lower end of the dosing range is recommended in older patients, those at risk for cardiac complications such as myocardial infarction and arrhythmias, and in patients with coronary artery disease, since full-dose T4 therapy may worsen myocardial ischemia by increasing myocardial oxygen consumption. [32]

Because the rate of conversion of T4 to the active hormone T3 can be reduced in these patients, the addition of T3 along with T4 has been recommended. [32] T3 has a quicker onset of action than T4, as increases in body temperature and oxygen consumption has been reported to be faster with T3 therapy compared to T4. [4] T3 therapy is given as bolus of 5-20 micrograms intravenously and to be continued at a dosage of 2.5-10 micrograms every 8 hours depending on the patient's age and coexistent cardiac risk factors. [32]

Intravenous levothyroxine treatment in severely hypothyroid patients usually leads to improvement in cardiovascular, renal, pulmonary, and metabolic parameters within a week. Serum T4 and T3 concentrations may improve or normalize with a similar time frame, with more gradual improvement in serum TSH. Thus, the therapeutic endpoints in myxedema coma should be improved mental status, improved cardiac function, and improved pulmonary function.

Measurement of thyroid hormones every 1-2 days is suggested. [32] Failure of TSH to decrease or of thyroid hormone levels to increase suggests the need to increase doses of T4 and/or add T3.

The treatment is changed to the oral form once the patient is able to take medications by mouth.

A literature review by Borzì et al reported that while myxedema coma may develop in elderly people in whom hypothyroidism is untreated or undertreated, frailty, polypharmacy, and a high risk for the development of overtreatment symptoms must be accounted for when replacement therapy is administered to older patients. The investigators also stated that hypothyroidism occurs more frequently in the elderly, with the aging process affecting the hypothalamic-pituitary-thyroid axis and its hormones. [34]

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