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Key Points

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  • In a critically ill patient with a goiter or history of hyperthyroidism, consider and treat thyroid storm early.

  • Thyroid storm and myxedema coma are clinical diagnoses that do not depend on the absolute levels of thyroid-stimulating hormone and free thyroxine.

  • Myxedema coma should be considered in elderly hypothyroid patients who present with hypothermia and confusion.

  • For successful treatment, it is important to try to identify a trigger that pushed the patient into the extreme state of thyroid storm or myxedema coma.

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Introduction

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Thyroid hormone (TH) is synthesized within the follicular cells of the thyroid gland. Production begins with the uptake of iodine into the follicular lumen. Thyroglobulin, produced within the follicular cell, is bound to iodine and then coupled to produce the thyroid hormones, thyroxine (T4) and triiodothyrinine (T3). Release of thyroid hormone is stimulated by one of the hormones secreted by the pituitary gland, thyroid-stimulating hormone (TSH). In turn, TSH is regulated by thyroid-releasing hormone (TRH) secreted by the hypothalamus. High levels of T4 and T3 act to suppress production of TSH and TRH via a negative feedback loop. TH released from the thyroid gland is in its less active form, T4, which is converted in peripheral organs (kidney and liver) into its 10 times more active derivative, T3. The half-life of T3 is significantly shorter, approximately a day, compared with 1 week for T4. In the serum, the majority of TH is bound to thyroid-binding globulin (TBG), making it inactive. The only active forms are free T3 and T4. After TH enters cells, it binds to its nuclear receptor and regulates expression of genes involved in lipid and carbohydrates metabolism and protein synthesis. As a net result of its action, there is an increase in basal metabolic rate.

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Emergencies related to the thyroid gland can be caused by both excess and deficiency of TH. Excess of TH can cause a syndrome referred to as thyrotoxicosis and can be caused either by excessive production of TH or its exogenous administration. In its extreme state, thyrotoxicosis can lead to a life-threatening condition called thyroid storm, a state manifesting with fever, tachycardia, and altered mental status.

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Hyperthyroidism is the term used when excessive production of TH by the thyroid is the cause of thyrotoxicosis. One of the most common causes of hyperthyroidism is Graves disease (approximately 80% of cases), in which autoimmune antibodies that bind to TSH receptors on the surface of thyroid cells stimulate production and release of TH. Other significant causes of hyperthyroidism include toxic multinodular goiter, thyroiditis, pituitary adenoma, and reaction to drugs (eg, lithium, amiodarone and iodine). Hyperthyroidism is 10 times more common in women.

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Insufficiency of TH is referred to as hypothyroidism, and 95% of the time it is caused by dysfunction of the thyroid ...

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