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By Alan R Gaby
Abstract
Evidence is presented that many people have hypothyroidism undetected by conventional laboratory thyroid-function tests, and cases are reported to support the empirical use of Armour thyroid. Clinical evaluation can identify individuals with sub-laboratory hypothyroidism who are likely to benefit from thyroid-replacement therapy. In a significant proportion of cases, treatment with thyroid hormone has resulted in marked improvement in chronic symptoms that had failed to respond to a wide array of conventional and alternative treatments. In some cases, treatment with desiccated thyroid has produced better clinical results than levothyroxine. Research supporting the existence of sub-laboratory hypothyroidism is reviewed, and the author's clinical approach to the diagnosis and treatment of this condition is described.
"Objections to the Use of Armour Thyroid
The main objections voiced in textbooks and editorials 1,73 regarding the use of desiccated thyroid are: (1) its potency varies from batch to batch, and (2) the use of T3-containing preparations causes the serum T3 concentration to rise to supraphysiological levels.
Regarding between-batch variability, there may have been some problems with quality control a half-century or more ago, and in a 1980 study a number of generic versions of desiccated thyroid were still found to be unreliable in their potency. The amounts of T4 and T3 in Armour thyroid, on the other hand, were found to be constant.74
Moreover, two-year old tablets of Armour thyroid contained similar amounts of T4 and T3 as did fresh tablets. Three studies are typically cited to support the contention that T3 containing preparations should not be used. Smith et al reported a levothyroxine-plus-T3 product caused adverse side effects in 46 percent of patients; whereas, side effects occurred in only 10 percent of those receiving levothyroxine alone.75
In that study, however, the combination product and the levothyroxine product differed substantially in potency. For the combination treatment, each 100 mcg of levothyroxine was replaced by 80 mcg of levothyroxine plus 20 mcg of T3. Considering 20mcg of T3 is equivalent to 80 mcg of levothyroxine, the total hormone dose in the combination product was 60-percent greater than that in the levothyroxine preparation. Therefore, the high incidence of adverse side effects may not have been due to the T3, but to the higher total dose of thyroid hormones.
In the second study, by Surks et al, the administration of T3-containing preparations to
hypothyroid patients caused the plasma T3 concentration to become markedly elevated for several hours after ingestion of the medication.76
In most cases, however, the amount of T3 administered (50-75 mcg) was considerably greater than that contained in a typical dose of desiccated thyroid (9 mcg T3 per 60 mg),77 and/or the total dose of thyroid hormones given was excessive (180 mcg of levothyroxine plus 45 mcg of T3).
By contrast, in a patient given 60 mg of desiccated thyroid, the plasma T3 concentration increased from a hypothyroid level to a euthyroid level. Of two hypothyroid patients treated with 120 mg per day of desiccated thyroid, one showed a relatively constant plasma concentration of T3.
In the other patient, the T3 level increased by a maximum of 80 percent, to the bottom of the range seen in hyperthyroid patients, and returned to the baseline value within 24 hours. In that patient, the pre-dose plasma T3 concentration was near the top of the normal range, suggesting that this patient may have been receiving too high a dose of desiccated thyroid.
Finally, Jackson and Cobb reported that the serum T3 concentration (measured 2-5 hours
after a dose) was above normal in most patients receiving desiccated thyroid.2 They concluded there is little use for desiccated thyroid in clinical medicine. Most of the patients (87.5%) in that study, however, were taking a relatively large dose of desiccated thyroid (120-180 mg daily).
Moreover, 57.5 percent of the patients were not being treated for hypothyroidism, but rather to suppress the thyroid gland. Nearly half of the patients continued to have an elevated serum T3 concentration after they were switched to levothyroxine, even though the equivalent dose was reduced in 62.5 percent of patients.
Thus, the elevated serum T3 concentrations found in this study can be explained in large part by the high doses used and by the selection of patients, the majority of whom
were not hypothyroid. What this study does suggest is that desiccated thyroid should not be used for thyroid-suppression therapy.
Although the oral administration of T3 causes a transient increase in serum T3 concentrations, that fact does not appear to be of significance for hypothyroid patients receiving usual replacement doses of Armour thyroid. In this author's experience, reports of post-dose symptoms of hyperthyroidism are extremely rare, even among patients taking larger doses of desiccated thyroid.
An occasional patient reports feeling better when he or she takes Armour thyroid in two divided doses daily. The nature of that improvement, however, is usually an increase in effectiveness, rather than a reduction in side effects.
For patients taking relatively large amounts of desiccated thyroid (such as 120 mg daily or more), splitting the daily dose would obviate any potential concern about transient elevations of T3 levels. In practice, however, splitting the daily dose is rarely necessary."
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