Hyperthyroidism
Also known as: overactive thyroid, thyrotoxicosis
Hyperthyroidism is a condition in which the thyroid gland produces excess thyroid hormone, accelerating the body's metabolism. Common findings include weight loss, heat intolerance, tremor, and rapid heartbeat; Graves disease is the most frequent cause.
Hyperthyroidism is overproduction of thyroid hormone by the thyroid gland. Because thyroid hormones (T3 and T4) set the body's metabolic pace, excess hormone pushes nearly every system into overdrive: patients lose weight despite a good appetite, feel hot and sweaty, and develop tremor, anxiety, insomnia, palpitations, and a rapid or irregular heartbeat.
The most common cause is Graves disease, an autoimmune disorder in which stimulating antibodies bind the TSH receptor and drive the gland continuously. Graves disease can add findings not caused by hormone excess alone, including exophthalmos (bulging eyes) and pretibial myxedema. Other causes include toxic multinodular goiter, a solitary hyperfunctioning ("hot") nodule, thyroiditis that transiently releases stored hormone, and excess thyroid hormone ingestion.
Laboratory diagnosis rests on the pituitary feedback loop: in primary hyperthyroidism, TSH is low while free T4 (and often T3) is high, because the pituitary suppresses its signal in response to hormone excess. Treatment approaches include antithyroid drugs that block hormone synthesis, beta blockers for symptom control, radioactive iodine ablation, and thyroidectomy. Untreated severe disease risks thyroid storm — an abrupt, life-threatening surge of hormone activity.
Hyperthyroidism appears across licensing exams. The USMLE Step 1 tests causes, autoantibodies, and lab patterns; the PTCE covers thyroid drug classes within endocrine medications; and the NPTE-PTA includes it among endocrine and metabolic conditions relevant to therapy. Anchor your studying to the low-TSH, high-T4 pattern and the Graves disease presentation.
Key takeaways
- Hyperthyroidism is excess thyroid hormone production, producing a hypermetabolic state.
- Hallmark symptoms include weight loss, heat intolerance, tremor, anxiety, and tachycardia.
- Graves disease — TSH-receptor-stimulating antibodies — is the most common cause and can add exophthalmos.
- Labs show low TSH with elevated free T4 in primary disease.
- The USMLE Step 1, PTCE, and NPTE-PTA all test hyperthyroidism from their respective angles.