Hyperthyroidism I: Introduction

Hyperthyroidism is a type of thyrotoxicosis characterized by the thyroid gland's overproduction of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). This hormone excess increases the basal metabolic rate and enhances sensitivity to catecholamines.

Diagnosis

Diagnosis is based on clinical features and biochemical testing. It typically shows suppressed thyroid-stimulating hormone (TSH) levels below 0.4 mIU/L, with elevated free T3 and/or T4. Additional tests, including thyroid autoantibodies, TSH receptor antibodies, and radioactive iodine uptake scans, help determine the underlying cause.

Etiology

Graves’ disease is the most common cause, driven by TSH receptor–stimulating antibodies, causing diffuse thyroid enlargement and excess hormone production. Other causes include toxic multinodular goiter, toxic adenoma, struma ovarii (an ovarian tumor with active thyroid tissue) , TSH-secreting pituitary adenoma, destructive thyroiditis, excess thyroid hormone intake, and iodine or drug-induced thyrotoxicosis.

Clinical Manifestations

Hyperthyroidism affects multiple systems. Common features include weight loss with increased appetite, heat intolerance, fatigue, Cardiovascular disorders like tachycardia, palpitations, atrial fibrillation. Neurological symptoms such as tremors, anxiety, and insomnia. Patients may also have muscle weakness, warm skin, increased bowel movements, menstrual disturbances, and, in Graves’ disease, eye signs like exophthalmos and a diffuse or nodular goiter.