Thyrotoxicosis is a clinical state of inappropriately high levels of circulating thyroid hormones (T3 and/or T4) in the body from any cause.

It is often incorrectly used interchangeably with hyperthyroidism, which is a form of thyrotoxicosis caused by excessive endogenous thyroid hormone production.

The clinical presentation varies, ranging from asymptomatic or subclinical, to life-threatening thyroid storm. Typical symptoms are due to the hypermetabolic state induced by excess thyroid hormones and include weight loss, heat intolerance, and palpitations. The differential for thyrotoxicosis is broad and will need a combination of a thorough physical exam, laboratory studies, and imaging to determine the underlying etiology for appropriate treatment. If not adequately treated, thyrotoxicosis can lead to serious complications including delirium, altered mental status, osteoporosis, muscle weakness, atrial fibrillation, congestive heart failure (CHF), thromboembolic disease, cardiovascular collapse, and death .

Refrences : https://www.ncbi.nlm.nih.gov/books/NBK482216/