Thyroid storm is a rare but severe and life-threatening complication of hyperthyroidism. It occurs when overactive thyroid activity leads to hypermetabolism, the end result being death from cardiac arrest or multiple organ failure.
It is characterized by a high fever (temperatures often above ), fast and often irregular heart beat, elevated blood pressure, vomiting, diarrhea, and agitation. Hypertension with a wide pulse pressure occurs in early to mid crisis, with hypotension accompanying shock occurring in the late stage. Heart failure and heart attack may occur. Death may occur despite treatment. Most episodes occur either in those with known hyperthyroidism whose treatment has been stopped or become ineffective, or in those with untreated mild hyperthyroidism who have developed an intercurrent illness (such as an infection).
The primary treatment of thyroid storm is with inorganic iodine and antithyroid drugs (propylthiouracil or methimazole) to reduce synthesis and release of thyroid hormone. Temperature control and intravenous fluids are also mainstays of management. Beta blockers are often used to reduce the effects of thyroid hormone. Patients often require admission to the intensive care unit.
A life-threatening medical emergency, thyroid storm has a mortality rate of up to 25% despite treatment. Without treatment, the condition is very likely fatal, with a mortality rate of 80-100%. Historically, the condition was considered untreatable, with hospital mortality rates approaching 100%.
Signs and symptoms
Thyroid storm is characterized by an acute onset of symptoms of hyperthyroidism (fast heart rate, restlessness, agitation) accompanied by other features such as fever (temperatures often above 40 °C/104 °F), hypertension, mental status changes, diarrhea, and vomiting.
Individuals can exhibit varying signs of organ dysfunction. Patients may experience liver dysfunction, and jaundice (yellowing of the skin), which is considered a poor prognostic sign. Cardiac (heart) symptoms include abnormal heart rhythms, myocardial infarction (heart attack), and congestive heart failure, which may lead to cardiovascular collapse. Mortality can be as high as 20–30%.
In some situations, individuals may not experience the classic signs of restlessness and agitation, but instead present with apathetic signs of weakness and confusion.
Causes
The transition from hyperthyroidism to thyroid storm is typically triggered by a non-thyroidal insult including, but not limited to fever, sepsis, dehydration, myocardial infarction, and psychiatric diseases. Individuals are at higher risk of thyroid storm if their hyperthyroidism is incompletely treated or if their anti-thyroid drugs are discontinued. Many of these individuals have underlying primary causes of hyperthyroidism (Graves' disease, toxic multi-nodular goiter, solitary toxic adenoma, or amiodarone). However, thyroid storm can occur in individuals with unrecognized thyrotoxicosis experiencing non-thyroid surgery, labor, infection, or exposure to certain medications and radiocontrast dyes.
Pathophysiology
The precise mechanism for the development of thyroid storm is poorly understood. In the human body, thyroid hormone may be free (biologically active T3/T4) or bound to thyroid binding hormone (biologically inactive) to be transported. The release of thyroid hormone is tightly regulated by a feedback system involving the hypothalamus, pituitary gland, and thyroid gland. Hyperthyroidism results from a dysregulation of this system that eventually leads to increases in levels of free T3/T4. The transition from simple hyperthyroidism to the medical emergency of thyroid storm may be triggered by conditions (see Causes) that lead to the following:
Increases in free thyroid hormone
Individuals with thyroid storm tend to have increased levels of free thyroid hormone, although total thyroid hormone levels may not be much higher than in uncomplicated hyperthyroidism. The rise in the availability of free thyroid hormone may be the result of manipulating the thyroid gland. In the setting of an individual receiving radioactive iodine therapy, free thyroid hormone levels may acutely increase due to the release of hormone from ablated thyroid tissue.
Decrease in thyroid hormone binding protein
A decrease in thyroid hormone binding protein in the setting of various stressors or medications may also cause a rise in free thyroid hormone.