The Thyroid Demystified: Time to have it checked?


by Rebecca Shatsky, MD 2011 | shatsky@myhousecallmd.com

We hear it all too often, “No, the weight gain wasn’t my fault.  My doctor told me I have a gland problem!”  Seems like a reasonable explanation right?  Mass media around the globe continues to remind you that hormones are involved in weight loss and that glands make hormones so…who cares if I haven’t hit the gym in six months and the pizza place knows me by name.  It has to be my glands that caused me to gain a few pounds last winter, right?

While “glandular problem” is not the technical term, colloquially when someone says they have a glandular problem they are most commonly referring to an underactive thyroid.  In medical-ese we call this hypothyroidism. While it’s usually not a life-threatening condition, hypothyroidism is a fairly common disease that brings with it a variety of negative symptoms including excess fatigue, dry skin, cold intolerance and weight gain (i.e. symptoms that can make you miserable).  Conversely, if your thyroid is overactive, you may develop the opposite symptoms: heart palpitations, anxiety, weight loss and heat intolerance.  What’s amazing about this underappreciated organ is that it can be easily checked with a simple blood test at your doctor’s office and any abnormalities can often be kept at bay with a simple medication.  Before you go running off to your doctor, it’s important to understand what the thyroid gland is and how it works.

What is the Thyroid?

The thyroid is a small butterfly-shaped structure that sits on the neck below the thyroid cartilage (in men we call this cartilage the Adam’s apple).  Its primary function is to release the hormones triiodothyronine and thyroxine (T3 and T4 for short).  Thyroid hormones act on nearly every cell in the body and are essential for proper development during fetal life. They increase your basal metabolic rate, influence heat genesis and regulate carbohydrate, fat, protein, and vitamin metabolism.  Both hormones are derived from iodine and, before the addition of iodinized salt to the American diet, thyroid dysfunction due to lack of iodine was fairly common.  The production and release of hormones from the thyroid gland is tightly regulated by the hypothalamus and the pituitary gland in the brain. The hypothalamus begins the chain of command by producing a hormone called thyroid releasing hormone (TRH) which stimulates the pituitary to produce and release its hormone, thyroid stimulating hormone (TSH).  Thyroid stimulating hormone, as you might suspect, then simulates the thyroid to produce T3 and T4.  While the entire hypothalamus-pituitary-thyroid axis is fairly complex, TSH remains the most sensitive measure of overall thyroid function.  When TSH levels are too high, it tells us that the thyroid gland is underactive and additional thyroid hormone supplementation might be necessary. Similarly, extremely low TSH levels can indicate an overactive thyroid and warrants further investigation as well.

What Causes Thyroid Dysfunction?

As mentioned briefly above, thyroid disorders come in two basic flavors, the under active (a.k.a. hypothyroidism) and the overactive (a.k.a. hyperthyroidism). There are a whole host of diseases that can affect the thyroid but the most common thyroid disease is an autoimmune disorder called Hashimoto’s thyroiditis (also known as chronic lymphocytic thyroiditis).  In Hashimoto’s, the body develops antibodies against the thyroid gland, which attack the cells that produce thyroid hormones and prevent normal production and release of T3 and T4 into the blood stream (in the picture to the right, the large pink cells are the normal thyroid cells we would expect to find in the thyroid.  The small blue cells peppered all over the image are immune cells invading the normal thyroid tissue…not normal).  Hashimoto’s falls into the spectrum of autoimmune diseases and leads to hypothyroidism thus the disease can initially present with fatigue, weight gain, dry skin, depression, menstrual irregularities, decreased tolerance for cold weather; all very non-specific symptoms.  The disease primarily affects women, especially after the age of 55, but it can affect both genders and all age groups.  You may be at greater risk for thyroid disease if you suffer from other autoimmune diseases including Type 1 Diabetes, Addison’s disease, vitiligo or if you have family history of thyroid disease.  Hypothyroidism is treated by replacing your thyroid hormone with a daily thyroid hormone pill.

On the other end of the spectrum are diseases that cause hyperthyroidism, the most common of which is an autoimmune disease called Grave’s disease.  In Grave’s disease, the body produces antibodies that mimic TSH and stimulate the cells of the thyroid to produce excessive amounts of thyroid hormones (instead of attacking these cells like in Hashimoto’s thyroitidis).  Hyperthyroidism can also occur when the thyroid develops a nodule that begins to independently overproduce thyroid hormones.  These nodules are not generally cancerous, but need to be treated to control the symptoms of hyperthyroidism, which can include weight loss, anxiety, heat intolerance, increased heart rate, palpitations and excessive sweating.  Untreated Grave’s disease patients can even develop a condition where their eyes are pushed slightly out of the socket and literally look like they are bugging out of the head. We call this exophthalmos.

Random Fact: George H. and Barbara Bush were both diagnosed with Grave’s disease.

In both hypo- and hyperthyroid states, it is possible to develop a goiter (an unsightly, painless enlargement of the thyroid due to constant stimulation of the gland).  If your doctor has ever asked you to swallow while touching your neck, this is one of the conditions they were checking for.  Most goiters develop slowly over decades and the majority occur because the thyroid is not producing enough thyroid hormone (in hypothyroidism).  With a goiter, thyroid cells are stimulated by the pituitary and attempt to make thyroid hormone but are unable to finish the job for a number of reasons.  The end result is a large, underactive gland. In Grave’s disease however, a goiter develops because the entire thyroid gland is over-stimulated and actively producing tons of thyroid hormone.  In the US, the most common cause of goiter is autoimmune thyroiditis.  In many developing countries (where people have inadequate intake of iodine), iodine deficiency can lead to enormously large goiters that cause hoarseness and shortness of breath by compression of the airway and nerves of the surrounding area.

When Should I Have My Thyroid Checked?

In most people, the thyroid sits quietly in its home on the neck producing hormones without ever letting you know it’s there.  However, the thyroid is an elusive organ.  Thyroid dysfunction can creep up on us slowly, making it hard for patients to identify.  With symptoms as non-specific as weight gain and dry skin, hypothyroidism is easy to miss. Recent data estimates that autoimmune hypothyroidism affects 1/200 female patients and that some form of thyroid dysfunction may be present in up to 10% of women (1).  Checking your thyroid hormones is not a part of routine health screening like cholesterol or blood sugar, so if you think you are experiencing any of the symptoms of thyroid disease (either hyper- or hypo-) mentioned above, be sure to tell your doctor so that they can check your TSH level.  Screening is especially important in pregnant women because even subclinical hypothyroidism can affect pregnancy outcomes and the health of the baby (3).  The test is fairly inexpensive, available almost everywhere and, most importantly, could make a world of difference in your health.

Questions? E-mail the Author: shatsky@myhousecallmd.com

References

  1. Canaris GJ, Manowitz NR, Mayor G, et al. The Colorado Thyroid Disease Prevalence Study. Archives of Internal Medicine.
  2. Danese MD, Powe NR, Sawin CT, et al. Screening for Mild Thyroid Failure at the Periodic Health Examination: A Decision and Cost-Effectiveness Analysis. JAMA. 1996;276:285-92.
  3. McDermott, Michael., Laine, Christine., Williams, Sankey., Turner, Barbara., In the Clinic: Hypothyroidism. Annals of Internal Medicine. 2009. Dec; 1-16
  4. Autoimmune Thyroid Disease: A Systematic Review of the Literature. Clinical Endocrinology. 2008. 69: 687-696.
  5. Screening for Thyroid Disease: Recommendation Statement. Annals of Internal Medicine. 2004;140:125-7. 2000;160:526-34.

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