The short answer: Thyroid storm is a rare, life-threatening surge of thyroid hormone effects, usually in someone with untreated or poorly controlled hyperthyroidism. Warning signs include high fever, a racing heart, agitation or confusion, vomiting, and diarrhea. A 2019 U.S. study in Thyroid found storm carried a 12-fold higher hospital death rate. Call 911.
What exactly is thyroid storm?
Thyroid storm is the most extreme form of thyrotoxicosis, the state of having too much thyroid hormone acting on the body. The 2016 Japan Thyroid Association and Japan Endocrine Society guideline defines it as an endocrine emergency marked by multiple organ failure from severe thyrotoxicosis, often set off by another illness. Other names include thyrotoxic crisis and thyroid crisis, per MedlinePlus.
Most cases happen in people with Graves' disease, which NIDDK lists as the most common cause of hyperthyroidism. Storm can also come from toxic nodules, thyroiditis, or taking too much thyroid hormone medicine, according to the JTA guideline. If you want the basics of the underlying condition first, see our guide to hyperthyroidism symptoms and treatment.
It is rare. A national U.S. inpatient study covering 2004 to 2013 estimated 0.57 to 0.76 cases per 100,000 people per year. Among 121,384 hospital discharges for thyrotoxicosis, 19,723 (16.2%) were coded as thyroid storm.
What warning signs can a patient or family see?
The key pattern is hyperthyroid symptoms that suddenly become severe and start to affect the brain, heart, and gut. MedlinePlus lists these symptoms:
- Fever: a high body temperature, often with heavy sweating.
- Racing or pounding heart: a very fast pulse, sometimes irregular.
- Mental changes: agitation, restlessness, confusion, or a change in alertness.
- Gut symptoms: diarrhea, and in hospital criteria, nausea and vomiting.
- Shaking and bulging eyes in people with Graves' disease.
Families often notice the mental changes first. The JTA criteria give brain symptoms extra weight because they point to storm more strongly than other organ signs. Yellowing of the skin or eyes (jaundice) and shortness of breath are late, serious signs of liver and heart strain. Anxiety and a fast heartbeat on their own are common in ordinary hyperthyroidism. Our article on thyroid anxiety and panic attacks explains that milder overlap, and anxiety.md covers panic symptoms that are not thyroid-related.
What usually triggers thyroid storm?
Storm rarely appears out of nowhere. Burch and Wartofsky wrote in 1993 that most cases follow a precipitating event or another illness. Known triggers from MedlinePlus and the JTA guideline include:
- Stopping antithyroid medicine suddenly, or missing doses. This was the most common trigger in the Japanese nationwide surveys.
- Infection, which is a frequent stressor.
- Trauma, a heart attack, or surgery, including non-thyroid surgery.
- Thyroid surgery or radioactive iodine in someone whose thyroid levels are not yet controlled.
- Exposure to a large amount of iodine in a person with hyperthyroidism.
- Taking too much thyroid hormone medicine.
- Some drugs, including amiodarone and the cancer drugs sorafenib and ipilimumab.
MedlinePlus notes that storm after radioactive iodine is rare but can occur a week or more after treatment. Our guide on what to expect after radioactive iodine covers that recovery window. The JTA guideline also reports that about 20% of storms in Japan began in people whose Graves' disease had never been diagnosed.
Why is thyroid storm a 911 emergency?
Thyroid storm can turn fatal quickly, often through the heart. MedlinePlus warns that abnormal heart rhythms, heart failure, and fluid in the lungs can develop rapidly and cause death. It advises anyone with hyperthyroidism and storm symptoms to call 911.
The numbers support that advice. In the Japanese nationwide survey of 356 patients, published in 2012, mortality was 11.0% for definite storm and 9.5% for suspected storm. Multiple organ failure was the most common cause of death. In the U.S. data, hospital death rates were 1.2% to 3.6% with storm versus 0.1% to 0.4% without it. Earlier care makes a difference: Burch and Wartofsky described fatality rates of 20% to 50% in the series of their era.
How do hospitals diagnose thyroid storm?
No single blood test confirms thyroid storm. In the Akamizu survey, free T4 and free T3 levels were similar in patients with storm and in thyrotoxic patients without storm. So doctors judge severity by how the organs are responding. Blood tests still matter: they confirm thyrotoxicosis and check the heart, kidneys, liver, and infection, per MedlinePlus. Our page on thyroid blood tests explains TSH, free T4, and T3.
Two scoring systems are in common use, both described in the 2016 JTA guideline:
- Burch-Wartofsky Point Scale (BWPS), 1993. Points are added for temperature, heart rate, atrial fibrillation, heart failure, gut or liver problems, brain symptoms, and a known trigger. A total of 45 or more suggests thyroid storm. A score of 25 to 44 suggests impending storm. Under 25 makes storm unlikely.
- Japan Thyroid Association criteria, 2012. Thyrotoxicosis with high free T3 or free T4 is required. Doctors then look for a set combination of brain symptoms, fever of 38°C or higher, heart rate of 130 or higher, heart failure, and gut or liver signs (including bilirubin of 3.0 mg/dL or higher). Cases are graded as definite (TS1) or suspected (TS2).
The JTA guideline recommends using both systems together. It also says that if doctors cannot tell whether a symptom comes from the trigger or from storm, they should count it toward storm.
How is thyroid storm treated?
Treatment usually happens in an intensive care unit and attacks the problem from several sides at once. The JTA guideline recommends a combined approach, and MedlinePlus describes the same pieces in outline:
- Antithyroid medicines (thionamides) to stop new hormone production.
- Iodine, given alongside antithyroid medicine, to block hormone release.
- Beta-blockers, often by IV, to slow the heart and blunt hormone effects.
- Corticosteroids in many cases.
- Cooling, fluids, oxygen, and treatment of the trigger, such as antibiotics for infection.
Guideline-based care seems to help. A 2024 Japanese registry study of 110 patients found 30-day mortality of 5.5%, about half the 10.7% seen in the earlier survey. After recovery, the JTA guideline advises considering radioactive iodine or surgery to prevent a repeat storm. The 2016 American Thyroid Association guideline is the main U.S. reference for managing hyperthyroidism overall.
When should you go to the ER? A checklist
Call 911 or go to the nearest emergency department if a person with known or suspected hyperthyroidism has any of these. The list is built from MedlinePlus and the JTA criteria:
- Fever of 38°C (100.4°F) or higher with a racing heart.
- Confusion, unusual sleepiness, agitation that will not settle, or a seizure.
- A resting pulse that feels very fast, pounding, or irregular.
- Shortness of breath, swelling, or chest pain.
- Repeated vomiting or diarrhea, or yellowing of the skin or eyes.
- Any of the above within days of stopping antithyroid medicine, surgery, an infection, or radioactive iodine.
Bring a list of medicines, recent thyroid lab results, and the name of the treating endocrinologist. Tell the ER team about the thyroid condition right away.
The bottom line
Thyroid storm is rare, but it is a true emergency. Watch for fever, a racing heart, confusion, and vomiting or diarrhea in anyone with hyperthyroidism, especially after a trigger. Do not wait it out: call 911. The best prevention is steady treatment of hyperthyroidism and never stopping antithyroid medicine without talking to your doctor.
Last updated: November 2026. This article is for informational purposes only and does not constitute medical advice. If you think someone has thyroid storm, call 911 or your local emergency number now.