"Sub-laboratory" hypothyroidism and the empirical use of Armour® Thyroid

Alternative Medicine Review, June, 2004 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[R] 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.

Introduction

Hypothyroidism is a common disorder in which the amount of hormone secreted by the thyroid gland is inadequate to meet the body's needs. As the main function of thyroid hormone is to stimulate metabolism, hypothyroidism results in a slower rate of metabolism and its associated manifestations. The symptoms of hypothyroidism can vary considerably from person to person. Table 1 includes a comprehensive list of symptoms. while Table 2 lists signs of hypothyroidism seen on physical exam.

If not diagnosed and treated, hypothyroidism can in some cases become severely debilitating or even fatal. Appropriate hormone-replacement therapy, on the other hand, will ameliorate the clinical manifestations of the disease, allowing most affected individuals to have a normal or close-to-normal quality of life.

In cases of overt hypothyroidism, the serum concentrations of total and free thyroxine (T4) and triiodothyronine (T3) are below normal, and the concentration of thyroid-stimulating hormone (TSH) is increased. The magnitude of the increase in TSH level is roughly proportional to the severity of the hypothyroidism. TSH is released from the pituitary gland, which helps regulate the activity of the thyroid gland through a feedback mechanism. The pituitary secretes more TSH in response to a hypothyroid state, less TSH in the euthyroid state, and even less in the face of hyperthyroidism. The secretion of TSH from the pituitary gland is further regulated by the hypothalamic hormone thyrotropin-releasing hormone (TRH), which helps control the set-point of the pituitary.

In milder cases of hypothyroidism, serum levels of T4 and T3 are often normal (although typically in the low-normal range), while the TSH level is above normal. This pattern of laboratory values, which is frequently called "subclinical hypothyroidism," suggests the thyroid gland, while being stimulated to work harder, is only just keeping up with the body's needs. Most physicians recommend thyroid-replacement therapy for patients with grossly elevated TSH levels (suggesting more pronounced hypothyroidism); whereas, the risk/benefit ratio in treating patients with only slightly increased TSH values has been a topic of considerable debate. In the opinion of most authorities, a normal TSH level essentially rules out hypothyroidism.

Medical texts and review articles are almost unanimous in recommending levothyroxine (T4) as the only appropriate treatment for hypothyroidism. (1,2) These sources acknowledge the human thyroid gland secretes both T4 and T3, in a ratio of approximately 9 to 1. Their reason for recommending only T4 is that peripheral (i.e., extrathyroidal) tissues are capable of converting T4, which is really a prohormone, into its biologically active form, T3. Thus, administration of T4 provides a constant reservoir from which the body can meet its needs for T3. Most authorities discourage the use of T3-containing preparations for thyroid-replacement therapy. They point out that T3 is rapidly absorbed and has a relatively short half-life, resulting in wide between-dose fluctuations in serum T3 levels that are not physiologic. Thus, it is argued, a person taking a T3-containmg preparation might have a supraphysiological serum T3 concentration for several hours after each close, followed by tin excessive decline in T3 level. The fact that commercially available preparations (such as desiccated thyroid and synthetic T4/T3 combinations) contain 20-percent T3 (compared with 10 percent in human thyroid secretions) further exacerbates the problem, according to the prevailing point of view.

Another View of Hypothyroidism

The conventional approach to diagnosing and treating hypothyroidism has been of benefit to millions of patients. However, in the experience of this author and a number of other practitioners (perhaps between several hundred and a few thousand in the United States), reliance solely on this approach causes an unusually large number of patients to be misdiagnosed and deprived of effective treatment.

With regard to diagnosis, it appears many people have clinical hypothyroidism that is not detectable by standard laboratory tests. This syndrome of hypothyroidism with normal blood tests might reasonably be called "sub-laboratory hypothyroidism." In addition to the apparent lack of sensitivity of current diagnostic methods, the conventional treatment for hypothyroidism (both the laboratory-documented and sub-laboratory types) can yield less-than-ideal results. This author has observed a significant number of hypothyroid patients treated with appropriate doses of levothyroxine fail to experience adequate symptom relief, and some patients do not improve at all. Many, although not all, of these levothyroxine nonresponders fare significantly better with Armour[R] thyroid (a brand of desiccated thyroid derived from porcine thyroid gland).