In Graves' disease, antibodies impersonate a hormone and send the thyroid into overdrive
Graves' disease happens when the immune system makes antibodies that lock onto the thyroid and mimic the signal telling it to produce hormone. The gland obeys nonstop, causing racing hearts, weight loss despite hunger and, in about a quarter of patients, bulging eyes. It strikes women about 7.5 times as often as men.
Named after the Irish surgeon Robert Graves, who described it in 1835, though others had noted it before, the disease is the most common cause of an overactive thyroid, accounting for roughly half to four-fifths of cases in the United States. It affects about 3 percent of women and 0.5 percent of men, most often starting between 40 and 60. Typical effects include insomnia, tremor, sweating, heat intolerance, palpitations, diarrhoea and weight loss even with a bigger appetite.
The mechanism is a case of mistaken identity. Normally the pituitary releases thyroid-stimulating hormone, or TSH, which binds receptors on thyroid cells. In Graves' disease, antibodies bind the same receptor and keep it switched on, so the gland pumps out the hormones T4 and T3 and often swells into a goitre. The pituitary senses the flood and shuts off its own TSH, which is why blood tests typically show very high thyroid hormone and almost undetectable TSH.
Two signs point specifically to Graves' rather than other thyroid problems: protruding eyes and a thickened, orange-peel patch of skin on the shins. Both are thought to arise because antibodies attack tissues that share features with the thyroid, causing swelling behind the eyeball and inflamed skin. Why the immune system goes astray is unclear. Genes matter, since an identical twin of a patient has about a 30 percent chance of developing it, but no single responsible gene has been found. Infection, stress or childbirth may trigger onset, smoking raises the risk, and a gut bacterium once suspected as a trigger is now disputed.
There are three main treatments. Radioactive iodine, swallowed as a drink or capsule, gathers in the gland and gradually kills its tissue over a period of weeks or months, after which patients take synthetic hormone. Antithyroid drugs such as methimazole and symptom-easing beta blockers can help in the meantime, and surgery to remove the gland is the third route.
Source: Graves' disease
