Hyperthyroidism

Hyperthyroidism, or an overactive thyroid, means the thyroid gland in the front of the neck releases too much of its hormones, thyroxine (T4) and triiodothyronine (T3). These hormones set the pace of metabolism in almost every tissue, so an excess speeds the whole body up. Normally the pituitary gland controls their output with thyroid-stimulating hormone (TSH), in a negative feedback loop that turns TSH down as thyroid hormone levels rise.

The most common cause is Graves' disease, an autoimmune condition where antibodies imitate TSH and drive the gland nonstop; it can also make the eyes bulge. Other causes include overactive lumps called nodules, thyroiditis, in which an inflamed gland leaks its stored hormone, too much iodine, and taking too much thyroid hormone medicine. Typical signs are a fast or irregular heartbeat, weight loss despite a good appetite, feeling hot and sweaty, a shaky hand tremor, anxiety, poor sleep and sometimes a goiter, a swollen thyroid. Left untreated, it can lead to atrial fibrillation, heart failure and thinning bones.

Blood tests show a low TSH with high T4 or T3, and a radioactive iodine uptake scan helps find the cause. Treatment uses antithyroid drugs that block hormone production, radioactive iodine that destroys overactive tissue, or surgery, often with a beta blocker to calm symptoms in the meantime.