In an older adult, an overactive thyroid can look like depression

The thyroid is a small butterfly-shaped gland at the front of the neck, and
the hormones it makes set the rate at which the body uses energy. They reach
nearly every organ: breathing, heart rate, weight, digestion, mood.
Hyperthyroidism is that gland making more than the body needs, and untreated
it damages the heart, bones, muscles, menstrual cycle and fertility.

The symptoms, and the inversion after 60

In a younger adult everything speeds up: nervousness or irritability, fatigue,
muscle weakness, trouble tolerating heat, trouble sleeping, a tremor usually
in the hands, a rapid and irregular heartbeat, frequent bowel movements or
diarrhoea, weight loss, mood swings, and sometimes a goitre — an enlarged
thyroid that makes the neck look swollen and can interfere with breathing or
swallowing.

Adults over 60 often present the opposite way. They may lose their
appetite and withdraw from other people — a picture that is mistaken for
depression or dementia. An older person who has gone quiet and stopped eating
is not obviously someone with an overactive gland, which is exactly the
problem.

Where it comes from

Risk is higher in women, over 60, within six months of a pregnancy, after
thyroid surgery or a thyroid problem such as goitre, with a family history of
thyroid disease, and alongside pernicious anaemia, type 1 diabetes or primary
adrenal insufficiency.

What it causes if left alone

An irregular heartbeat that can lead to blood clots, stroke and heart
failure. Graves' ophthalmopathy, an eye disease causing double vision,
light sensitivity and eye pain, and in rare cases vision loss. Thinning bones
and osteoporosis. Fertility problems, and in pregnancy: premature birth, low
birth weight, high blood pressure and miscarriage.

Diagnosis is a medical history and physical exam, then thyroid blood tests
(TSH, T3, T4, thyroid antibodies), and imaging where needed — a thyroid scan,
an ultrasound, or a radioactive iodine uptake test, which measures how much
of a swallowed dose the thyroid pulls out of the blood.

Treatment, including the one that aims at the opposite condition

• Antithyroid medicines make the thyroid produce less. One to two years,
  sometimes several. The simplest treatment, and often not a permanent cure.
• Beta blockers do nothing to the thyroid. They reduce tremor, rapid
  heartbeat and nervousness, quickly, while another treatment takes effect.
• Radioiodine therapy — radioactive iodine swallowed as a capsule or
  liquid, which slowly destroys the hormone-producing cells and leaves other
  tissues alone. Common and effective. **Almost everyone treated this way
  later develops hypothyroidism**, because the cells are gone. That is not a
  failure: an underactive thyroid is easier to treat and causes fewer
  long-term problems than an overactive one, so the trade is deliberate.
• Surgery is rare — for large goitres, or pregnancy where antithyroid
  medicines cannot be used. Remove the whole gland and thyroid medicine
  becomes lifelong.

One thing to manage yourself: avoid too much iodine, and ask which foods,
supplements and medicines that rules out.

*Source: National Institute of Diabetes and Digestive and Kidney Diseases,
via MedlinePlus.*