Saturday, February 25, 2012

Myxedema Coma Treatment

Myxedema Coma Treatment

The patient with myxedema coma should be admitted to the intensive care unit, and hypovolemia and electrolyte abnormalities corrected. Mechanical ventilation may be necessary. Cardiovascular status should be monitored carefully, especially after intravenous thyroid hormone replacement. Myocardial infarction must be ruled out and blood pressure stabilized. If possible, pressors and ionotropes should be avoided because of their tendency to provoke arrhythmias in the setting of intravenous thyroid replacement. Patients with hypothermia should be covered with regular blankets; the use of warming blankets should be avoided because the resulting peripheral dilatation may lead to hypotension and cardiovascular collapse.

Thyroid Hormone Replacement
Any patient with suspected myxedema coma should be treated presumptively with thyroid hormone. While there is concern regarding the precipitation of arrhythmias or myocardial infarction by administering large doses of intravenous levothyroxine, this concern must be balanced against T4's potentially life-saving and usually nondetrimental effect.

While the necessity of intravenous thyroid hormone replacement is apparent, some controversy exists regarding the use and dosages of levothyroxine (T4) and liothyronine (T3). Because of the relatively small number of patients with myxedema coma, controlled studies comparing various dosages of T4 and T3 are lacking. Because T3 is more biologically active than T4, and because the conversion of T4 to T3 is suppressed in myxedema coma, some have advocated T3 replacement. However, parental T3 is not only expensive and difficult to obtain, it may also contribute to increased mortality.

Most authorities therefore recommend use of T4 alone. An initial levothyroxine dose of 100 to 500 μg administered intravenously should be followed by 75 to 100 μg administered intravenously daily until the patient is able to take oral replacement. The lower initial dose should be administered to patients who are frail or have other comorbidities, particularly cardiovascular disease. Elderly patients typically require 100 to 170 μg of oral levothyroxine daily.

Antibiotics
Infection is often the cause of the patient's decompensation; therefore, an infectious etiology should be sought with blood and urine cultures as well as a chest radiograph. Some authorities advocate empiric therapy with broad-spectrum intravenous antibiotics.

Steroids
Because of the possibility of secondary hypothyroidism and associated hypopituitarism, hydrocortisone should be administered until adrenal insufficiency has been ruled out. Hydrocortisone should be administered intravenously at a dosage of 100 mg every eight hours. Failure to treat with hydrocortisone in the face of adrenal insufficiency may result in the precipitation of adrenal crisis. A random cortisol level should be drawn prior to therapy, and if not depressed, the hydrocortisone can be discontinued without tapering. An adrenocorticotropic hormone stimulation test can be administered if clinically warranted.

Prognosis
The prognosis for patients with myxedema coma is difficult to define because of the small number of cases reported in the literature. The severity of the condition, however, is clear. One study reported a mortality rate of about 30 percent, while another suggests the mortality rate may be as high as 60 percent. Factors associated with a poor prognosis include advanced age, bradycardia and persistent hypothermia.

Final Comment
Family physicians should be alert for myxedema coma, particularly in elderly women with mental status changes who present during the winter months. An accurate diagnosis generally follows a careful history, physical examination and laboratory evaluation. The most important elements in treatment of myxedema coma are early recognition, presumptive thyroid hormone replacement, hydrocortisone and appropriate supportive care. While myxedema coma carries a significant mortality rate even with appropriate testing and treatment, an early diagnosis of hypothyroidism may well save a patient's life.

References:
www.ncbi.nlm.nih.gov
www.aafp.org

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