Posted by Thomas Repas, DO, FACP, FACE, CDE January 6, 2009 09:49 AM
Most board-certified endocrinologists avoid desiccated thyroid in the management of hypothyroidism for additional reasons.
Desiccated thyroid preparations contain an approximately 4:1 ratio of thyroxine (T4) to triiodothyronine (T3), whereas the normal human thyroid has of a ratio of 11:1. These preparations result in supraphysiologic levels of T3 in the two to four hours after ingestion. This is due to the rapid release of T3 from thyroglobulin and the immediate almost complete absorption of T3.
In my own practice, I have seen numerous individuals referred to me on desiccated thyroid with fully suppressed thyroid-stimulating hormone. This is because the dose was titrated based on symptoms or clinical findings rather than biochemical assays. Some have had anxiety, insomnia, tremulousness, heat intolerance and other symptoms clearly due to iatrogenic hyperthyroidism. The long-term consequences of hyperthyroidism are not benign. Nevertheless, many have absolutely refused to allow me to decrease their dose, despite my concerns.
With hormone therapy, just as too little is unacceptable, too much is also unacceptable. More is not always better.
Some alternative care practitioners claim that standardized laboratory testing is unreliable. They use other methods to justify their approach such as basal body temperature measurement, testing of tendon reflexes and how the patient generally feels subjectively.
Although thyroid hormone certainly has effects on metabolism, in order for there to be a consistently measurable increase in body temperature, many patients must be rendered hyperthyroid. There are many other factors that affect basal body temperature, not only the thyroid. In addition, there is wide intra-individual variation in body temperature. Body temperature varies depending on time of day and how it is measured. “Normal” body temperature should not be defined as 98.6º F ± 0º, just as we do not define “normal” TSH as exactly 1.00 mIU/L. Normal is a range, not a single value. Using basal body temperature to modify the dose of thyroid HT is imprecise and not supported by the scientific evidence. It is the same with measurement of reflexes and other non-specific clinical findings.
Regarding symptoms and the subjective feeling of wellness, that is problematic. My goal is not only to prevent and treat disease, but for all of my patients to feel better on whatever therapy we have chosen. The problem here is that there are innumerable reasons to feel poorly, often with identical symptoms to hypothyroidism, and yet not due to thyroid dysfunction.
Too many times have I seen other medical diagnoses missed, because every symptom a patient had was attributed to their thyroid and no further evaluation was done. It is easier and less time consuming to write a prescription than it is to think, ask questions and most important of all … to listen.
Sometimes we need to tell patients what they need to hear, even if it is not what they would like to hear. This should be done as kindly and tactfully as possible, but it must be done nonetheless.