If you have a goiter, the first thing doctors will assess is whether or not your thyroid hormone levels are normal. This evaluation is discussed in detail in Chapter 2; however, simply stated, you need to know your thyroid stimulating hormone (TSH) level and your free T4 level (your thyroxine level). If your TSH level is normal, particularly if your free T4 is also normal, then your thyroid hormone status is considered normal, a condition known as being euthyroid. There are several types of goiters in euthyroid people, generally called euthyroid goiters.
The TSH is most sensitive, provided that your pituitary gland is normal. That's why a normal TSH is confirmed by the free T4. If the free T4 is low, despite a normal or low TSH, this could be a sign of a dysfunctional pituitary gland, often from a benign pituitary tumor. On the other hand, if the free T4 is very high, yet the TSH is inappropriately normal or elevated, there are two possible explanations. If you have thy-rotoxic symptoms (see Chapter 4), you may have a rare pituitary tumor that makes TSH. If you are clinically euthyroid, with no symptoms of hypothyroidism (see Chapter 3) or thyrotoxicosis, then you may have thyroid hormone resistance (discussed in Chapter 18).
If the TSH is elevated then you're hypothyroid, and it's likely that the elevated TSH itself has contributed to the growth of the goiter. Of course, the TSH is most often elevated because of Hashimoto's thyroiditis (in industrialized countries), discussed in Chapter 5, or iodine deficiency (in much of the underdeveloped world), discussed in Chapters 1 and 3. Adequate thyroid hormone replacement reduces TSH levels to normal and often reduces the size of the goiter. However, sometimes there is so much scar tissue in the thyroid that thyroid hormone treatment doesn't shrink the goiter very much.
When the TSH is suppressed because of thyrotoxicosis, a number of possibilities need to be considered. If the entire gland is generally enlarged, then the most common diagnosis is Graves' disease. (See Chapter 6.) On the other hand, the entire gland may be enlarged, containing individual thyroid nodules, many of which could be autonomous toxic nodules; this condition is called a toxic multinodular goiter.
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