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Hypothyroidism: Overview, Causes, and Symptoms

Learn more about the what it means to have hypothyroidism and to recognize the signs before you are diagnosed.

Part 2: Hypothyroidism (Underactive Thyroid): Too Little Thyroid Hormone

Too little thyroid hormone produced.Since hypothyroidism is caused by too little thyroid hormone secreted by the thyroid, the diagnosis of hypothyroidism is based almost exclusively upon measuring the amount of thyroid hormone in the blood.

There are normal ranges for all thyroid hormones which have been calculated by computers which measured these hormones in tens of thousands of people. If your thyroid hormone levels fall below the normal range, that is consistent with hypothyroidism 

These tests are very accurate and reliable and are so routine that they are available to everybody. More about these tests on another page. However, it's not always so simple...keep reading.

The easiest way to understand this disorder is to consider its root meaning:

  • Hypo means too little
  • Thyroidism is a disease of the thyroid
  • Therefore, hypothyroidism = a disease of too little thyroid activity.

In order to determine if you have hypothyroidism, your doctor will order a thyroid function panel. This blood test measures the levels of key thyroid hormones: T4 and Thyroid Stimulating Hormone (TSH).

In a person with an underactive thyroid gland, the blood level of T4 (the main thyroid hormone) will be low, while the TSH level will be high. This means that the thyroid is not making enough hormone and the pituitary recognizes it and is responding appropriately by making more TSH in an attempt to force more hormone production out of the thyroid. 

In the more rare case of hypothyroidism due to pituitary failure, the thyroid hormone T4 will be low, but the TSH level will also be low. The thyroid is behaving "appropriately" under these conditions because it can only make hormone in response to TSH signals from the pituitary gland. 

Since the pituitary is not making enough TSH, then the thyroid gland will be unable to make enough T4. The real question in this situation is what is wrong with the pituitary?  But in the typical and most common form of hypothyroidism, the main thyroid hormone T4 is low, and the TSH level is high. 

The next question is: When is low too low, and when is high too high?  Blood levels have "normal" ranges, but other factors need to be taken into account as well, such as the presence or absence of symptoms.  You should discuss your levels with your doctor so you can interpret how they are helping (or not?) fix your problems.

Oh, if only it were this simple all the time!  Although the majority of individuals with hypothyroidism will be easy to diagnose with these simple blood tests, many millions will have this disease in mild to moderate forms which are more difficult to diagnose.  The solution for these people is more complex and this is due to several factors. 

First we must realize that not all patients with hypothyroidism are the same.  There are many degrees of this disease from very severe to very mild.  Additionally, and very importantly, we cannot always predict just how bad (or good) an individual patient will feel just by examining his/her thyroid hormone levels. 

In other words, some patients with very "mild" deviations in their thyroid laboratory test results will feel just fine while others will be quite symptomatic.  The degree of thyroid hormone abnormalities often, but NOT ALWAYS will correlate with the degree of symptoms.

It is important for both you and your physician to keep this in mind since the goal is not necessarily to make the lab tests go into the normal range, but to make you feel better as well!  We must also keep in mind that even the "normal" thyroid hormone levels in the blood have a fairly large range, so even if a patient is in the "normal" range, it may not be the normal level for them.

For the majority of patients with hypothyroidism, taking some form of thyroid hormone replacement (synthetic or natural, pill or liquid, etc) will make the "thyroid function tests" return to the normal range, AND, this is accompanied by a general improvement in symptoms making the patient feel better. 

This does not happen to all individuals, however, and for these patients, it is very important to find an endocrinologist who will listen and be sympathetic.  (We aim to help you find this type of doctor.)  Because most patients will be improved (or made completely better) when sufficient thyroid hormone is provided on a daily basis to make the hormone levels in the blood come into the normal range, physicians will often rely on test results to determine when a patient is on the appropriate dose and therefore doing well. 

Remember, these tests have a wide normal range.  Find a doctor who helps make you FEEL better, not just make your labs better because once given this diagnosis, you are likely to carry it for a long, long time.  There is more than one drug, there is more than one lab test, and there is a "just right" doctor for everybody.

Treatment of Hypothyroidism

Hypothyroidism is usually quite easy to treat (for most people)!  The easiest and most effective treatment is simply taking a thyroid hormone pill (levothyroxine) once a day, preferably in the morning. This medication is a pure synthetic form of T4 which is made in a laboratory to be an exact replacement for the T4 that the human thyroid gland normally secretes. It comes in multiple strengths, which means that an appropriate dosage can almost always be found for each patient.

The dosage should be re-evaluated and possibly adjusted monthly until the proper level is established. The dose should then be re-evaluated at least annually. If you are on this medication, make sure your physician knows it so he/she can check the levels at least yearly. 

Note:  Just like we discussed above, however, this simple approach does not hold true for everybody. Occasionally the correct dosage is a bit difficult to pinpoint and therefore you may need an exam and blood tests more frequently.  Also, some patients just don't do well on some thyroid medications but will feel better with other options. 

For these reasons, you should not be shy in discussing with your doctor your blood hormone tests, symptoms, how you feel, and the type of medicine you are taking.  The goal is to make you feel better, make your body last longer, slow the risk of heart disease and osteoporosis...in addition to making your blood levels normal! 

Sometimes that's easy, but when it's not, you need to work with a doctor who is willing to listen to you and to spend the time you need to explore different dosages and to consider other types of medications (or maybe even an alternative diagnoses).

Some patients will notice a slight reduction in symptoms within 1 to 2 weeks, but the full metabolic response to thyroid hormone therapy is often delayed for a month or two before the patient feels completely normal. It is important that the correct amount of thyroid hormone is used. Not enough and the patient may have continued fatigue or some of the other symptoms of hypothyroidism.

Too high a dose could cause symptoms of nervousness, palpitations or insomnia typical of hyperthyroidism. Some recent studies have suggested that too much thyroid hormone may cause increased calcium loss from bone increasing the patient's risk for osteoporosis.

For patients with heart conditions or diseases, an optimal thyroid dose is particularly important. Even a slight excess may increase the patient's risk for heart attack or worsen angina. Some physicians feel that more frequent dose checks and blood hormone levels are appropriate in these patients.

After about one month of treatment, hormone levels are measured in the blood to establish whether the dose of thyroid hormone which the patient is taking is appropriate. We don't want too much given or subtle symptoms of hyperthyroidism could ensue, and too little would not alleviate the symptoms completely. Often blood samples are also checked to see if there are antibodies against the thyroid, a sign of autoimmune thyroiditis. 

Remember, this is the most common cause of hypothyroidism. Once treatment for hypothyroidism has been started, it typically will continue for the patient's life. Therefore, it is of great importance that the diagnosis be firmly established and you have a good relationship with a physician you like and trust.

Synthetic T4 can be safely taken with most other medications.  Patients taking cholestyramine (a compound used to lower blood cholesterol) or certain medications for seizures should check with their physician about potential interactions.

Women taking T4 who become pregnant should feel confident that the medication is exactly what their own thyroid gland would otherwise make. However, they should check with their physician since the T4 dose may have to be adjusted during pregnancy (usually more hormone is needed to meet the increased demands of the mother's new increased metabolism).

There are other potential problems with other drugs including iron-containing vitamins. Once again, pregnant women (and all women and men for that matter) taking iron supplements should discuss this with your physician.

While Synthroid is the most common brand name thyroid hormone replacement, most people will now receive the generic version of levothyroxine tablets as the most cost-effective and usually the version that will be covered by your health insurance. 

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Symptoms of Hypothyroidism