It has an estimated incidence of 0.22 per million per year. The clinical picture is often that of an elderly obese female, presenting in midwinter with increased lethargy, somnolence, and confusion. The presentation is one of severe hypothyroidism, with or without coma (the term myxedema coma may, therefore, be a misnomer). The history from the patient may be inadequate, but the family may report that the patient has had thyroid surgery or radioiodine treatment in the past or that the patient has previously been receiving thyroid hormone therapy. Myxedema coma is most frequently associated with discontinuation of thyroid hormone therapy. It presents less frequently as the first manifestation of hypothyroidism. It may be precipitated by an illness such as a cerebrovascular accident, myocardial infarction, or an infection such as a urinary tract infection or pneumonia. Other precipitating factors include gastrointestinal hemorrhage; acute trauma; excessive hydration; or administration of a sedative, narcotic, or potent diuretic drug.

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