Thyroid storm

Definitions & Key takeaways

Thyroid storm, also known as a thyrotoxic crisis, is a rare but life-threatening medical emergency caused by a sudden and severe worsening of hyperthyroidism (overactive thyroid). It is more common in individuals with untreated or poorly controlled hyperthyroidism and may be triggered by stress, infection, surgery, or other medical conditions.

Signs and symptoms include high fever, tachycardia, high blood pressure, agitation, confusion, sweating, vomiting, diarrhea, and in severe cases, seizures or coma. It can be fatal if left untreated, and prompt medical attention is necessary. The treatment involves medications like β-blockers, propylthiouracil, corticosteroids, and potassium iodide.

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Introduction0:00–0:22

Thyrotoxic crisis, more commonly called thyroid storm, is a severe, acute complication of hyperthyroidism. In hyperthyroidism, there’s an excess of thyroid hormone, and in thyroid storm the symptoms and physiologic effects of having excessive thyroid hormones are suddenly magnified.

Physiology of thyroid hormones0:22–2:18

Normally, the hypothalamus, which is located at the base of the brain, detects low blood levels of thyroid hormones and releases thyrotropin-releasing hormone into the hypophyseal portal system - which is a network of capillaries linking the hypothalamus to the anterior pituitary.
The anterior pituitary then releases thyroid-stimulating hormone, also called thyrotropin or simply TSH. TSH stimulates the thyroid gland which is a gland located in the neck that looks like two thumbs hooked together in the shape of a “V”.
The thyroid gland is made up of thousands of follicles, which are small spheres lined with follicular cells. Follicular cells convert thyroglobulin, a protein found in follicles, into two iodine-containing hormones, triiodothyronine or T3, and thyroxine or T4.
Once released from the thyroid gland, these hormones enter the blood and bind to circulating plasma proteins. Only a small amount of T3 and T4 will travel unbound in the blood, and these two hormones get picked up by nearly every cell in the body.
Once inside the cell T­4 is mostly converted into T3, and it can exert its effect. T3 speeds up the basal metabolic rate.
So as an example, they might produce more proteins and burn up more energy in the form of sugars and fats. It’s as if the cells are in a bit of frenzy.
T3 increases cardiac output, stimulates bone resorption - thinning out the bones, and activates the sympathetic nervous system, the part of the nervous system responsible for our ‘fight-or-flight’ response.
Thyroid hormone is important - and the occasional increase is like getting a boost to fight off a hungry predator or to stay warm during a snowstorm!

Causes of hyperthyroidism2:18–3:02

Now, hyperthyroidism can happen a few different ways - all of them result in too much thyroid hormone and a hypermetabolic state, where cellular reactions are happening faster than normal.
The most common cause is Graves disease, an autoimmune disorder where B cells produce antibodies against several thyroid proteins.
These autoantibodies include thyroid-stimulating immunoglobulins, which bind to the TSH receptor on follicular cells and imitate TSH.
This results in growth of the thyroid gland and stimulates the follicular cells to produce excess thyroid hormone. Another cause is toxic nodular goiter, where one or more follicles start generating lots of thyroid hormone - in some cases it’s because of a mutated TSH receptor that inappropriately keeps these follicular cells active.

Pathology of thyroid storm3:02–4:04

Regardless of the cause of hyperthyroidism, occasionally a person can develop thyroid storm, which is when the effect of having excessive thyroid hormones is suddenly magnified.
The exact reason that this happens is unclear, but there are some proposed mechanisms. The first, is that there may be more unbound thyroid hormone in the blood which is the active form of the hormone.
The second, is that the level of unbound thyroid hormone may be unchanged, but the tissues might become more sensitive to the thyroid hormone.
Third, the body might become more sensitive to catecholamines like epinephrine or dopamine, which are part of the sympathetic nervous system.
Triggers for thyroid storm include stressors like surgery, trauma, infection, or childbirth. Other triggers are abruptly stopping treatment for hyperthyroidism or taking too much thyroid hormones, which is relevant for individuals that have hypothyroidism.
The end result is the same - a state of severe hypermetabolism - so all of the effects of excessive thyroid hormones on the body are magnified.

Symptoms4:04–4:54

The symptoms of thyroid storm are mostly an exaggerated version of the symptoms of hyperthyroidism, which include weight loss despite an increase in appetite because of the higher basal metabolic rate; heat intolerance because the body is producing more heat; and rapid heart rate, sweating, hyperactivity, anxiety and insomnia because of the effect of thyroid hormones on the sympathetic nervous system.
In thyroid storm, heat intolerance turns to fever. Hyperactivity and anxiety turn to agitation, confusion, and can go as far as seizures and coma.
Cardiovascular symptoms like tachycardia can turn into cardiac arrhythmias and high-output cardiac failure. Thyroid storm can be extremely severe and can cause death if its not quickly recognized and managed.

Diagnosis4:54–5:15

The diagnosis of thyroid storm is usually based on the severity of symptoms and can be confirmed by tests like an ECG to detect a cardiac arrhythmia.
Typically there isn’t much of a difference in thyroid hormone levels between hyperthyroidism and thyroid storm, the biggest difference is in how the hormone levels affect the various body systems.

Treatment5:15–5:51

Treatment for thyroid storm requires intensive supportive care with various medications like beta-blockers to treat symptoms, thionamides to block thyroid hormone production, as well as iodine preparations, glucocorticoids, and bile acid sequestrants.
All of these medications are aimed at reducing the amount of thyroid hormone and its effects on the body. If this approach doesn’t work, plasmapheresis can be tried - that’s where blood plasma is removed, thyroid hormone can be removed, and the remaining plasma is returned to the person.
All right, as a quick recap, thyroid storm is an acute, life-threatening complication of hyperthyroidism - where the body becomes very sensitive to the effects of excess thyroid hormone.

Review5:51–6:12

It can cause symptoms like a high fever and severe tachycardia, and because of its high mortality rate, medications like beta blockers and thionamides have to be given rapidly.