Is a Thyroid Problem Causing My Fatigue?


Is a Thyroid Problem Causing My Fatigue?

Fatigue is definitely one of the symptoms of thyroid deficiency (hypothyroidism.) Thyroid hormones (T4, thyroxine and T3, triiodothyronine) regulate the metabolic processes and an insufficient amount of the hormone causes a generalized slowing of these processes, cold intolerance, weight gain, constipation, dry skin and other problems in addition to fatigue.

The best way to determine thyroid hormone deficiency is through measuring the thyroid stimulating hormone. Thyroid stimulating hormone (TSH) and thyroid hormone exist in a reciprocal relationship where a drop in the thyroid hormone level produces a rise in TSH which serves to stimulate the thyroid gland to make more thyroid hormone.

TSH is not the sole measure of thyroid status although it is often used as the solitary screen for hypothyroidism. In the event of a problem with the pituitary gland’s ability to regulate TSH an individual may have low thyroid hormone level in the setting of a low or normal TSH and the diagnosis of hypothyroidism might be missed.

Measuring thyroid hormone directly can uncover a situation as described above. In such a case thyroid hormone, measured as free T4, would be low indicating thyroid deficiency in the presence of a normal or low TSH.

Why not simply rely on a direct measurement of thyroid hormone (free T4) to screen for a hypothyroidism? A low free T4 almost always defines a low thyroid state but thyroid hormone is very precisely gauged to the individual where a particular free T4 level, although in the normal range, might be insufficient for a particular person. TSH when functioning correctly increases when the thyroid hormone drops below a specific set point even though that set point might be in the normal range for the general population.

Therefore, measuring TSH and free T4 can almost always correctly identify a hypothyroid condition. TSH alone can identify hypothyroidism 95% of the time which is why it is often used separately as a screen for thyroid disease.

However, there is a controversy about whether a normal TSH (usually 0.4 to 5.0 mU/L) is actually normal. The point of those who would reduce the TSH upper limit of normal to 2.5 mU/L is that an upper limit of 5.0 mU/L was extracted from a general population that included many people with thyroid disease thereby distorting the notion of normal. Using a population free of thyroid disease produces an upper limit of 2.5 mU/L.

To complicate matters further, TSH increases somewhat with age in the absence of anything to suggest a hypothyroid state. The upper limit of normal for patients in their eighties could be as high as 6 to 8.

There are additional tests used to define thyroid status including the T3-resin uptake and antithyroid peroxidase (anti-TPO.) The latter is usually abnormal in patients with hypothyroidism and can, if present, can predict that hypothyroidism will eventually develop.

Thyroid disease characterized by a TSH of 10 or less and a normal free T4 is termed “subclinical hypothyroidism” the treatment for which is controversial with some experts recommending no treatment and others recommending thyroid hormone supplementation.

Attempts to define symptoms have been unsuccessful although many patients have complaints suggesting hypothyroidism, including fatigue. Statistical analysis of symptoms cannot separate this group from those with normal thyroid function. Most physicians think that patients with a TSH that is less than 10, although it is in the abnormal range, do not have symptoms attributable to thyroid disease. However, I have seen patients in this category with fatigue who have definitely responded to thyroid hormone treatment.



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