What does the thyroid do?
Munir: The thyroid is a gland on the lower part of the neck and it makes thyroid hormone. The thyroid hormone is important for metabolism, so it's important for all your daily bodily functions, and there are thyroid hormone receptors all over the body. These receptors are what the thyroid hormone uses to do its actions on different tissues throughout the body. For example, there are thyroid hormone receptors in the heart, and thyroid hormone, when it binds to these receptors, can make the heart beat faster or make sure it's functioning properly.
What are the most common thyroid disorders and what do they entail?
Several different things can happen. The thyroid can sometimes be overactive, and we call that hyperthyroidism. It can be underactive, or hypothyroidism. And then the thyroid can also develop nodules or bumps on it, and those often are benign but sometimes can be cancerous, so those are the different types of things that can happen.
For underactive thyroid or hypothyroidism, most commonly, it's due to an autoimmune condition. So that means your own immune system can attack the thyroid and cause it to scar up, and that causes the thyroid to make less thyroid hormone over time. Overactive thyroid also can be autoimmune. We call that Grave's disease. That's where there's an antibody that your body makes and that stimulates the thyroid to be more active.
When you're overactive—like we said, the thyroid is important for metabolism—your metabolism gets revved up. So you'll feel maybe more hot, shaky, sweaty, heart racing, losing weight, frequent bowel movements, etcetera. When your thyroid is underactive, it'll be kind of the opposite. The metabolism will slow down, so you'll feel more cold, tired, gaining weight and constipation; you might have dry skin or brittle, dry hair and things like that.
And then for nodules, people often don't feel those at all. A lot of times, we pick them up because they're getting imaging for something else, and they incidentally see a thyroid nodule. The other way is sometimes people will notice a little lump in their neck, or when the doctor's examining their thyroid, they might feel a little lump that way. For those, we use ultrasound to determine whether or not the nodule might be concerning, and then if it looks like it might be of concern, we'll do a biopsy to make sure that it's not cancerous. That's usually just done with a small needle in the office.
You mentioned autoimmunity. Do we know what might cause autoimmune-related thyroid disorders? And what are some other causes of thyroid dysfunction?
The autoimmune question is a good one; we don't always know. Some of these things tend to be familial. So if someone in the family has autoimmune thyroid disease or even other autoimmune disorders, then there's a higher likelihood than the general population that the person in question might have something like that.
For hypothyroidism, there are other causes besides autoimmunity. Sometimes people have surgery on their thyroid, for example, if they had a nodule or something and needed to get it out. Sometimes radiation to the neck [is a cause]. So, for example, sometimes people have other cancers, like head and neck cancers, and they need radiation. If the thyroid is included in that radiation field, that can cause an underactive thyroid. In some parts of the world, iodine deficiency is still a cause of hypothyroidism.
Then for hyperthyroidism or overactive thyroid, besides Grave's disease, which is an autoimmune disorder, you can have nodules that are overactive sometimes. Most of the time when you have a thyroid nodule, it doesn't make too much thyroid hormone or it doesn't really cause an underactive thyroid. But sometimes it can be what we call functioning nodules. Those can overproduce thyroid hormones, and that can cause hyperthyroidism.
Another cause is thyroiditis. That's when you have inflammation of the thyroid. That can happen after you have a viral illness or a cold. We've actually interestingly seen it after COVID quite a bit, that people can get thyroid inflammation and thyroiditis, and that can cause hyperthyroidism.
Even after the COVID vaccination, sometimes people have gotten it, and there are a lot of case reports of that. So it could be different triggers. Sometimes it's a viral illness, but it doesn't always have to be.
So those are the most common causes of hyper- and hypothyroidism.
You mentioned COVID-related thyroiditis. Do we know why that happens?
It's a little bit unclear. COVID just seems to affect so many different things in people, potentially. So why this specifically occurs in some people and not others, and why COVID does that in the first place, it's hard to say. Like I said, thyroiditis often can be preceded by a viral syndrome. Even a common cold can sometimes cause thyroiditis, and those are sometimes similar coronaviruses that can cause those conditions.
Other than family history, what are the risk factors for thyroid disorders? Who is most likely to be affected?
Family history definitely plays a big part in that. There aren't a lot of other known risk factors. Iodine in your diet—too much or too little—sometimes can cause issues.
There are certain medications that also can cause thyroid disease. One of the most common ones is one called amiodarone, which people can sometimes use for irregular heart rhythms. It has quite a bit of iodine in it, which is part of why it can cause thyroid dysfunction. There are other medications we use, for example, these newer cancer medicines, like immune checkpoint inhibitors, that can cause thyroid dysfunction. There are drugs like interferon, which we use for different inflammatory conditions.
For environmental factors, it's a little bit unclear. There might be certain dietary and environmental factors, but nothing is really well validated other than iodine. Too much or too little sometimes can cause potential dysfunction.
Why does iodine have such an effect on the thyroid?
Iodine is the main mineral that's used in the formation of thyroid hormone, so thyroid hormone is made up partly of iodine. And iodine has a lot of different effects on the thyroid beyond that. Obviously, if it's used to make thyroid hormone, if you give more iodine to somebody—say they have a nodule that's a little bit over-functioning—it can actually start to cause it to make more and more thyroid hormone because it has more substrate to do that.
Iodine also has an interesting effect that it can suppress thyroid hormone release from the thyroid. So it's used to make thyroid hormone but can also decrease its release, so sometimes it can actually decrease your thyroid hormone levels and cause hypothyroidism. It has these almost conflicting effects on some people, depending on the underlying situation of the person.
What effect can thyroid disorders have on fertility and sexual health?
It definitely can affect things like ovulation. Both hypo- and hyperthyroidism can affect fertility. So you could have a decrease in ovulation. It can also cause preterm labor.
And then it can affect the menstrual cycle. Typically with hypothyroidism, they have more bleeding, and with hyperthyroidism, there's usually less. You could have amenorrhea or skipped menstrual cycles sometimes. All of that can affect fertility.
There's actually some data that shows it can affect male factor fertility and sperm function. It seems to affect both genders, potentially.
How can thyroid disorders affect a person's overall health?
Both hypo- and hyperthyroidism, if left untreated, can cause long-term complications. Both can have extreme manifestations.
So if you have hypothyroidism and it gets very severe—and usually there's a trigger—you can get something called myxedema coma, which is a much more severe form of hypothyroidism.
Then with hyperthyroidism, you can get something called thyroid storm, again, a very severe manifestation, usually in untreated disease. And usually, there's another trigger, like you had a viral infection or something like that.
In general, if you don't treat these conditions, they can cause other metabolic consequences; so for hypothyroidism, weight gain, which can potentially lead to other metabolic issues. Your cholesterol can be high, so that could possibly precipitate an increased risk for heart disease. And then your heart itself will not function as well. As I mentioned, the heart has thyroid hormone receptors. So if you don't have enough thyroid hormone, you could get almost a low-output heart failure. And then you can get an effusion, fluid building around the heart—we call that a pericardial effusion—things like that.
And with hyperthyroidism, you can get issues with the heart as well, because it'll cause increased rapidity of heart rate, and you can get kind of like a heart failure from that long term. Hyperthyroidism can also increase your risk of arrhythmias, or irregular heartbeats. And then it increases bone turnover, which can increase your risk of osteoporosis or low bone mass.
Both ways, it's important to treat so you can prevent these long-term complications.
How are thyroid disorders typically diagnosed?
A lot of times, people will have symptoms one way or the other. Blood tests are the main way we diagnose either overactive or underactive thyroid. The tricky part is the symptoms are often not really specific. So you could have fatigue, but a million things can cause fatigue. So you have to do the blood test to ensure it's a thyroid problem and not something else.
For thyroid nodules, we typically use an ultrasound to get a better sense of what the nodules look like, how big they are and where they are. After that, we'll decide whether or not we need to do a biopsy.
Are thyroid conditions curable? How are they usually treated?
Hypothyroidism is usually not curable but very treatable, depending on the reason. If it's iodine deficiency, you could maybe cure it by taking more iodine. But if it's autoimmune, it rarely just gets better. You usually need long-term thyroid hormone replacement therapy. And the same if it's been surgically removed; you'll need long-term thyroid hormone replacement therapy.
For hyperthyroidism, there are three main treatment approaches. You can use medication. We can use something called radioactive iodine, which is radiation, which is given as a pill. So basically, it's an isotopal iodine that's radioactive and can cause thyroid hormone destruction or thyroid gland destruction. Then the third option is surgery.
So it depends on the cause, and we also have a very informed discussion with the patient in terms of the pros and cons of each approach.
For hyperthyroidism, depending on what's going on, you could almost use all three approaches for most different reasons for hyperthyroidism. The only exception is thyroiditis. That's due to inflammation, so it's not like you're making more thyroid hormone. What's happening is the gland is inflamed, so you just release all the hormones you have into the blood and that causes hyperthyroidism. But that usually is short-lived, so it gets better on its own in most cases, usually in a few weeks to months. It lasts a few months sometimes in some people. For that, we just give supportive care. If they don't have many symptoms, then we don't have to even treat it at all.
If they have a lot of pain in the neck, we'll use anti-inflammatories. [We use] either nonsteroidal anti-inflammatories like ibuprofen or, in more severe cases, sometimes we'll use steroids. And then we use beta blockers, which are medicines that help kind of control if you have a high heart rate or shakiness or some of the symptoms you get from hyperthyroidism.
When should someone see a doctor and who should they see?
Most of the time, primary care [providers] can diagnose it and do the testing to rule out thyroid disease. If the case is more severe, or often in the case of hyperthyroidism, they often will refer the patient to an endocrinologist because the treatment options are a little bit more varied.
For hypothyroidism, you usually put them on replacement therapy with levothyroxine. A lot of those people are managed by their primary care physician. For hyperthyroidism, since there are more treatment options, treatments can be a little bit more complicated in a sense. Usually, an endocrinologist gets involved and helps.