Thyrotoxicosis

Excerpt

Thyrotoxicosis is a clinical condition characterized by excessive thyroid hormone activity, primarily T₃ and T₄, regardless of the underlying cause. While often confused with hyperthyroidism, the latter specifically refers to a form of thyrotoxicosis, involving excessive hormone production by the thyroid gland. Other causes of thyrotoxicosis include but are not limited to, Graves disease (where autoantibodies bind to and stimulate the thyroid-stimulating hormone [TSH] receptor), thyroiditis (which releases hormones from damaged thyroid tissue), toxic nodules and multinodular goiter (where autonomous nodules produce hormones), and iatrogenic or factitious thyrotoxicosis due to exogenous hormone intake. If left untreated, thyrotoxicosis can result in serious complications such as cardiovascular dysfunction, osteoporosis, and, in severe cases, thyroid storm—a life-threatening emergency.

The clinical presentation of thyrotoxicosis ranges from asymptomatic cases to the life-threatening condition of thyroid storm. Common symptoms stem from the hypermetabolic state caused by excess thyroid hormones and include weight loss, heat intolerance, and palpitations. A comprehensive medical history, thorough physical examination, and appropriate laboratory and imaging studies are essential to establish the differential diagnosis and determine the underlying cause for effective treatment.[2]

The thyroid gland is a butterfly-shaped organ located in the lower front of the neck. The thyroid gland regulates metabolism by producing and releasing thyroid hormones. The thyroid consists of 2 lobes connected by an isthmus and primarily produces T₃ and T₄, which regulate metabolic processes in nearly all body tissues. Thyroid-stimulating hormone (TSH), released by the anterior pituitary gland, stimulates the release of triiodothyronine (T₃) and thyroxine (T₄). In thyrotoxicosis, the balance of hormone production and release is disrupted, causing elevated circulating levels of T₃ and T₄ and triggering a hypermetabolic state.[3]

Natural History

The natural course of thyrotoxicosis varies depending on the underlying cause. In cases of hyperthyroidism, such as in Graves disease, the condition typically progresses with persistent overproduction of thyroid hormones if left untreated. In other cases, such as thyroiditis, the condition may be self-limiting, with an acute phase followed by recovery as inflammation resolves. However, without intervention, thyrotoxicosis can lead to significant systemic complications, including neuropsychiatric symptoms such as anxiety and cognitive impairment.

Thyrotoxicosis can have widespread systemic effects due to the extensive influence of thyroid hormones on various organs. The cardiovascular system is especially vulnerable, with an increased risk of tachycardia, atrial fibrillation, heart failure, thromboembolic events, and cardiovascular collapse.[2] Additionally, excessive thyroid hormones can also impact bone metabolism, leading to accelerated bone loss and osteoporosis, as well as the nervous system, causing symptoms such as tremors, anxiety, and, in severe cases, delirium during thyroid storm. Recent studies have also identified thyrotoxicosis as a risk factor for cognitive disorders in patients aged 65 or older. Identifying and addressing the underlying cause of thyrotoxicosis is essential for effectively managing its systemic effects.