TRH-Stimulation Testing [Q&As are placed in reverse chronological order. In other words, the latest Q&As come first. Earlier ones are further down the page.]

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April 12, 2000
Question: Mary Shomon recommended your website for information on problems with the conversion of thyroid hormone. I have most of the symptoms on a checklist for hypothyroidism. Interestingly, two doctors told me that some of my symptoms are fibromyalgia, but they don’t know the cause of my other symptoms. To me, all the symptoms could be hypothyroidism or the problem converting T4 to T3 that Dr. Dennis Wilson writes about. Hypothyroidism is common in my family. However, my doctor has ordered TSH and T4 levels twice, and both times the levels were normal. Since my lab tests are normal, does this mean my "hypothyroid"symptoms are caused by a conversion problem?

Dr. Lowe: No—the clinical picture you describe (normal TSH and T4 levels in someone with hypothyroid-like symptoms) does not necessarily point to a problem in converting T4 to T3. In fact, it is highly unlikely that impaired conversion is the problem. Instead, you may be hypothyroid despite normal TSH and T4 test results. Bear in mind the definition of hypothyroidism: lower-than-normal blood levels of thyroid hormone due to an underactive thyroid gland. Our TSH and thyroid hormone levels vary during the day and from day-to-day during the week. It’s possible that when you were tested, your TSH and T4 levels were within the normal range, but that the levels are abnormal at other times. As a result, on average, your tissue may have too little stimulation by thyroid hormone. Also, recent evidence suggests that the so-called "normal" ranges may be too wide. As a result, some people’s doctors may believe their test results are normal when in fact the patients are hypothyroid.

In addition, you might have central hypothyroidism. In central hypothyroidism, the thyroid gland is underactive. As a result, the blood level of thyroid hormone is too low, at least part of the time. But the cause of the underactive thyroid gland and low thyroid hormone level is not an abnormality of the thyroid gland. Instead, the cause is a dysfunction of the pituitary gland or hypothalamus. When a patient’s standard thyroid test results are normal, the doctor should always consider the possibility of central hypothyroidism. The best way to test for this form of hypothyroidism is the TRH stimulation test. With this test, we identify many patients who’re hypothyroid, although their standard thyroid test results are normal.

Some patients do have impaired conversion of T4 to T3. However, the available scientific evidence suggests that at the longest, impaired conversion lasts only a few weeks. I know of no scientific evidence supporting Dr. Dennis Wilson’s speculation that some patients have chronically impaired conversion of T4 to T3. When patients have impaired T4 to T3 conversion, they also have a predictable pattern of lab test results. However, despite extensive testing, one other researcher and I have never found this predictable lab test pattern in fibromyalgia outpatients.

Continued at top of right column . . .

 

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