If you have not had your thyroid gland surgically removed or ablated there is only one cause of hypothyroidism, and the fancy medical name for this is Hashimoto’s disease (named after Dr. Hashimoto, who first described the disease). It comes from our body’s immune system – what we use to fight infection. The immune system makes antibodies against specific infections. Those antibodies typically stay with us for a long time. If the infection comes back they immediately attack it. Sometimes our immune system accidentally makes antibodies against parts of our own body. We call this autoimmune. There are many different autoimmune diseases. You may have heard of rheumatoid arthritis or lupus. (These are some of the more nasty ones.) Autoimmune thyroid disease is when you accidentally make antibodies against the thyroid gland. In the case of Hashimoto’s disease those antibodies attack the thyroid gland. This causes inflammation in the gland (Hashimoto’s thyroiditis) and destroys it, causing hypothyroidism. Typically the thyroid gland does not recover and the hypothyroidism is permanent. Sometimes the thyroiditis will cause stored up hormone to spill out of the gland. This can cause a temporary hyperthyroidism (high thyroid level), which typically progresses to hypothyroidism.
Hashimoto’s disease is very common. Reports have found incidence in 0.3 to 2% of populations. It’s over 5 times more common in women than in men. It does tend to run in families so if you have a family history of hypothyroidism you should get screened (with a TSH blood test) periodically.
The typical symptoms of hypothyroidism are fatigue, sluggishness, “foggy” brain, depression, cold intolerance, dry skin, brittle hair and nails, depression, weight gain, constipation, and muscle aches. There are many other possible, less “textbook” manifestations that can be experienced. Everyone’s body is different in how we respond to abnormal thyroid levels. Some people will be very symptomatic and others not at all. Some people will have certain manifestations and others will have totally different ones. Keep in mind that any of the above listed symptoms can occur without hypothyroidism. They are not very specific to hypothyroidism.
How do we treat it?
Unfortunately there is nothing we can do to stop the antibodies that cause Hashimoto’s disease. All we can do is replace the missing thyroid hormone when it becomes low. We typically use a pill made with T4, which is thyroid hormone. Your body then knows what to do with it. The generic name for the T4 pill is levothyroxine (some brand names include Synthroid and Levoxyl). We follow your TSH blood test and adjust the T4 dose until it is normal. Sometimes we may add T3, which is the other form of thyroid hormone. The goal is to optimize your thyroid level without overdosing you or causing you harm. This requires assessing your symptoms alongside the blood test results.