Thyroid storm (thyroid crisis) is a potentially life-threatening condition for people with hyperthyroidism. Thyroid storm happens when your thyroid gland suddenly releases large amounts of thyroid hormone in a short period of time. If you have thyroid storm, you will need emergency medical treatment.

Thyroid storm is more likely to develop when a person has a serious health problem in addition to hyperthyroidism or in people who have untreated or undertreated Graves' disease. The problem usually happens after a stressful event or a serious illness, such as a major infection. It may also be triggered by surgery or by using iodine for a CT scan or in radioactive iodine therapy.

Symptoms of thyroid storm include:

• Feeling extremely irritable or grumpy.
• High systolic blood pressure, low diastolic blood pressure, and fast heartbeat.
• Nausea, vomiting, or diarrhea.
• High fever.
• Shock and delirium.
• Feeling confused.
• Feeling sleepy.
• Yellow skin or eyes.
• Symptoms of heart failure, such as breathing problems or feeling very tired.

Thyroid storm can lead to coma, heart failure, or death.